Extensions to the C Language Family
***********************************

GNU C provides several language features not found in ISO standard C. (The -pedantic option directs GCC to print a warning message if any of these features is used.)  To test for the availability of these features in conditional compilation, check for a predefined macro __GNUC__, which is always defined under GCC.

These extensions are available in C and Objective-C.  Most of them are also available in C++.  See Extensions to the C++ Language, for extensions that apply only to C++.

Some features that are in ISO C99 but not C89 or C++ are also, as extensions, accepted by GCC in C89 mode and in C++.

Statements and Declarations in Expressions
==========================================

A compound statement enclosed in parentheses may appear as an expression in GNU C.  This allows you to use loops, switches, and local variables within an expression.

Recall that a compound statement is a sequence of statements surrounded by braces; in this construct, parentheses go around the braces.  For example:

     ({ int y = foo (); int z;
        if (y > 0) z = y;
        else z = - y;
        z; })

is a valid (though slightly more complex than necessary) expression for the absolute value of foo ().

The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct.  (If you use some other kind of statement last within the braces, the construct has type void, and thus effectively no value.)

This feature is especially useful in making macro definitions ``safe'' (so that they evaluate each operand exactly once).  For example, the ``maximum'' function is commonly defined as a macro in standard C as follows:

     #define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either A or B twice, with bad results if the operand has side effects.  In GNU C, if you know the type of the operands (here taken as int), you can define the macro safely as follows:

     #define maxint(a,b) \
       ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

Embedded statements are not allowed in constant expressions, such as the value of an enumeration constant, the width of a bit-field, or the initial value of a static variable.

If you don't know the type of the operand, you can still do this, but you must use typeof (see Typeof).

In G++, the result value of a statement expression undergoes array and function pointer decay, and is returned by value to the enclosing expression.  For instance, if A is a class, then

             A a;

             ({a;}).Foo ()

will construct a temporary A object to hold the result of the statement expression, and that will be used to invoke Foo. Therefore the this pointer observed by Foo will not be the address of a.

Any temporaries created within a statement within a statement expression will be destroyed at the statement's end.  This makes statement expressions inside macros slightly different from function calls.  In the latter case temporaries introduced during argument evaluation will be destroyed at the end of the statement that includes the function call.  In the statement expression case they will be destroyed during the statement expression.  For instance,

     #define macro(a)  ({__typeof__(a) b = (a); b + 3; })
     template<typename T> T function(T a) { T b = a; return b + 3; }

     void foo ()
     {
       macro (X ());
       function (X ());
     }

will have different places where temporaries are destroyed.  For the macro case, the temporary X will be destroyed just after the initialization of b.  In the function case that temporary will be destroyed when the function returns.

These considerations mean that it is probably a bad idea to use statement-expressions of this form in header files that are designed to work with C++.  (Note that some versions of the GNU C Library contained header files using statement-expression that lead to precisely this bug.)

Jumping into a statement expression with goto or using a switch statement outside the statement expression with a case or default label inside the statement expression is not permitted.  Jumping into a statement expression with a computed goto (see Labels as Values) yields undefined behavior. Jumping out of a statement expression is permitted, but if the statement expression is part of a larger expression then it is unspecified which other subexpressions of that expression have been evaluated except where the language definition requires certain subexpressions to be evaluated before or after the statement expression.  In any case, as with a function call the evaluation of a statement expression is not interleaved with the evaluation of other parts of the containing expression.  For example,

       foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();

will call foo and bar1 and will not call baz but may or may not call bar2.  If bar2 is called, it will be called after foo and before bar1

Locally Declared Labels
=======================

GCC allows you to declare local labels in any nested block scope.  A local label is just like an ordinary label, but you can only reference it (with a goto statement, or by taking its address) within the block in which it was declared.

A local label declaration looks like this:

     __label__ LABEL;

or

     __label__ LABEL1, LABEL2, /* ... */;

Local label declarations must come at the beginning of the block, before any ordinary declarations or statements.

The label declaration defines the label name, but does not define the label itself.  You must do this in the usual way, with LABEL:, within the statements of the statement expression.

The local label feature is useful for complex macros.  If a macro contains nested loops, a goto can be useful for breaking out of them.  However, an ordinary label whose scope is the whole function cannot be used: if the macro can be expanded several times in one function, the label will be multiply defined in that function.  A local label avoids this problem.  For example:

     #define SEARCH(value, array, target)              \
     do {                                              \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { (value) = i; goto found; }              \
       (value) = -1;                                   \
      found:;                                          \
     } while (0)

This could also be written using a statement-expression:

     #define SEARCH(array, target)                     \
     ({                                                \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { value = i; goto found; }                \
       value = -1;                                     \
      found:                                           \
       value;                                          \
     })

Local label declarations also make the labels they declare visible to nested functions, if there are any.  See Nested Functions, for details.

Labels as Values
================

You can get the address of a label defined in the current function (or a containing function) with the unary operator &&.  The value has type void *.  This value is a constant and can be used wherever a constant of that type is valid.  For example:

     void *ptr;
     /* ... */
     ptr = &&foo;

To use these values, you need to be able to jump to one.  This is done with the computed goto statement (The analogous feature in Fortran is called an assigned goto, but that name seems inappropriate in C, where one can do more than simply store label addresses in label variables.), goto *EXP;.  For example,

     goto *ptr;

Any expression of type void * is allowed.

One way of using these constants is in initializing a static array that will serve as a jump table:

     static void *array[] = { &&foo, &&bar, &&hack };

Then you can select a label with indexing, like this:

     goto *array[i];

Note that this does not check whether the subscript is in bounds---array indexing in C never does that.

Such an array of label values serves a purpose much like that of the switch statement.  The switch statement is cleaner, so use that rather than an array unless the problem does not fit a switch statement very well.

Another use of label values is in an interpreter for threaded code. The labels within the interpreter function can be stored in the threaded code for super-fast dispatching.

You may not use this mechanism to jump to code in a different function. If you do that, totally unpredictable things will happen.  The best way to avoid this is to store the label address only in automatic variables and never pass it as an argument.

An alternate way to write the above example is

     static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                                  &&hack - &&foo };
     goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces the number of dynamic relocations that are needed, and by consequence, allows the data to be read-only.

Nested Functions
================

A nested function is a function defined inside another function. (Nested functions are not supported for GNU C++.)  The nested function's name is local to the block where it is defined.  For example, here we define a nested function named square, and call it twice:

     foo (double a, double b)
     {
       double square (double z) { return z * z; }

       return square (a) + square (b);
     }

The nested function can access all the variables of the containing function that are visible at the point of its definition.  This is called lexical scoping.  For example, here we show a nested function which uses an inherited variable named offset:

     bar (int *array, int offset, int size)
     {
       int access (int *array, int index)
         { return array[index + offset]; }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
     }

Nested function definitions are permitted within functions in the places where variable definitions are allowed; that is, in any block, mixed with the other declarations and statements in the block.

It is possible to call the nested function from outside the scope of its name by storing its address or passing the address to another function:

     hack (int *array, int size)
     {
       void store (int index, int value)
         { array[index] = value; }

       intermediate (store, size);
     }

Here, the function intermediate receives the address of store as an argument.  If intermediate calls store, the arguments given to store are used to store into array. But this technique works only so long as the containing function (hack, in this example) does not exit.

If you try to call the nested function through its address after the containing function has exited, all hell will break loose.  If you try to call it after a containing scope level has exited, and if it refers to some of the variables that are no longer in scope, you may be lucky, but it's not wise to take the risk.  If, however, the nested function does not refer to anything that has gone out of scope, you should be safe.

GCC implements taking the address of a nested function using a technique called trampolines.  A paper describing them is available as

http://people.debian.org/~aaronl/Usenix88-lexic.pdf.

A nested function can jump to a label inherited from a containing function, provided the label was explicitly declared in the containing function (see Local Labels).  Such a jump returns instantly to the containing function, exiting the nested function which did the goto and any intermediate functions as well.  Here is an example:

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
       /* ... */
       return 0;

      /* Control comes here from access
         if it detects an error.  */
      failure:
       return -1;
     }

A nested function always has no linkage.  Declaring one with extern or static is erroneous.  If you need to declare the nested function before its definition, use auto (which is otherwise meaningless for function declarations).

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       auto int access (int *, int);
       /* ... */
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       /* ... */
     }

Constructing Function Calls
===========================

Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.

You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).

However, these built-in functions may interact badly with some sophisticated features or other extensions of the language.  It is, therefore, not recommended to use them outside very simple functions acting as mere forwarders for their arguments.

 -- Built-in Function: void * __builtin_apply_args ()
     This built-in function returns a pointer to data describing how to perform a call with the same arguments as were passed to the current function.

     The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack.  Then it returns the address of that block.

 -- Built-in Function: void * __builtin_apply (void (*FUNCTION)(), void *ARGUMENTS, size_t SIZE)
     This built-in function invokes FUNCTION with a copy of the parameters described by ARGUMENTS and SIZE.

     The value of ARGUMENTS should be the value returned by __builtin_apply_args.  The argument SIZE specifies the size of the stack argument data, in bytes.

     This function returns a pointer to data describing how to return whatever value was returned by FUNCTION.  The data is saved in a block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The value is used by __builtin_apply to compute the amount of data that should be pushed on the stack and copied from the incoming argument area.

 -- Built-in Function: void __builtin_return (void *RESULT)
     This built-in function returns the value described by RESULT from the containing function.  You should specify, for RESULT, a value returned by __builtin_apply.

Referring to a Type with typeof
===============================

Another way to refer to the type of an expression is with typeof. The syntax of using of this keyword looks like sizeof, but the construct acts semantically like a type name defined with typedef.

There are two ways of writing the argument to typeof: with an expression or with a type.  Here is an example with an expression:

     typeof (x[0](1))

This assumes that x is an array of pointers to functions; the type described is that of the values of the functions.

Here is an example with a typename as the argument:

     typeof (int *)

Here the type described is that of pointers to int.

If you are writing a header file that must work when included in ISO C programs, write __typeof__ instead of typeof. See Alternate Keywords.

A typeof-construct can be used anywhere a typedef name could be used.  For example, you can use it in a declaration, in a cast, or inside of sizeof or typeof.

typeof is often useful in conjunction with the statements-within-expressions feature.  Here is how the two together can be used to define a safe ``maximum'' macro that operates on any arithmetic type and evaluates each of its arguments exactly once:

     #define max(a,b) \
       ({ typeof (a) _a = (a); \
           typeof (b) _b = (b); \
         _a > _b ? _a : _b; })

The reason for using names that start with underscores for the local variables is to avoid conflicts with variable names that occur within the expressions that are substituted for a and b.  Eventually we hope to design a new form of declaration syntax that allows you to declare variables whose scopes start only after their initializers; this will be a more reliable way to prevent such conflicts.

Some more examples of the use of typeof:

  * This declares y with the type of what x points to.

          typeof (*x) y;

  * This declares y as an array of such values.

          typeof (*x) y[4];

  * This declares y as an array of pointers to characters:

          typeof (typeof (char *)[4]) y;

     It is equivalent to the following traditional C declaration:

          char *y[4];

     To see the meaning of the declaration using typeof, and why it might be a useful way to write, rewrite it with these macros:

          #define pointer(T)  typeof(T *)
          #define array(T, N) typeof(T [N])

     Now the declaration can be rewritten this way:

          array (pointer (char), 4) y;

     Thus, array (pointer (char), 4) is the type of arrays of 4 pointers to char.

Compatibility Note: In addition to typeof, GCC 2 supported a more limited extension which permitted one to write

     typedef T = EXPR;

with the effect of declaring T to have the type of the expression EXPR.  This extension does not work with GCC 3 (versions between 3.0 and 3.2 will crash; 3.2.1 and later give an error).  Code which relies on it should be rewritten to use typeof:

     typedef typeof(EXPR) T;

This will work with all versions of GCC.

Conditionals with Omitted Operands
==================================

The middle operand in a conditional expression may be omitted.  Then if the first operand is nonzero, its value is the value of the conditional expression.

Therefore, the expression

     x ? : y

has the value of x if that is nonzero; otherwise, the value of y.

This example is perfectly equivalent to

     x ? x : y

In this simple case, the ability to omit the middle operand is not especially useful.  When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect.  Then repeating the operand in the middle would perform the side effect twice.  Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.

Double-Word Integers
====================

ISO C99 supports data types for integers that are at least 64 bits wide, and as an extension GCC supports them in C89 mode and in C++. Simply write long long int for a signed integer, or unsigned long long int for an unsigned integer.  To make an integer constant of type long long int, add the suffix LL to the integer.  To make an integer constant of type unsigned long long int, add the suffix ULL to the integer.

You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines.  Multiplication is open-coded if the machine supports fullword-to-doubleword a widening multiply instruction.  Division and shifts are open-coded only on machines that provide special support.  The operations that are not open-coded use special library routines that come with GCC.

There may be pitfalls when you use long long types for function arguments, unless you declare function prototypes.  If a function expects type int for its argument, and you pass a value of type long long int, confusion will result because the caller and the subroutine will disagree about the number of bytes for the argument. Likewise, if the function expects long long int and you pass int.  The best way to avoid such problems is to use prototypes.

Complex Numbers
===============

ISO C99 supports complex floating data types, and as an extension GCC supports them in C89 mode and in C++, and supports complex integer data types which are not part of ISO C99.  You can declare complex types using the keyword _Complex.  As an extension, the older GNU keyword __complex__ is also supported.

For example, _Complex double x; declares x as a variable whose real part and imaginary part are both of type double.  _Complex short int y; declares y to have real and imaginary parts of type short int; this is not likely to be useful, but it shows that the set of complex types is complete.

To write a constant with a complex data type, use the suffix i or j (either one; they are equivalent).  For example, 2.5fi has type _Complex float and 3i has type _Complex int.  Such a constant always has a pure imaginary value, but you can form any complex value you like by adding one to a real constant.  This is a GNU extension; if you have an ISO C99 conforming C library (such as GNU libc), and want to construct complex constants of floating type, you should include <complex.h> and use the macros I or _Complex_I instead.

To extract the real part of a complex-valued expression EXP, write __real__ EXP.  Likewise, use __imag__ to extract the imaginary part.  This is a GNU extension; for values of floating type, you should use the ISO C99 functions crealf, creal, creall, cimagf, cimag and cimagl, declared in <complex.h> and also provided as built-in functions by GCC.

The operator ~ performs complex conjugation when used on a value with a complex type.  This is a GNU extension; for values of floating type, you should use the ISO C99 functions conjf, conj and conjl, declared in <complex.h> and also provided as built-in functions by GCC.

GCC can allocate complex automatic variables in a noncontiguous fashion; it's even possible for the real part to be in a register while the imaginary part is on the stack (or vice-versa).  Only the DWARF2 debug info format can represent this, so use of DWARF2 is recommended. If you are using the stabs debug info format, GCC describes a noncontiguous complex variable as if it were two separate variables of noncomplex type. If the variable's actual name is foo, the two fictitious variables are named foo$real and foo$imag.  You can examine and set these two fictitious variables with your debugger.

Decimal Floating Types
======================

As an extension, the GNU C compiler supports decimal floating types as defined in the N1176 draft of ISO/IEC WDTR24732.  Support for decimal floating types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change.  Not all targets support decimal floating types.

The decimal floating types are _Decimal32, _Decimal64, and _Decimal128.  They use a radix of ten, unlike the floating types float, double, and long double whose radix is not specified by the C standard but is usually two.

Support for decimal floating types includes the arithmetic operators add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types.  Use a suffix df or DF in a literal constant of type _Decimal32, dd or DD for _Decimal64, and dl or DL for _Decimal128.

GCC support of decimal float as specified by the draft technical report is incomplete:

  * Translation time data type (TTDT) is not supported.

  * Characteristics of decimal floating types are defined in header file decfloat.h rather than float.h.

  * When the value of a decimal floating type cannot be represented in the integer type to which it is being converted, the result is undefined rather than the result value specified by the draft technical report.

Types _Decimal32, _Decimal64, and _Decimal128 are supported by the DWARF2 debug information format.

Hex Floats
==========

ISO C99 supports floating-point numbers written not only in the usual decimal notation, such as 1.55e1, but also numbers such as 0x1.fp3 written in hexadecimal format.  As a GNU extension, GCC supports this in C89 mode (except in some cases when strictly conforming) and in C++.  In that format the 0x hex introducer and the p or P exponent field are mandatory.  The exponent is a decimal number that indicates the power of 2 by which the significant part will be multiplied.  Thus 0x1.f is 1 15/16, p3 multiplies it by 8, and the value of 0x1.fp3 is the same as 1.55e1.

Unlike for floating-point numbers in the decimal notation the exponent is always required in the hexadecimal notation.  Otherwise the compiler would not be able to resolve the ambiguity of, e.g., 0x1.f.  This could mean 1.0f or 1.9375 since f is also the extension for floating-point constants of type float.

Arrays of Length Zero
=====================

Zero-length arrays are allowed in GNU C.  They are very useful as the last element of a structure which is really a header for a variable-length object:

     struct line {
       int length;
       char contents[0];
     };

     struct line *thisline = (struct line *)
       malloc (sizeof (struct line) + this_length);
     thisline->length = this_length;

In ISO C90, you would have to give contents a length of 1, which means either you waste space or complicate the argument to malloc.

In ISO C99, you would use a flexible array member, which is slightly different in syntax and semantics:

  * Flexible array members are written as contents[] without the 0.

  * Flexible array members have incomplete type, and so the sizeof operator may not be applied.  As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero.

  * Flexible array members may only appear as the last member of a struct that is otherwise non-empty.

  * A structure containing a flexible array member, or a union containing such a structure (possibly recursively), may not be a member of a structure or an element of an array.  (However, these uses are permitted by GCC as extensions.)

GCC versions before 3.0 allowed zero-length arrays to be statically initialized, as if they were flexible arrays.  In addition to those cases that were useful, it also allowed initializations in situations that would corrupt later data.  Non-empty initialization of zero-length arrays is now treated like any case where there are more initializer elements than the array holds, in that a suitable warning about "excess elements in array" is given, and the excess elements (all of them, in this case) are ignored.

Instead GCC allows static initialization of flexible array members. This is equivalent to defining a new structure containing the original structure followed by an array of sufficient size to contain the data. I.e. in the following, f1 is constructed as if it were declared like f2.

     struct f1 {
       int x; int y[];
     } f1 = { 1, { 2, 3, 4 } };

     struct f2 {
       struct f1 f1; int data[3];
     } f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that f1 has the desired type, eliminating the need to consistently refer to f2.f1.

This has symmetry with normal static arrays, in that an array of unknown size is also written with [].

Of course, this extension only makes sense if the extra data comes at the end of a top-level object, as otherwise we would be overwriting data at subsequent offsets.  To avoid undue complication and confusion with initialization of deeply nested arrays, we simply disallow any non-empty initialization except when the structure is the top-level object.  For example:

     struct foo { int x; int y[]; };
     struct bar { struct foo z; };

     struct foo a = { 1, { 2, 3, 4 } };        // Valid.
     struct bar b = { { 1, { 2, 3, 4 } } };    // Invalid.
     struct bar c = { { 1, { } } };            // Valid.
     struct foo d[1] = { { 1 { 2, 3, 4 } } };  // Invalid.

Structures With No Members
==========================

GCC permits a C structure to have no members:

     struct empty {
     };

The structure will have size zero.  In C++, empty structures are part of the language.  G++ treats empty structures as if they had a single member of type char.

Arrays of Variable Length
=========================

Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C89 mode and in C++.  (However, GCC's implementation of variable-length arrays does not yet conform in detail to the ISO C99 standard.)  These arrays are declared like any other automatic arrays, but with a length that is not a constant expression.  The storage is allocated at the point of declaration and deallocated when the brace-level is exited.  For example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

Jumping or breaking out of the scope of the array name deallocates the storage.  Jumping into the scope is not allowed; you get an error message for it.

You can use the function alloca to get an effect much like variable-length arrays.  The function alloca is available in many other C implementations (but not in all).  On the other hand, variable-length arrays are more elegant.

There are other differences between these two methods.  Space allocated with alloca exists until the containing function returns. The space for a variable-length array is deallocated as soon as the array name's scope ends.  (If you use both variable-length arrays and alloca in the same function, deallocation of a variable-length array will also deallocate anything more recently allocated with alloca.)

You can also use variable-length arrays as arguments to functions:

     struct entry
     tester (int len, char data[len][len])
     {
       /* ... */
     }

The length of an array is computed once when the storage is allocated and is remembered for the scope of the array in case you access it with sizeof.

If you want to pass the array first and the length afterward, you can use a forward declaration in the parameter list---another GNU extension.

     struct entry
     tester (int len; char data[len][len], int len)
     {
       /* ... */
     }

The int len before the semicolon is a parameter forward declaration, and it serves the purpose of making the name len known when the declaration of data is parsed.

You can write any number of such parameter forward declarations in the parameter list.  They can be separated by commas or semicolons, but the last one must end with a semicolon, which is followed by the ``real'' parameter declarations.  Each forward declaration must match a ``real'' declaration in parameter name and data type.  ISO C99 does not support parameter forward declarations.

Macros with a Variable Number of Arguments.
===========================================

In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can.  The syntax for defining the macro is similar to that of a function.  Here is an example:

     #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

Here ... is a variable argument.  In the invocation of such a macro, it represents the zero or more tokens until the closing parenthesis that ends the invocation, including any commas.  This set of tokens replaces the identifier __VA_ARGS__ in the macro body wherever it appears.  See the CPP manual for more information.

GCC has long supported variadic macros, and used a different syntax that allowed you to give a name to the variable arguments just like any other argument.  Here is an example:

     #define debug(format, args...) fprintf (stderr, format, args)

This is in all ways equivalent to the ISO C example above, but arguably more readable and descriptive.

GNU CPP has two further variadic macro extensions, and permits them to be used with either of the above forms of macro definition.

In standard C, you are not allowed to leave the variable argument out entirely; but you are allowed to pass an empty argument.  For example, this invocation is invalid in ISO C, because there is no comma after the string:

     debug ("A message")

GNU CPP permits you to completely omit the variable arguments in this way.  In the above examples, the compiler would complain, though since the expansion of the macro still has the extra comma after the format string.

To help solve this problem, CPP behaves specially for variable arguments used with the token paste operator, ##.  If instead you write

     #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

and if the variable arguments are omitted or empty, the ## operator causes the preprocessor to remove the comma before it.  If you do provide some variable arguments in your macro invocation, GNU CPP does not complain about the paste operation and instead places the variable arguments after the comma.  Just like any other pasted macro argument, these arguments are not macro expanded.

Slightly Looser Rules for Escaped Newlines
==========================================

Recently, the preprocessor has relaxed its treatment of escaped newlines.  Previously, the newline had to immediately follow a backslash.  The current implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and form feeds between the backslash and the subsequent newline.  The preprocessor issues a warning, but treats it as a valid escaped newline and combines the two lines to form a single logical line.  This works within comments and tokens, as well as between tokens.  Comments are not treated as whitespace for the purposes of this relaxation, since they have not yet been replaced with spaces.

Non-Lvalue Arrays May Have Subscripts
=====================================

In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted, although they may not be modified or used after the next sequence point and the unary & operator may not be applied to them.  As an extension, GCC allows such arrays to be subscripted in C89 mode, though otherwise they do not decay to pointers outside C99 mode.  For example, this is valid in GNU C though not valid in C89:

     struct foo {int a[4];};

     struct foo f();

     bar (int index)
     {
       return f().a[index];
     }

Arithmetic on void- and Function-Pointers
=========================================

In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions.  This is done by treating the size of a void or of a function as 1.

A consequence of this is that sizeof is also allowed on void and on function types, and returns 1.

The option -Wpointer-arith requests a warning if these extensions are used.

Non-Constant Initializers
=========================

As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic variable are not required to be constant expressions in GNU C. Here is an example of an initializer with run-time varying elements:

     foo (float f, float g)
     {
       float beat_freqs[2] = { f-g, f+g };
       /* ... */
     }

Compound Literals
=================

ISO C99 supports compound literals.  A compound literal looks like a cast containing an initializer.  Its value is an object of the type specified in the cast, containing the elements specified in the initializer; it is an lvalue.  As an extension, GCC supports compound literals in C89 mode and in C++.

Usually, the specified type is a structure.  Assume that struct foo and structure are declared as shown:

     struct foo {int a; char b[2];} structure;

Here is an example of constructing a struct foo with a compound literal:

     structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

     {
       struct foo temp = {x + y, 'a', 0};
       structure = temp;
     }

You can also construct an array.  If all the elements of the compound literal are (made up of) simple constant expressions, suitable for use in initializers of objects of static storage duration, then the compound literal can be coerced to a pointer to its first element and used in such an initializer, as shown here:

     char **foo = (char *[]) { "x", "y", "z" };

Compound literals for scalar types and union types are is also allowed, but then the compound literal is equivalent to a cast.

As a GNU extension, GCC allows initialization of objects with static storage duration by compound literals (which is not possible in ISO C99, because the initializer is not a constant). It is handled as if the object was initialized only with the bracket enclosed list if the types of the compound literal and the object match. The initializer list of the compound literal must be constant. If the object being initialized has array type of unknown size, the size is determined by compound literal size.

     static struct foo x = (struct foo) {1, 'a', 'b'};
     static int y[] = (int []) {1, 2, 3};
     static int z[] = (int [3]) {1};

The above lines are equivalent to the following:

     static struct foo x = {1, 'a', 'b'};
     static int y[] = {1, 2, 3};
     static int z[] = {1, 0, 0};

Designated Initializers
=======================

Standard C89 requires the elements of an initializer to appear in a fixed order, the same as the order of the elements in the array or structure being initialized.

In ISO C99 you can give the elements in any order, specifying the array indices or structure field names they apply to, and GNU C allows this as an extension in C89 mode as well.  This extension is not implemented in GNU C++.

To specify an array index, write [INDEX] = before the element value.  For example,

     int a[6] = { [4] = 29, [2] = 15 };

is equivalent to

     int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being initialized is automatic.

An alternative syntax for this which has been obsolete since GCC 2.5 but GCC still accepts is to write [INDEX] before the element value, with no =.

To initialize a range of elements to the same value, write [FIRST ... LAST] = VALUE.  This is a GNU extension.  For example,

     int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side-effects, the side-effects will happen only once, not for each initialized field by the range initializer.

Note that the length of the array is the highest value specified plus one.

In a structure initializer, specify the name of a field to initialize with .FIELDNAME = before the element value.  For example, given the following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

Another syntax which has the same meaning, obsolete since GCC 2.5, is FIELDNAME:, as shown here:

     struct point p = { y: yvalue, x: xvalue };

The [INDEX] or .FIELDNAME is known as a designator.  You can also use a designator (or the obsolete colon syntax) when initializing a union, to specify which element of the union should be used.  For example,

     union foo { int i; double d; };

     union foo f = { .d = 4 };

will convert 4 to a double to store it in the union using the second element.  By contrast, casting 4 to type union foo would store it into the union as the integer i, since it is an integer.  (see Cast to Union.)

You can combine this technique of naming elements with ordinary C initialization of successive elements.  Each initializer element that does not have a designator applies to the next consecutive element of the array or structure.  For example,

     int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to

     int a[6] = { 0, v1, v2, 0, v4, 0 };

Labeling the elements of an array initializer is especially useful when the indices are characters or belong to an enum type. For example:

     int whitespace[256]
       = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };

You can also write a series of .FIELDNAME and [INDEX] designators before an = to specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair.  For example, with the struct point declaration above:

     struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

If the same field is initialized multiple times, it will have value from the last initialization.  If any such overridden initialization has side-effect, it is unspecified whether the side-effect happens or not. Currently, GCC will discard them and issue a warning.

Case Ranges
===========

You can specify a range of consecutive values in a single case label, like this:

     case LOW ... HIGH:

This has the same effect as the proper number of individual case labels, one for each integer value from LOW to HIGH, inclusive.

This feature is especially useful for ranges of ASCII character codes:

     case 'A' ... 'Z':

Be careful: Write spaces around the ..., for otherwise it may be parsed wrong when you use it with integer values.  For example, write this:

     case 1 ... 5:

rather than this:

     case 1...5:

Cast to a Union Type
====================

A cast to union type is similar to other casts, except that the type specified is a union type.  You can specify the type either with union TAG or with a typedef name.  A cast to union is actually a constructor though, not a cast, and hence does not yield an lvalue like normal casts.  (see Compound Literals.)

The types that may be cast to the union type are those of the members of the union.  Thus, given the following union and variables:

     union foo { int i; double d; };
     int x;
     double y;

both x and y can be cast to type union foo.

Using the cast as the right-hand side of an assignment to a variable of union type is equivalent to storing in a member of the union:

     union foo u;
     /* ... */
     u = (union foo) x  ==  u.i = x
     u = (union foo) y  ==  u.d = y

You can also use the union cast as a function argument:

     void hack (union foo);
     /* ... */
     hack ((union foo) x);

Mixed Declarations and Code
===========================

ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound statements.  As an extension, GCC also allows this in C89 mode.  For example, you could do:

     int i;
     /* ... */
     i++;
     int j = i + 2;

Each identifier is visible from where it is declared until the end of the enclosing block.

Declaring Attributes of Functions
=================================

In GNU C, you declare certain things about functions called in your program which help the compiler optimize function calls and check your code more carefully.

The keyword __attribute__ allows you to specify special attributes when making a declaration.  This keyword is followed by an attribute specification inside double parentheses.  The following attributes are currently defined for functions on all targets: noreturn, returns_twice, noinline, always_inline, flatten, pure, const, nothrow, sentinel, format, format_arg, no_instrument_function, section, constructor, destructor, used, unused, deprecated, weak, malloc, alias, warn_unused_result, nonnull, gnu_inline and externally_visible.  Several other attributes are defined for functions on particular target systems.  Other attributes, including section are supported for variables declarations (see Variable Attributes) and for types (see Type Attributes).

You may also specify attributes with __ preceding and following each keyword.  This allows you to use them in header files without being concerned about a possible macro of the same name.  For example, you may use __noreturn__ instead of noreturn.

See Attribute Syntax, for details of the exact syntax for using attributes.

alias ("TARGET")
     The alias attribute causes the declaration to be emitted as an alias for another symbol, which must be specified.  For instance,

          void __f () { /* Do something. */; }
          void f () __attribute__ ((weak, alias ("__f")));

     defines f to be a weak alias for __f.  In C++, the mangled name for the target must be used.  It is an error if __f is not defined in the same translation unit.

     Not all target machines support this attribute.

always_inline
     Generally, functions are not inlined unless optimization is specified. For functions declared inline, this attribute inlines the function even if no optimization level was specified.

gnu_inline
     This attribute should be used with a function which is also declared with the inline keyword.  It directs GCC to treat the function as if it were defined in gnu89 mode even when compiling in C99 or gnu99 mode.

     If the function is declared extern, then this definition of the function is used only for inlining.  In no case is the function compiled as a standalone function, not even if you take its address explicitly.  Such an address becomes an external reference, as if you had only declared the function, and had not defined it.  This has almost the effect of a macro.  The way to use this is to put a function definition in a header file with this attribute, and put another copy of the function, without extern, in a library file.  The definition in the header file will cause most calls to the function to be inlined.  If any uses of the function remain, they will refer to the single copy in the library.  Note that the two definitions of the functions need not be precisely the same, although if they do not have the same effect your program may behave oddly.

     If the function is neither extern nor static, then the function is compiled as a standalone function, as well as being inlined where possible.

     This is how GCC traditionally handled functions declared inline.  Since ISO C99 specifies a different semantics for inline, this function attribute is provided as a transition measure and as a useful feature in its own right.  This attribute is available in GCC 4.1.3 and later.  It is available if either of the preprocessor macros __GNUC_GNU_INLINE__ or __GNUC_STDC_INLINE__ are defined.  See An Inline Function is As Fast As a Macro.

     Note that since the first version of GCC to support C99 inline semantics is 4.3, earlier versions of GCC which accept this attribute effectively assume that it is always present, whether or not it is given explicitly. In versions prior to 4.3, the only effect of explicitly including it is to disable warnings about using inline functions in C99 mode.

flatten
     Generally, inlining into a function is limited.  For a function marked with this attribute, every call inside this function will be inlined, if possible. Whether the function itself is considered for inlining depends on its size and the current inlining parameters.  The flatten attribute only works reliably in unit-at-a-time mode.

cdecl
     On the Intel 386, the cdecl attribute causes the compiler to assume that the calling function will pop off the stack space used to pass arguments.  This is useful to override the effects of the -mrtd switch.

const
     Many functions do not examine any values except their arguments, and have no effects except the return value.  Basically this is just slightly more strict class than the pure attribute below, since function is not allowed to read global memory.

     Note that a function that has pointer arguments and examines the data pointed to must not be declared const.  Likewise, a function that calls a non-const function usually must not be const.  It does not make sense for a const function to return void.

     The attribute const is not implemented in GCC versions earlier than 2.5.  An alternative way to declare that a function has no side effects, which works in the current version and in some older versions, is as follows:

          typedef int intfn ();

          extern const intfn square;

     This approach does not work in GNU C++ from 2.6.0 on, since the language specifies that the const must be attached to the return value.

constructor
destructor
     The constructor attribute causes the function to be called automatically before execution enters main ().  Similarly, the destructor attribute causes the function to be called automatically after main () has completed or exit () has been called.  Functions with these attributes are useful for initializing data that will be used implicitly during the execution of the program.

     These attributes are not currently implemented for Objective-C.

deprecated
     The deprecated attribute results in a warning if the function is used anywhere in the source file.  This is useful when identifying functions that are expected to be removed in a future version of a program.  The warning also includes the location of the declaration of the deprecated function, to enable users to easily find further information about why the function is deprecated, or what they should do instead.  Note that the warnings only occurs for uses:

          int old_fn () __attribute__ ((deprecated));
          int old_fn ();
          int (*fn_ptr)() = old_fn;

     results in a warning on line 3 but not line 2.

     The deprecated attribute can also be used for variables and types (see Variable Attributes, see Type Attributes.)

dllexport
     On Microsoft Windows targets and Symbian OS targets the dllexport attribute causes the compiler to provide a global pointer to a pointer in a DLL, so that it can be referenced with the dllimport attribute.  On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.

     You can use __declspec(dllexport) as a synonym for __attribute__ ((dllexport)) for compatibility with other compilers.

     On systems that support the visibility attribute, this attribute also implies ``default'' visibility, unless a visibility attribute is explicitly specified.  You should avoid the use of dllexport with ``hidden'' or ``internal'' visibility; in the future GCC may issue an error for those cases.

     Currently, the dllexport attribute is ignored for inlined functions, unless the -fkeep-inline-functions flag has been used.  The attribute is also ignored for undefined symbols.

     When applied to C++ classes, the attribute marks defined non-inlined member functions and static data members as exports.  Static consts initialized in-class are not marked unless they are also defined out-of-class.

     For Microsoft Windows targets there are alternative methods for including the symbol in the DLL's export table such as using a .def file with an EXPORTS section or, with GNU ld, using the --export-all linker flag.

dllimport
     On Microsoft Windows and Symbian OS targets, the dllimport attribute causes the compiler to reference a function or variable via a global pointer to a pointer that is set up by the DLL exporting the symbol.  The attribute implies extern storage.  On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.

     You can use __declspec(dllimport) as a synonym for __attribute__ ((dllimport)) for compatibility with other compilers.

     Currently, the attribute is ignored for inlined functions.  If the attribute is applied to a symbol definition, an error is reported. If a symbol previously declared dllimport is later defined, the attribute is ignored in subsequent references, and a warning is emitted. The attribute is also overridden by a subsequent declaration as dllexport.

     When applied to C++ classes, the attribute marks non-inlined member functions and static data members as imports.  However, the attribute is ignored for virtual methods to allow creation of vtables using thunks.

     On the SH Symbian OS target the dllimport attribute also has another affect---it can cause the vtable and run-time type information for a class to be exported.  This happens when the class has a dllimport'ed constructor or a non-inline, non-pure virtual function and, for either of those two conditions, the class also has a inline constructor or destructor and has a key function that is defined in the current translation unit.

     For Microsoft Windows based targets the use of the dllimport attribute on functions is not necessary, but provides a small performance benefit by eliminating a thunk in the DLL.  The use of the dllimport attribute on imported variables was required on older versions of the GNU linker, but can now be avoided by passing the --enable-auto-import switch to the GNU linker.  As with functions, using the attribute for a variable eliminates a thunk in the DLL.

     One drawback to using this attribute is that a pointer to a function or variable marked as dllimport cannot be used as a constant address.  On Microsoft Windows targets, the attribute can be disabled for functions by setting the -mnop-fun-dllimport flag.

eightbit_data
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified variable should be placed into the eight bit data section. The compiler will generate more efficient code for certain operations on data in the eight bit data area.  Note the eight bit data area is limited to 256 bytes of data.

     You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.

exception_handler
     Use this attribute on the Blackfin to indicate that the specified function is an exception handler.  The compiler will generate function entry and exit sequences suitable for use in an exception handler when this attribute is present.

far
     On 68HC11 and 68HC12 the far attribute causes the compiler to use a calling convention that takes care of switching memory banks when entering and leaving a function.  This calling convention is also the default when using the -mlong-calls option.

     On 68HC12 the compiler will use the call and rtc instructions to call and return from a function.

     On 68HC11 the compiler will generate a sequence of instructions to invoke a board-specific routine to switch the memory bank and call the real function.  The board-specific routine simulates a call. At the end of a function, it will jump to a board-specific routine instead of using rts.  The board-specific return routine simulates the rtc.

fastcall
     On the Intel 386, the fastcall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX and the second argument (if of integral type) in the register EDX.  Subsequent and other typed arguments are passed on the stack.  The called function will pop the arguments off the stack.  If the number of arguments is variable all arguments are pushed on the stack.

format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)
     The format attribute specifies that a function takes printf, scanf, strftime or strfmon style arguments which should be type-checked against a format string.  For example, the declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to my_printf for consistency with the printf style format string argument my_format.

     The parameter ARCHETYPE determines how the format string is interpreted, and should be printf, scanf, strftime or strfmon.  (You can also use __printf__, __scanf__, __strftime__ or __strfmon__.)  The parameter STRING-INDEX specifies which argument is the format string argument (starting from 1), while FIRST-TO-CHECK is the number of the first argument to check against the format string.  For functions where the arguments are not available to be checked (such as vprintf), specify the third parameter as zero.  In this case the compiler only checks the format string for consistency.  For strftime formats, the third parameter is required to be zero. Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two, not one, when giving values for STRING-INDEX and FIRST-TO-CHECK.

     In the example above, the format string (my_format) is the second argument of the function my_print, and the arguments to check start with the third argument, so the correct parameters for the format attribute are 2 and 3.

     The format attribute allows you to identify your own functions which take format strings as arguments, so that GCC can check the calls to these functions for errors.  The compiler always (unless -ffreestanding or -fno-builtin is used) checks formats for the standard library functions printf, fprintf, sprintf, scanf, fscanf, sscanf, strftime, vprintf, vfprintf and vsprintf whenever such warnings are requested (using -Wformat), so there is no need to modify the header file stdio.h.  In C99 mode, the functions snprintf, vsnprintf, vscanf, vfscanf and vsscanf are also checked.  Except in strictly conforming C standard modes, the X/Open function strfmon is also checked as are printf_unlocked and fprintf_unlocked. See Options Controlling C Dialect.

     The target may provide additional types of format checks. See Format Checks Specific to Particular Target Machines.

format_arg (STRING-INDEX)
     The format_arg attribute specifies that a function takes a format string for a printf, scanf, strftime or strfmon style function and modifies it (for example, to translate it into another language), so the result can be passed to a printf, scanf, strftime or strfmon style function (with the remaining arguments to the format function the same as they would have been for the unmodified string).  For example, the declaration:

          extern char *
          my_dgettext (char *my_domain, const char *my_format)
                __attribute__ ((format_arg (2)));

     causes the compiler to check the arguments in calls to a printf, scanf, strftime or strfmon type function, whose format string argument is a call to the my_dgettext function, for consistency with the format string argument my_format.  If the format_arg attribute had not been specified, all the compiler could tell in such calls to format functions would be that the format string argument is not constant; this would generate a warning when -Wformat-nonliteral is used, but the calls could not be checked without the attribute.

     The parameter STRING-INDEX specifies which argument is the format string argument (starting from one).  Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two.

     The format-arg attribute allows you to identify your own functions which modify format strings, so that GCC can check the calls to printf, scanf, strftime or strfmon type function whose operands are a call to one of your own function. The compiler always treats gettext, dgettext, and dcgettext in this manner except when strict ISO C support is requested by -ansi or an appropriate -std option, or -ffreestanding or -fno-builtin is used.  See Options Controlling C Dialect.

function_vector
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function should be called through the function vector.  Calling a function through the function vector will reduce code size, however; the function vector has a limited size (maximum 128 entries on the H8/300 and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.

     You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.

interrupt
     Use this attribute on the ARM, AVR, C4x, CRX, M32C, M32R/D, MS1, and Xstormy16 ports to indicate that the specified function is an interrupt handler. The compiler will generate function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

     Note, interrupt handlers for the Blackfin, m68k, H8/300, H8/300H, H8S, and SH processors can be specified via the interrupt_handler attribute.

     Note, on the AVR, interrupts will be enabled inside the function.

     Note, for the ARM, you can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:

          void f () __attribute__ ((interrupt ("IRQ")));

     Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF.

interrupt_handler
     Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S, and SH to indicate that the specified function is an interrupt handler.  The compiler will generate function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

kspisusp
     When used together with interrupt_handler, exception_handler or nmi_handler, code will be generated to load the stack pointer from the USP register in the function prologue.

long_call/short_call
     This attribute specifies how a particular function is called on ARM.  Both attributes override the -mlong-calls (see ARM Options) command line switch and #pragma long_calls settings.  The long_call attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence.   The short_call attribute always places the offset to the function from the call site into the BL instruction directly.

longcall/shortcall
     On the Blackfin, RS/6000 and PowerPC, the longcall attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence.  The shortcall attribute indicates that the function is always close enough for the shorter calling sequence to be used.  These attributes override both the -mlongcall switch and, on the RS/6000 and PowerPC, the #pragma longcall setting.

     See RS/6000 and PowerPC Options, for more information on whether long calls are necessary.

long_call
     This attribute specifies how a particular function is called on MIPS. The attribute overrides the -mlong-calls (see MIPS Options) command line switch.  This attribute causes the compiler to always call the function by first loading its address into a register, and then using the contents of that register.

malloc
     The malloc attribute is used to tell the compiler that a function may be treated as if any non-NULL pointer it returns cannot alias any other pointer valid when the function returns. This will often improve optimization. Standard functions with this property include malloc and calloc.  realloc-like functions have this property as long as the old pointer is never referred to (including comparing it to the new pointer) after the function returns a non-NULL value.

model (MODEL-NAME)

     On the M32R/D, use this attribute to set the addressability of an object, and of the code generated for a function.  The identifier MODEL-NAME is one of small, medium, or large, representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction), and are callable with the bl instruction.

     Medium model objects may live anywhere in the 32-bit address space (the compiler will generate seth/add3 instructions to load their addresses), and are callable with the bl instruction.

     Large model objects may live anywhere in the 32-bit address space (the compiler will generate seth/add3 instructions to load their addresses), and may not be reachable with the bl instruction (the compiler will generate the much slower seth/add3/jl instruction sequence).

     On IA-64, use this attribute to set the addressability of an object. At present, the only supported identifier for MODEL-NAME is small, indicating addressability via ``small'' (22-bit) addresses (so that their addresses can be loaded with the addl instruction).  Caveat: such addressing is by definition not position independent and hence this attribute must not be used for objects defined by shared libraries.

naked
     Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate that the specified function does not need prologue/epilogue sequences generated by the compiler.  It is up to the programmer to provide these sequences.

near
     On 68HC11 and 68HC12 the near attribute causes the compiler to use the normal calling convention based on jsr and rts. This attribute can be used to cancel the effect of the -mlong-calls option.

nesting
     Use this attribute together with interrupt_handler, exception_handler or nmi_handler to indicate that the function entry code should enable nested interrupts or exceptions.

nmi_handler
     Use this attribute on the Blackfin to indicate that the specified function is an NMI handler.  The compiler will generate function entry and exit sequences suitable for use in an NMI handler when this attribute is present.

no_instrument_function
     If -finstrument-functions is given, profiling function calls will be generated at entry and exit of most user-compiled functions. Functions with this attribute will not be so instrumented.

noinline
     This function attribute prevents a function from being considered for inlining.

nonnull (ARG-INDEX, ...)
     The nonnull attribute specifies that some function parameters should be non-null pointers.  For instance, the declaration:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
          	__attribute__((nonnull (1, 2)));

     causes the compiler to check that, in calls to my_memcpy, arguments DEST and SRC are non-null.  If the compiler determines that a null pointer is passed in an argument slot marked as non-null, and the -Wnonnull option is enabled, a warning is issued.  The compiler may also choose to make optimizations based on the knowledge that certain function arguments will not be null.

     If no argument index list is given to the nonnull attribute, all pointer arguments are marked as non-null.  To illustrate, the following declaration is equivalent to the previous example:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
          	__attribute__((nonnull));

noreturn
     A few standard library functions, such as abort and exit, cannot return.  GCC knows this automatically.  Some programs define their own functions that never return.  You can declare them noreturn to tell the compiler this fact.  For example,

          void fatal () __attribute__ ((noreturn));

          void
          fatal (/* ... */)
          {
            /* ... */ /* Print error message. */ /* ... */
            exit (1);
          }

     The noreturn keyword tells the compiler to assume that fatal cannot return.  It can then optimize without regard to what would happen if fatal ever did return.  This makes slightly better code.  More importantly, it helps avoid spurious warnings of uninitialized variables.

     The noreturn keyword does not affect the exceptional path when that applies: a noreturn-marked function may still return to the caller by throwing an exception or calling longjmp.

     Do not assume that registers saved by the calling function are restored before calling the noreturn function.

     It does not make sense for a noreturn function to have a return type other than void.

     The attribute noreturn is not implemented in GCC versions earlier than 2.5.  An alternative way to declare that a function does not return, which works in the current version and in some older versions, is as follows:

          typedef void voidfn ();

          volatile voidfn fatal;

     This approach does not work in GNU C++.

nothrow
     The nothrow attribute is used to inform the compiler that a function cannot throw an exception.  For example, most functions in the standard C library can be guaranteed not to throw an exception with the notable exceptions of qsort and bsearch that take function pointer arguments.  The nothrow attribute is not implemented in GCC versions earlier than 3.3.

pure
     Many functions have no effects except the return value and their return value depends only on the parameters and/or global variables. Such a function can be subject to common subexpression elimination and loop optimization just as an arithmetic operator would be.  These functions should be declared with the attribute pure.  For example,

          int square (int) __attribute__ ((pure));

     says that the hypothetical function square is safe to call fewer times than the program says.

     Some of common examples of pure functions are strlen or memcmp. Interesting non-pure functions are functions with infinite loops or those depending on volatile memory or other system resource, that may change between two consecutive calls (such as feof in a multithreading environment).

     The attribute pure is not implemented in GCC versions earlier than 2.96.

regparm (NUMBER)
     On the Intel 386, the regparm attribute causes the compiler to pass arguments number one to NUMBER if they are of integral type in registers EAX, EDX, and ECX instead of on the stack.  Functions that take a variable number of arguments will continue to be passed all of their arguments on the stack.

     Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default).  Lazy binding will send the first call via resolving code in the loader, which might assume EAX, EDX and ECX can be clobbered, as per the standard calling conventions.  Solaris 8 is affected by this. GNU systems with GLIBC 2.1 or higher, and FreeBSD, are believed to be safe since the loaders there save all registers.  (Lazy binding can be disabled with the linker or the loader if desired, to avoid the problem.)

sseregparm
     On the Intel 386 with SSE support, the sseregparm attribute causes the compiler to pass up to 3 floating point arguments in SSE registers instead of on the stack.  Functions that take a variable number of arguments will continue to pass all of their floating point arguments on the stack.

force_align_arg_pointer
     On the Intel x86, the force_align_arg_pointer attribute may be applied to individual function definitions, generating an alternate prologue and epilogue that realigns the runtime stack.  This supports mixing legacy codes that run with a 4-byte aligned stack with modern codes that keep a 16-byte stack for SSE compatibility.  The alternate prologue and epilogue are slower and bigger than the regular ones, and the alternate prologue requires a scratch register; this lowers the number of registers available if used in conjunction with the regparm attribute.  The force_align_arg_pointer attribute is incompatible with nested functions; this is considered a hard error.

returns_twice
     The returns_twice attribute tells the compiler that a function may return more than one time.  The compiler will ensure that all registers are dead before calling such a function and will emit a warning about the variables that may be clobbered after the second return from the function.  Examples of such functions are setjmp and vfork. The longjmp-like counterpart of such function, if any, might need to be marked with the noreturn attribute.

saveall
     Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to indicate that all registers except the stack pointer should be saved in the prologue regardless of whether they are used or not.

section ("SECTION-NAME")
     Normally, the compiler places the code it generates in the text section. Sometimes, however, you need additional sections, or you need certain particular functions to appear in special sections.  The section attribute specifies that a function lives in a particular section. For example, the declaration:

          extern void foobar (void) __attribute__ ((section ("bar")));

     puts the function foobar in the bar section.

     Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

sentinel
     This function attribute ensures that a parameter in a function call is an explicit NULL.  The attribute is only valid on variadic functions.  By default, the sentinel is located at position zero, the last parameter of the function call.  If an optional integer position argument P is supplied to the attribute, the sentinel must be located at position P counting backwards from the end of the argument list.

          __attribute__ ((sentinel))
          is equivalent to
          __attribute__ ((sentinel(0)))

     The attribute is automatically set with a position of 0 for the built-in functions execl and execlp.  The built-in function execle has the attribute set with a position of 1.

     A valid NULL in this context is defined as zero with any pointer type.  If your system defines the NULL macro with an integer type then you need to add an explicit cast.  GCC replaces stddef.h with a copy that redefines NULL appropriately.

     The warnings for missing or incorrect sentinels are enabled with -Wformat.

short_call
     See long_call/short_call.

shortcall
     See longcall/shortcall.

signal
     Use this attribute on the AVR to indicate that the specified function is a signal handler.  The compiler will generate function entry and exit sequences suitable for use in a signal handler when this attribute is present.  Interrupts will be disabled inside the function.

sp_switch
     Use this attribute on the SH to indicate an interrupt_handler function should switch to an alternate stack.  It expects a string argument that names a global variable holding the address of the alternate stack.

          void *alt_stack;
          void f () __attribute__ ((interrupt_handler,
                                    sp_switch ("alt_stack")));

stdcall
     On the Intel 386, the stdcall attribute causes the compiler to assume that the called function will pop off the stack space used to pass arguments, unless it takes a variable number of arguments.

tiny_data
     Use this attribute on the H8/300H and H8S to indicate that the specified variable should be placed into the tiny data section. The compiler will generate more efficient code for loads and stores on data in the tiny data section.  Note the tiny data area is limited to slightly under 32kbytes of data.

trap_exit
     Use this attribute on the SH for an interrupt_handler to return using trapa instead of rte.  This attribute expects an integer argument specifying the trap number to be used.

unused
     This attribute, attached to a function, means that the function is meant to be possibly unused.  GCC will not produce a warning for this function.

used
     This attribute, attached to a function, means that code must be emitted for the function even if it appears that the function is not referenced. This is useful, for example, when the function is referenced only in inline assembly.

visibility ("VISIBILITY_TYPE")
     This attribute affects the linkage of the declaration to which it is attached. There are four supported VISIBILITY_TYPE values: default, hidden, protected or internal visibility.

          void __attribute__ ((visibility ("protected")))
          f () { /* Do something. */; }
          int i __attribute__ ((visibility ("hidden")));

     The possible values of VISIBILITY_TYPE correspond to the visibility settings in the ELF gABI.

     default
          Default visibility is the normal case for the object file format. This value is available for the visibility attribute to override other options that may change the assumed visibility of entities.

          On ELF, default visibility means that the declaration is visible to other modules and, in shared libraries, means that the declared entity may be overridden.

          On Darwin, default visibility means that the declaration is visible to other modules.

          Default visibility corresponds to ``external linkage'' in the language.

     hidden
          Hidden visibility indicates that the entity declared will have a new form of linkage, which we'll call ``hidden linkage''.  Two declarations of an object with hidden linkage refer to the same object if they are in the same shared object.

     internal
          Internal visibility is like hidden visibility, but with additional processor specific semantics.  Unless otherwise specified by the psABI, GCC defines internal visibility to mean that a function is never called from another module.  Compare this with hidden functions which, while they cannot be referenced directly by other modules, can be referenced indirectly via function pointers.  By indicating that a function cannot be called from outside the module, GCC may for instance omit the load of a PIC register since it is known that the calling function loaded the correct value.

     protected
          Protected visibility is like default visibility except that it indicates that references within the defining module will bind to the definition in that module.  That is, the declared entity cannot be overridden by another module.

     All visibilities are supported on many, but not all, ELF targets (supported when the assembler supports the .visibility pseudo-op).  Default visibility is supported everywhere.  Hidden visibility is supported on Darwin targets.

     The visibility attribute should be applied only to declarations which would otherwise have external linkage.  The attribute should be applied consistently, so that the same entity should not be declared with different settings of the attribute.

     In C++, the visibility attribute applies to types as well as functions and objects, because in C++ types have linkage.  A class must not have greater visibility than its non-static data member types and bases, and class members default to the visibility of their class.  Also, a declaration without explicit visibility is limited to the visibility of its type.

     In C++, you can mark member functions and static member variables of a class with the visibility attribute.  This is useful if if you know a particular method or static member variable should only be used from one shared object; then you can mark it hidden while the rest of the class has default visibility.  Care must be taken to avoid breaking the One Definition Rule; for example, it is usually not useful to mark an inline method as hidden without marking the whole class as hidden.

     A C++ namespace declaration can also have the visibility attribute. This attribute applies only to the particular namespace body, not to other definitions of the same namespace; it is equivalent to using #pragma GCC visibility before and after the namespace definition (see Visibility Pragmas).

     In C++, if a template argument has limited visibility, this restriction is implicitly propagated to the template instantiation. Otherwise, template instantiations and specializations default to the visibility of their template.

     If both the template and enclosing class have explicit visibility, the visibility from the template is used.

warn_unused_result
     The warn_unused_result attribute causes a warning to be emitted if a caller of the function with this attribute does not use its return value.  This is useful for functions where not checking the result is either a security problem or always a bug, such as realloc.

          int fn () __attribute__ ((warn_unused_result));
          int foo ()
          {
            if (fn () < 0) return -1;
            fn ();
            return 0;
          }

     results in warning on line 5.

weak
     The weak attribute causes the declaration to be emitted as a weak symbol rather than a global.  This is primarily useful in defining library functions which can be overridden in user code, though it can also be used with non-function declarations.  Weak symbols are supported for ELF targets, and also for a.out targets when using the GNU assembler and linker.

weakref
weakref ("TARGET")
     The weakref attribute marks a declaration as a weak reference. Without arguments, it should be accompanied by an alias attribute naming the target symbol.  Optionally, the TARGET may be given as an argument to weakref itself.  In either case, weakref implicitly marks the declaration as weak.  Without a TARGET, given as an argument to weakref or to alias, weakref is equivalent to weak.

          static int x() __attribute__ ((weakref ("y")));
          /* is equivalent to... */
          static int x() __attribute__ ((weak, weakref, alias ("y")));
          /* and to... */
          static int x() __attribute__ ((weakref));
          static int x() __attribute__ ((alias ("y")));

     A weak reference is an alias that does not by itself require a definition to be given for the target symbol.  If the target symbol is only referenced through weak references, then the becomes a weak undefined symbol.  If it is directly referenced, however, then such strong references prevail, and a definition will be required for the symbol, not necessarily in the same translation unit.

     The effect is equivalent to moving all references to the alias to a separate translation unit, renaming the alias to the aliased symbol, declaring it as weak, compiling the two separate translation units and performing a reloadable link on them.

     At present, a declaration to which weakref is attached can only be static.

externally_visible
     This attribute, attached to a global variable or function nullify effect of -fwhole-program command line option, so the object remain visible outside the current compilation unit

You can specify multiple attributes in a declaration by separating them by commas within the double parentheses or by immediately following an attribute declaration with another attribute declaration.

Some people object to the __attribute__ feature, suggesting that ISO C's #pragma should be used instead.  At the time __attribute__ was designed, there were two reasons for not doing this.

 1. It is impossible to generate #pragma commands from a macro.

 2. There is no telling what the same #pragma might mean in another compiler.

These two reasons applied to almost any application that might have been proposed for #pragma.  It was basically a mistake to use #pragma for anything.

The ISO C99 standard includes _Pragma, which now allows pragmas to be generated from macros.  In addition, a #pragma GCC namespace is now in use for GCC-specific pragmas.  However, it has been found convenient to use __attribute__ to achieve a natural attachment of attributes to their corresponding declarations, whereas #pragma GCC is of use for constructs that do not naturally form part of the grammar.  See Miscellaneous Preprocessing Directives (The GNU C Preprocessor).

Attribute Syntax
================

This section describes the syntax with which __attribute__ may be used, and the constructs to which attribute specifiers bind, for the C language.  Some details may vary for C++ and Objective-C.  Because of infelicities in the grammar for attributes, some forms described here may not be successfully parsed in all cases.

There are some problems with the semantics of attributes in C++.  For example, there are no manglings for attributes, although they may affect code generation, so problems may arise when attributed types are used in conjunction with templates or overloading.  Similarly, typeid does not distinguish between types with different attributes.  Support for attributes in C++ may be restricted in future to attributes on declarations only, but not on nested declarators.

See Function Attributes, for details of the semantics of attributes applying to functions.  See Variable Attributes, for details of the semantics of attributes applying to variables.  See Type Attributes, for details of the semantics of attributes applying to structure, union and enumerated types.

An attribute specifier is of the form __attribute__ ((ATTRIBUTE-LIST)).  An attribute list is a possibly empty comma-separated sequence of attributes, where each attribute is one of the following:

  * Empty.  Empty attributes are ignored.

  * A word (which may be an identifier such as unused, or a reserved word such as const).

  * A word, followed by, in parentheses, parameters for the attribute. These parameters take one of the following forms:

       * An identifier.  For example, mode attributes use this form.

       * An identifier followed by a comma and a non-empty comma-separated list of expressions.  For example, format attributes use this form.

       * A possibly empty comma-separated list of expressions.  For example, format_arg attributes use this form with the list being a single integer constant expression, and alias attributes use this form with the list being a single string constant.

An attribute specifier list is a sequence of one or more attribute specifiers, not separated by any other tokens.

In GNU C, an attribute specifier list may appear after the colon following a label, other than a case or default label.  The only attribute it makes sense to use after a label is unused.  This feature is intended for code generated by programs which contains labels that may be unused but which is compiled with -Wall.  It would not normally be appropriate to use in it human-written code, though it could be useful in cases where the code that jumps to the label is contained within an #ifdef conditional.  GNU C++ does not permit such placement of attribute lists, as it is permissible for a declaration, which could begin with an attribute list, to be labelled in C++.  Declarations cannot be labelled in C90 or C99, so the ambiguity does not arise there.

An attribute specifier list may appear as part of a struct, union or enum specifier.  It may go either immediately after the struct, union or enum keyword, or after the closing brace.  The former syntax is preferred. Where attribute specifiers follow the closing brace, they are considered to relate to the structure, union or enumerated type defined, not to any enclosing declaration the type specifier appears in, and the type defined is not complete until after the attribute specifiers.

Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for example in the case of a parameter declaration), or to a particular declarator within a declaration.  Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not yet correctly implemented.

Any list of specifiers and qualifiers at the start of a declaration may contain attribute specifiers, whether or not such a list may in that context contain storage class specifiers.  (Some attributes, however, are essentially in the nature of storage class specifiers, and only make sense where storage class specifiers may be used; for example, section.)  There is one necessary limitation to this syntax: the first old-style parameter declaration in a function definition cannot begin with an attribute specifier, because such an attribute applies to the function instead by syntax described below (which, however, is not yet implemented in this case).  In some other cases, attribute specifiers are permitted by this grammar but not yet supported by the compiler.  All attribute specifiers in this place relate to the declaration as a whole.  In the obsolescent usage where a type of int is implied by the absence of type specifiers, such a list of specifiers and qualifiers may be an attribute specifier list with no other specifiers or qualifiers.

At present, the first parameter in a function prototype must have some type specifier which is not an attribute specifier; this resolves an ambiguity in the interpretation of void f(int (__attribute__((foo)) x)), but is subject to change.  At present, if the parentheses of a function declarator contain only attributes then those attributes are ignored, rather than yielding an error or warning or implying a single parameter of type int, but this is subject to change.

An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers.  Such attribute specifiers apply only to the identifier before whose declarator they appear.  For example, in

     __attribute__((noreturn)) void d0 (void),
         __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
          d2 (void)

the noreturn attribute applies to all the functions declared; the format attribute only applies to d1.

An attribute specifier list may appear immediately before the comma, = or semicolon terminating the declaration of an identifier other than a function definition.  At present, such attribute specifiers apply to the declared object or function, but in future they may attach to the outermost adjacent declarator.  In simple cases there is no difference, but, for example, in

     void (****f)(void) __attribute__((noreturn));

at present the noreturn attribute applies to f, which causes a warning since f is not a function, but in future it may apply to the function ****f.  The precise semantics of what attributes in such cases will apply to are not yet specified.  Where an assembler name for an object or function is specified (see Asm Labels), at present the attribute must follow the asm specification; in future, attributes before the asm specification may apply to the adjacent declarator, and those after it to the declared object or function.

An attribute specifier list may, in future, be permitted to appear after the declarator in a function definition (before any old-style parameter declarations or the function body).

Attribute specifiers may be mixed with type qualifiers appearing inside the [] of a parameter array declarator, in the C99 construct by which such qualifiers are applied to the pointer to which the array is implicitly converted.  Such attribute specifiers apply to the pointer, not to the array, but at present this is not implemented and they are ignored.

An attribute specifier list may appear at the start of a nested declarator.  At present, there are some limitations in this usage: the attributes correctly apply to the declarator, but for most individual attributes the semantics this implies are not implemented. When attribute specifiers follow the * of a pointer declarator, they may be mixed with any type qualifiers present. The following describes the formal semantics of this syntax.  It will make the most sense if you are familiar with the formal specification of declarators in the ISO C standard.

Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T D1, where T contains declaration specifiers that specify a type TYPE (such as int) and D1 is a declarator that contains an identifier IDENT.  The type specified for IDENT for derived declarators whose type does not include an attribute specifier is as in the ISO C standard.

If D1 has the form ( ATTRIBUTE-SPECIFIER-LIST D ), and the declaration T D specifies the type ``DERIVED-DECLARATOR-TYPE-LIST TYPE'' for IDENT, then T D1 specifies the type ``DERIVED-DECLARATOR-TYPE-LIST ATTRIBUTE-SPECIFIER-LIST TYPE'' for IDENT.

If D1 has the form * TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST D, and the declaration T D specifies the type ``DERIVED-DECLARATOR-TYPE-LIST TYPE'' for IDENT, then T D1 specifies the type ``DERIVED-DECLARATOR-TYPE-LIST TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST TYPE'' for IDENT.

For example,

     void (__attribute__((noreturn)) ****f) (void);

specifies the type ``pointer to pointer to pointer to pointer to non-returning function returning void''.  As another example,

     char *__attribute__((aligned(8))) *f;

specifies the type ``pointer to 8-byte-aligned pointer to char''. Note again that this does not work with most attributes; for example, the usage of aligned and noreturn attributes given above is not yet supported.

For compatibility with existing code written for compiler versions that did not implement attributes on nested declarators, some laxity is allowed in the placing of attributes.  If an attribute that only applies to types is applied to a declaration, it will be treated as applying to the type of that declaration.  If an attribute that only applies to declarations is applied to the type of a declaration, it will be treated as applying to that declaration; and, for compatibility with code placing the attributes immediately before the identifier declared, such an attribute applied to a function return type will be treated as applying to the function type, and such an attribute applied to an array element type will be treated as applying to the array type.  If an attribute that only applies to function types is applied to a pointer-to-function type, it will be treated as applying to the pointer target type; if such an attribute is applied to a function return type that is not a pointer-to-function type, it will be treated as applying to the function type.

Prototypes and Old-Style Function Definitions
=============================================

GNU C extends ISO C to allow a function prototype to override a later old-style non-prototype definition.  Consider the following example:

     /* Use prototypes unless the compiler is old-fashioned.  */
     #ifdef __STDC__
     #define P(x) x
     #else
     #define P(x) ()
     #endif

     /* Prototype function declaration.  */
     int isroot P((uid_t));

     /* Old-style function definition.  */
     int
     isroot (x)   /* ??? lossage here ??? */
          uid_t x;
     {
       return x == 0;
     }

Suppose the type uid_t happens to be short.  ISO C does not allow this example, because subword arguments in old-style non-prototype definitions are promoted.  Therefore in this example the function definition's argument is really an int, which does not match the prototype argument type of short.

This restriction of ISO C makes it hard to write code that is portable to traditional C compilers, because the programmer does not know whether the uid_t type is short, int, or long.  Therefore, in cases like these GNU C allows a prototype to override a later old-style definition.  More precisely, in GNU C, a function prototype argument type overrides the argument type specified by a later old-style definition if the former type is the same as the latter type before promotion.  Thus in GNU C the above example is equivalent to the following:

     int isroot (uid_t);

     int
     isroot (uid_t x)
     {
       return x == 0;
     }

GNU C++ does not support old-style function definitions, so this extension is irrelevant.

C++ Style Comments
==================

In GNU C, you may use C++ style comments, which start with // and continue until the end of the line.  Many other C implementations allow such comments, and they are included in the 1999 C standard.  However, C++ style comments are not recognized if you specify an -std option specifying a version of ISO C before C99, or -ansi (equivalent to -std=c89).

Dollar Signs in Identifier Names
================================

In GNU C, you may normally use dollar signs in identifier names. This is because many traditional C implementations allow such identifiers. However, dollar signs in identifiers are not supported on a few target machines, typically because the target assembler does not allow them.

The Character ESC in Constants
==============================

You can use the sequence \e in a string or character constant to stand for the ASCII character ESC.

Inquiring on Alignment of Types or Variables
============================================

The keyword __alignof__ allows you to inquire about how an object is aligned, or the minimum alignment usually required by a type.  Its syntax is just like sizeof.

For example, if the target machine requires a double value to be aligned on an 8-byte boundary, then __alignof__ (double) is 8. This is true on many RISC machines.  On more traditional machine designs, __alignof__ (double) is 4 or even 2.

Some machines never actually require alignment; they allow reference to any data type even at an odd address.  For these machines, __alignof__ reports the recommended alignment of a type.

If the operand of __alignof__ is an lvalue rather than a type, its value is the required alignment for its type, taking into account any minimum alignment specified with GCC's __attribute__ extension (see Variable Attributes).  For example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of __alignof__ (foo1.y) is 1, even though its actual alignment is probably 2 or 4, the same as __alignof__ (int).

It is an error to ask for the alignment of an incomplete type.

Specifying Attributes of Variables
==================================

The keyword __attribute__ allows you to specify special attributes of variables or structure fields.  This keyword is followed by an attribute specification inside double parentheses.  Some attributes are currently defined generically for variables. Other attributes are defined for variables on particular target systems.  Other attributes are available for functions (see Function Attributes) and for types (see Type Attributes). Other front ends might define more attributes (see Extensions to the C++ Language).

You may also specify attributes with __ preceding and following each keyword.  This allows you to use them in header files without being concerned about a possible macro of the same name.  For example, you may use __aligned__ instead of aligned.

See Attribute Syntax, for details of the exact syntax for using attributes.

aligned (ALIGNMENT)
     This attribute specifies a minimum alignment for the variable or structure field, measured in bytes.  For example, the declaration:

          int x __attribute__ ((aligned (16))) = 0;

     causes the compiler to allocate the global variable x on a 16-byte boundary.  On a 68040, this could be used in conjunction with an asm expression to access the move16 instruction which requires 16-byte aligned operands.

     You can also specify the alignment of structure fields.  For example, to create a double-word aligned int pair, you could write:

          struct foo { int x[2] __attribute__ ((aligned (8))); };

     This is an alternative to creating a union with a double member that forces the union to be double-word aligned.

     As in the preceding examples, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given variable or structure field.  Alternatively, you can leave out the alignment factor and just ask the compiler to align a variable or field to the maximum useful alignment for the target machine you are compiling for.  For example, you could write:

          short array[3] __attribute__ ((aligned));

     Whenever you leave out the alignment factor in an aligned attribute specification, the compiler automatically sets the alignment for the declared variable or field to the largest alignment which is ever used for any data type on the target machine you are compiling for.  Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables or fields that you have aligned this way.

     The aligned attribute can only increase the alignment; but you can decrease it by specifying packed as well.  See below.

     Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker.  On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment.  (For some linkers, the maximum supported alignment may be very very small.)  If your linker is only able to align variables up to a maximum of 8 byte alignment, then specifying aligned(16) in an __attribute__ will still only provide you with 8 byte alignment.  See your linker documentation for further information.

cleanup (CLEANUP_FUNCTION)
     The cleanup attribute runs a function when the variable goes out of scope.  This attribute can only be applied to auto function scope variables; it may not be applied to parameters or variables with static storage duration.  The function must take one parameter, a pointer to a type compatible with the variable.  The return value of the function (if any) is ignored.

     If -fexceptions is enabled, then CLEANUP_FUNCTION will be run during the stack unwinding that happens during the processing of the exception.  Note that the cleanup attribute does not allow the exception to be caught, only to perform an action. It is undefined what happens if CLEANUP_FUNCTION does not return normally.

common
nocommon
     The common attribute requests GCC to place a variable in ``common'' storage.  The nocommon attribute requests the opposite---to allocate space for it directly.

     These attributes override the default chosen by the -fno-common and -fcommon flags respectively.

deprecated
     The deprecated attribute results in a warning if the variable is used anywhere in the source file.  This is useful when identifying variables that are expected to be removed in a future version of a program.  The warning also includes the location of the declaration of the deprecated variable, to enable users to easily find further information about why the variable is deprecated, or what they should do instead.  Note that the warning only occurs for uses:

          extern int old_var __attribute__ ((deprecated));
          extern int old_var;
          int new_fn () { return old_var; }

     results in a warning on line 3 but not line 2.

     The deprecated attribute can also be used for functions and types (see Function Attributes, see Type Attributes.)

mode (MODE)
     This attribute specifies the data type for the declaration---whichever type corresponds to the mode MODE.  This in effect lets you request an integer or floating point type according to its width.

     You may also specify a mode of byte or __byte__ to indicate the mode corresponding to a one-byte integer, word or __word__ for the mode of a one-word integer, and pointer or __pointer__ for the mode used to represent pointers.

packed
     The packed attribute specifies that a variable or structure field should have the smallest possible alignment---one byte for a variable, and one bit for a field, unless you specify a larger value with the aligned attribute.

     Here is a structure in which the field x is packed, so that it immediately follows a:

          struct foo
          {
            char a;
            int x[2] __attribute__ ((packed));
          };

section ("SECTION-NAME")
     Normally, the compiler places the objects it generates in sections like data and bss.  Sometimes, however, you need additional sections, or you need certain particular variables to appear in special sections, for example to map to special hardware.  The section attribute specifies that a variable (or function) lives in a particular section.  For example, this small program uses several specific section names:

          struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
          struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
          char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
          int init_data __attribute__ ((section ("INITDATA"))) = 0;

          main()
          {
            /* Initialize stack pointer */
            init_sp (stack + sizeof (stack));

            /* Initialize initialized data */
            memcpy (&init_data, &data, &edata - &data);

            /* Turn on the serial ports */
            init_duart (&a);
            init_duart (&b);
          }

     Use the section attribute with an initialized definition of a global variable, as shown in the example.  GCC issues a warning and otherwise ignores the section attribute in uninitialized variable declarations.

     You may only use the section attribute with a fully initialized global definition because of the way linkers work.  The linker requires each object be defined once, with the exception that uninitialized variables tentatively go in the common (or bss) section and can be multiply ``defined''.  You can force a variable to be initialized with the -fno-common flag or the nocommon attribute.

     Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

shared
     On Microsoft Windows, in addition to putting variable definitions in a named section, the section can also be shared among all running copies of an executable or DLL.  For example, this small program defines shared data by putting it in a named section shared and marking the section shareable:

          int foo __attribute__((section ("shared"), shared)) = 0;

          int
          main()
          {
            /* Read and write foo.  All running
               copies see the same value.  */
            return 0;
          }

     You may only use the shared attribute along with section attribute with a fully initialized global definition because of the way linkers work.  See section attribute for more information.

     The shared attribute is only available on Microsoft Windows.

tls_model ("TLS_MODEL")
     The tls_model attribute sets thread-local storage model (see Thread-Local) of a particular __thread variable, overriding -ftls-model= command line switch on a per-variable basis. The TLS_MODEL argument should be one of global-dynamic, local-dynamic, initial-exec or local-exec.

     Not all targets support this attribute.

unused
     This attribute, attached to a variable, means that the variable is meant to be possibly unused.  GCC will not produce a warning for this variable.

used
     This attribute, attached to a variable, means that the variable must be emitted even if it appears that the variable is not referenced.

vector_size (BYTES)
     This attribute specifies the vector size for the variable, measured in bytes.  For example, the declaration:

          int foo __attribute__ ((vector_size (16)));

     causes the compiler to set the mode for foo, to be 16 bytes, divided into int sized units.  Assuming a 32-bit int (a vector of 4 units of 4 bytes), the corresponding mode of foo will be V4SI.

     This attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.

     Aggregates with this attribute are invalid, even if they are of the same size as a corresponding scalar.  For example, the declaration:

          struct S { int a; };
          struct S  __attribute__ ((vector_size (16))) foo;

     is invalid even if the size of the structure is the same as the size of the int.

selectany
     The selectany attribute causes an initialized global variable to have link-once semantics.  When multiple definitions of the variable are encountered by the linker, the first is selected and the remainder are discarded.  Following usage by the Microsoft compiler, the linker is told not to warn about size or content differences of the multiple definitions.

     Although the primary usage of this attribute is for POD types, the attribute can also be applied to global C++ objects that are initialized by a constructor.  In this case, the static initialization and destruction code for the object is emitted in each translation defining the object, but the calls to the constructor and destructor are protected by a link-once guard variable.

     The selectany attribute is only available on Microsoft Windows targets.  You can use __declspec (selectany) as a synonym for __attribute__ ((selectany)) for compatibility with other compilers.

weak
     The weak attribute is described in see Function Attributes.

dllimport
     The dllimport attribute is described in see Function Attributes.

dllexport
     The dllexport attribute is described in see Function Attributes.

M32R/D Variable Attributes
--------------------------

One attribute is currently defined for the M32R/D.

model (MODEL-NAME)
     Use this attribute on the M32R/D to set the addressability of an object. The identifier MODEL-NAME is one of small, medium, or large, representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction).

     Medium and large model objects may live anywhere in the 32-bit address space (the compiler will generate seth/add3 instructions to load their addresses).

i386 Variable Attributes
------------------------

Two attributes are currently defined for i386 configurations: ms_struct and gcc_struct

ms_struct
gcc_struct

     If packed is used on a structure, or if bit-fields are used it may be that the Microsoft ABI packs them differently than GCC would normally pack them.  Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.

     Currently -m[no-]ms-bitfields is provided for the Microsoft Windows X86 compilers to match the native Microsoft compiler.

     The Microsoft structure layout algorithm is fairly simple with the exception of the bitfield packing:

     The padding and alignment of members of structures and whether a bit field can straddle a storage-unit boundary

      1. Structure members are stored sequentially in the order in which they are declared: the first member has the lowest memory address and the last member the highest.

      2. Every data object has an alignment-requirement. The alignment-requirement for all data except structures, unions, and arrays is either the size of the object or the current packing size (specified with either the aligned attribute or the pack pragma), whichever is less. For structures,  unions, and arrays, the alignment-requirement is the largest alignment-requirement of its members. Every object is allocated an offset so that:

          offset %  alignment-requirement == 0

      3. Adjacent bit fields are packed into the same 1-, 2-, or 4-byte allocation unit if the integral types are the same size and if the next bit field fits into the current allocation unit without crossing the boundary imposed by the common alignment requirements of the bit fields.

     Handling of zero-length bitfields:

     MSVC interprets zero-length bitfields in the following ways:

      1. If a zero-length bitfield is inserted between two bitfields that would normally be coalesced, the bitfields will not be coalesced.

          For example:

               struct
                {
                  unsigned long bf_1 : 12;
                  unsigned long : 0;
                  unsigned long bf_2 : 12;
                } t1;

          The size of t1 would be 8 bytes with the zero-length bitfield.  If the zero-length bitfield were removed, t1's size would be 4 bytes.

      2. If a zero-length bitfield is inserted after a bitfield, foo, and the alignment of the zero-length bitfield is greater than the member that follows it, bar, bar will be aligned as the type of the zero-length bitfield.

          For example:

               struct
                {
                  char foo : 4;
                  short : 0;
                  char bar;
                } t2;

               struct
                {
                  char foo : 4;
                  short : 0;
                  double bar;
                } t3;

          For t2, bar will be placed at offset 2, rather than offset 1. Accordingly, the size of t2 will be 4.  For t3, the zero-length bitfield will not affect the alignment of bar or, as a result, the size of the structure.

          Taking this into account, it is important to note the following:

           1. If a zero-length bitfield follows a normal bitfield, the type of the zero-length bitfield may affect the alignment of the structure as whole. For example, t2 has a size of 4 bytes, since the zero-length bitfield follows a normal bitfield, and is of type short.

           2. Even if a zero-length bitfield is not followed by a normal bitfield, it may still affect the alignment of the structure:

                    struct
                     {
                       char foo : 6;
                       long : 0;
                     } t4;

               Here, t4 will take up 4 bytes.

      3. Zero-length bitfields following non-bitfield members are ignored:

               struct
                {
                  char foo;
                  long : 0;
                  char bar;
                } t5;

          Here, t5 will take up 2 bytes.

PowerPC Variable Attributes
---------------------------

Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.

For full documentation of the struct attributes please see the documentation in the see i386 Variable Attributes, section.

For documentation of altivec attribute please see the documentation in the see PowerPC Type Attributes, section.

Xstormy16 Variable Attributes
-----------------------------

One attribute is currently defined for xstormy16 configurations: below100

below100

     If a variable has the below100 attribute (BELOW100 is allowed also), GCC will place the variable in the first 0x100 bytes of memory and use special opcodes to access it.  Such variables will be placed in either the .bss_below100 section or the .data_below100 section.

Specifying Attributes of Types
==============================

The keyword __attribute__ allows you to specify special attributes of struct and union types when you define such types.  This keyword is followed by an attribute specification inside double parentheses.  Seven attributes are currently defined for types: aligned, packed, transparent_union, unused, deprecated, visibility, and may_alias.  Other attributes are defined for functions (see Function Attributes) and for variables (see Variable Attributes).

You may also specify any one of these attributes with __ preceding and following its keyword.  This allows you to use these attributes in header files without being concerned about a possible macro of the same name.  For example, you may use __aligned__ instead of aligned.

You may specify type attributes either in a typedef declaration or in an enum, struct or union type declaration or definition.

For an enum, struct or union type, you may specify attributes either between the enum, struct or union tag and the name of the type, or just past the closing curly brace of the definition.  The former syntax is preferred.

See Attribute Syntax, for details of the exact syntax for using attributes.

aligned (ALIGNMENT)
     This attribute specifies a minimum alignment (in bytes) for variables of the specified type.  For example, the declarations:

          struct S { short f[3]; } __attribute__ ((aligned (8)));
          typedef int more_aligned_int __attribute__ ((aligned (8)));

     force the compiler to insure (as far as it can) that each variable whose type is struct S or more_aligned_int will be allocated and aligned at least on a 8-byte boundary.  On a SPARC, having all variables of type struct S aligned to 8-byte boundaries allows the compiler to use the ldd and std (doubleword load and store) instructions when copying one variable of type struct S to another, thus improving run-time efficiency.

     Note that the alignment of any given struct or union type is required by the ISO C standard to be at least a perfect multiple of the lowest common multiple of the alignments of all of the members of the struct or union in question.  This means that you can effectively adjust the alignment of a struct or union type by attaching an aligned attribute to any one of the members of such a type, but the notation illustrated in the example above is a more obvious, intuitive, and readable way to request the compiler to adjust the alignment of an entire struct or union type.

     As in the preceding example, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given struct or union type.  Alternatively, you can leave out the alignment factor and just ask the compiler to align a type to the maximum useful alignment for the target machine you are compiling for.  For example, you could write:

          struct S { short f[3]; } __attribute__ ((aligned));

     Whenever you leave out the alignment factor in an aligned attribute specification, the compiler automatically sets the alignment for the type to the largest alignment which is ever used for any data type on the target machine you are compiling for.  Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables which have types that you have aligned this way.

     In the example above, if the size of each short is 2 bytes, then the size of the entire struct S type is 6 bytes.  The smallest power of two which is greater than or equal to that is 8, so the compiler sets the alignment for the entire struct S type to 8 bytes.

     Note that although you can ask the compiler to select a time-efficient alignment for a given type and then declare only individual stand-alone objects of that type, the compiler's ability to select a time-efficient alignment is primarily useful only when you plan to create arrays of variables having the relevant (efficiently aligned) type.  If you declare or use arrays of variables of an efficiently-aligned type, then it is likely that your program will also be doing pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type, and the code that the compiler generates for these pointer arithmetic operations will often be more efficient for efficiently-aligned types than for other types.

     The aligned attribute can only increase the alignment; but you can decrease it by specifying packed as well.  See below.

     Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker.  On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment.  (For some linkers, the maximum supported alignment may be very very small.)  If your linker is only able to align variables up to a maximum of 8 byte alignment, then specifying aligned(16) in an __attribute__ will still only provide you with 8 byte alignment.  See your linker documentation for further information.

packed
     This attribute, attached to struct or union type definition, specifies that each member (other than zero-width bitfields) of the structure or union is placed to minimize the memory required.  When attached to an enum definition, it indicates that the smallest integral type should be used.

     Specifying this attribute for struct and union types is equivalent to specifying the packed attribute on each of the structure or union members.  Specifying the -fshort-enums flag on the line is equivalent to specifying the packed attribute on all enum definitions.

     In the following example struct my_packed_struct's members are packed closely together, but the internal layout of its s member is not packed---to do that, struct my_unpacked_struct would need to be packed too.

          struct my_unpacked_struct
           {
              char c;
              int i;
           };

          struct __attribute__ ((__packed__)) my_packed_struct
            {
               char c;
               int  i;
               struct my_unpacked_struct s;
            };

     You may only specify this attribute on the definition of a enum, struct or union, not on a typedef which does not also define the enumerated type, structure or union.

transparent_union
     This attribute, attached to a union type definition, indicates that any function parameter having that union type causes calls to that function to be treated in a special way.

     First, the argument corresponding to a transparent union type can be of any type in the union; no cast is required.  Also, if the union contains a pointer type, the corresponding argument can be a null pointer constant or a void pointer expression; and if the union contains a void pointer type, the corresponding argument can be any pointer expression. If the union member type is a pointer, qualifiers like const on the referenced type must be respected, just as with normal pointer conversions.

     Second, the argument is passed to the function using the calling conventions of the first member of the transparent union, not the calling conventions of the union itself.  All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.

     Transparent unions are designed for library functions that have multiple interfaces for compatibility reasons.  For example, suppose the wait function must accept either a value of type int * to comply with Posix, or a value of type union wait * to comply with the 4.1BSD interface.  If wait's parameter were void *, wait would accept both kinds of arguments, but it would also accept any other pointer type and this would make argument type checking less useful.  Instead, <sys/wait.h> might define the interface as follows:

          typedef union
            {
              int *__ip;
              union wait *__up;
            } wait_status_ptr_t __attribute__ ((__transparent_union__));

          pid_t wait (wait_status_ptr_t);

     This interface allows either int * or union wait * arguments to be passed, using the int * calling convention. The program can call wait with arguments of either type:

          int w1 () { int w; return wait (&w); }
          int w2 () { union wait w; return wait (&w); }

     With this interface, wait's implementation might look like this:

          pid_t wait (wait_status_ptr_t p)
          {
            return waitpid (-1, p.__ip, 0);
          }

unused
     When attached to a type (including a union or a struct), this attribute means that variables of that type are meant to appear possibly unused.  GCC will not produce a warning for any variables of that type, even if the variable appears to do nothing.  This is often the case with lock or thread classes, which are usually defined and then not referenced, but contain constructors and destructors that have nontrivial bookkeeping functions.

deprecated
     The deprecated attribute results in a warning if the type is used anywhere in the source file.  This is useful when identifying types that are expected to be removed in a future version of a program. If possible, the warning also includes the location of the declaration of the deprecated type, to enable users to easily find further information about why the type is deprecated, or what they should do instead.  Note that the warnings only occur for uses and then only if the type is being applied to an identifier that itself is not being declared as deprecated.

          typedef int T1 __attribute__ ((deprecated));
          T1 x;
          typedef T1 T2;
          T2 y;
          typedef T1 T3 __attribute__ ((deprecated));
          T3 z __attribute__ ((deprecated));

     results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No warning is issued for line 4 because T2 is not explicitly deprecated.  Line 5 has no warning because T3 is explicitly deprecated.  Similarly for line 6.

     The deprecated attribute can also be used for functions and variables (see Function Attributes, see Variable Attributes.)

may_alias
     Accesses to objects with types with this attribute are not subjected to type-based alias analysis, but are instead assumed to be able to alias any other type of objects, just like the char type.  See -fstrict-aliasing for more information on aliasing issues.

     Example of use:

          typedef short __attribute__((__may_alias__)) short_a;

          int
          main (void)
          {
            int a = 0x12345678;
            short_a *b = (short_a *) &a;

            b[1] = 0;

            if (a == 0x12345678)
              abort();

            exit(0);
          }

     If you replaced short_a with short in the variable declaration, the above program would abort when compiled with -fstrict-aliasing, which is on by default at -O2 or above in recent GCC versions.

visibility
     In C++, attribute visibility (see Function Attributes) can also be applied to class, struct, union and enum types.  Unlike other type attributes, the attribute must appear between the initial keyword and the name of the type; it cannot appear after the body of the type.

     Note that the type visibility is applied to vague linkage entities associated with the class (vtable, typeinfo node, etc.).  In particular, if a class is thrown as an exception in one shared object and caught in another, the class must have default visibility. Otherwise the two shared objects will be unable to use the same typeinfo node and exception handling will break.

ARM Type Attributes
-------------------

On those ARM targets that support dllimport (such as Symbian OS), you can use the notshared attribute to indicate that the virtual table and other similar data for a class should not be exported from a DLL.  For example:

     class __declspec(notshared) C {
     public:
       __declspec(dllimport) C();
       virtual void f();
     }

     __declspec(dllexport)
     C::C() {}

In this code, C::C is exported from the current DLL, but the virtual table for C is not exported.  (You can use __attribute__ instead of __declspec if you prefer, but most Symbian OS code uses __declspec.)

i386 Type Attributes
--------------------

Two attributes are currently defined for i386 configurations: ms_struct and gcc_struct

ms_struct
gcc_struct

If packed is used on a structure, or if bit-fields are used it may be that the Microsoft ABI packs them differently than GCC would normally pack them.  Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.

Currently -m[no-]ms-bitfields is provided for the Microsoft Windows X86 compilers to match the native Microsoft compiler.

To specify multiple attributes, separate them by commas within the double parentheses: for example, __attribute__ ((aligned (16), packed)).

PowerPC Type Attributes
-----------------------

Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.

For full documentation of the struct attributes please see the documentation in the see i386 Type Attributes, section.

The altivec attribute allows one to declare AltiVec vector data types supported by the AltiVec Programming Interface Manual.  The attribute requires an argument to specify one of three vector types: vector__, pixel__ (always followed by unsigned short), and bool__ (always followed by unsigned).

     __attribute__((altivec(vector__)))
     __attribute__((altivec(pixel__))) unsigned short
     __attribute__((altivec(bool__))) unsigned

These attributes mainly are intended to support the __vector, __pixel, and __bool AltiVec keywords.

An Inline Function is As Fast As a Macro
========================================

By declaring a function inline, you can direct GCC to integrate that function's code into the code for its callers.  This makes execution faster by eliminating the function-call overhead; in addition, if any of the actual argument values are constant, their known values may permit simplifications at compile time so that not all of the inline function's code needs to be included.  The effect on code size is less predictable; object code may be larger or smaller with function inlining, depending on the particular case.  Inlining of functions is an optimization and it really ``works'' only in optimizing compilation.  If you don't use -O, no function is really inline.

Inline functions are included in the ISO C99 standard, but there are currently substantial differences between what GCC implements and what the ISO C99 standard requires.  GCC will fully support C99 inline functions in version 4.3.  The traditional GCC handling of inline functions will still be available with -std=gnu89, -fgnu89-inline or when gnu_inline attribute is present on all inline declarations.  The preprocessor macros __GNUC_GNU_INLINE__ and __GNUC_STDC_INLINE__ may be used to determine the handling of inline during a particular compilation (see Common Predefined Macros (The C Preprocessor)).

To declare a function inline, use the inline keyword in its declaration, like this:

     inline int
     inc (int *a)
     {
       (*a)++;
     }

(If you are writing a header file to be included in ISO C programs, write __inline__ instead of inline.  See Alternate Keywords.) You can also make all ``simple enough'' functions inline with the option -finline-functions.

Note that certain usages in a function definition can make it unsuitable for inline substitution.  Among these usages are: use of varargs, use of alloca, use of variable sized data types (see Variable Length), use of computed goto (see Labels as Values), use of nonlocal goto, and nested functions (see Nested Functions).  Using -Winline will warn when a function marked inline could not be substituted, and will give the reason for the failure.

Note that in C and Objective-C, unlike C++, the inline keyword does not affect the linkage of the function.

GCC automatically inlines member functions defined within the class body of C++ programs even if they are not explicitly declared inline.  (You can override this with -fno-default-inline; see Options Controlling C++ Dialect.)

When a function is both inline and static, if all calls to the function are integrated into the caller, and the function's address is never used, then the function's own assembler code is never referenced. In this case, GCC does not actually output assembler code for the function, unless you specify the option -fkeep-inline-functions. Some calls cannot be integrated for various reasons (in particular, calls that precede the function's definition cannot be integrated, and neither can recursive calls within the definition).  If there is a nonintegrated call, then the function is compiled to assembler code as usual.  The function must also be compiled as usual if the program refers to its address, because that can't be inlined.

When an inline function is not static, then the compiler must assume that there may be calls from other source files; since a global symbol can be defined only once in any program, the function must not be defined in the other source files, so the calls therein cannot be integrated. Therefore, a non-static inline function is always compiled on its own in the usual fashion.

If you specify both inline and extern in the function definition, then the definition is used only for inlining.  In no case is the function compiled on its own, not even if you refer to its address explicitly.  Such an address becomes an external reference, as if you had only declared the function, and had not defined it.

This combination of inline and extern has almost the effect of a macro.  The way to use it is to put a function definition in a header file with these keywords, and put another copy of the definition (lacking inline and extern) in a library file. The definition in the header file will cause most calls to the function to be inlined.  If any uses of the function remain, they will refer to the single copy in the library.

Since GCC 4.3 will implement ISO C99 semantics for inline functions, it is simplest to use static inline only to guarantee compatibility.  (The existing semantics will remain available when -std=gnu89 is specified, but eventually the default will be -std=gnu99; that will implement the C99 semantics, though it does not do so in versions of GCC before 4.3.  After the default changes, the existing semantics will still be available via the -fgnu89-inline option or the gnu_inline function attribute.)

GCC does not inline any functions when not optimizing unless you specify the always_inline attribute for the function, like this:

     /* Prototype.  */
     inline void foo (const char) __attribute__((always_inline));

Assembler Instructions with C Expression Operands
=================================================

In an assembler instruction using asm, you can specify the operands of the instruction using C expressions.  This means you need not guess which registers or memory locations will contain the data you want to use.

You must specify an assembler instruction template much like what appears in a machine description, plus an operand constraint string for each operand.

For example, here is how to use the 68881's fsinx instruction:

     asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));

Here angle is the C expression for the input operand while result is that of the output operand.  Each has "f" as its operand constraint, saying that a floating point register is required. The = in =f indicates that the operand is an output; all output operands' constraints must use =.  The constraints use the same language used in the machine description (see Constraints).

Each operand is described by an operand-constraint string followed by the C expression in parentheses.  A colon separates the assembler template from the first output operand and another separates the last output operand from the first input, if any.  Commas separate the operands within each group.  The total number of operands is currently limited to 30; this limitation may be lifted in some future version of GCC.

If there are no output operands but there are input operands, you must place two consecutive colons surrounding the place where the output operands would go.

As of GCC version 3.1, it is also possible to specify input and output operands using symbolic names which can be referenced within the assembler code.  These names are specified inside square brackets preceding the constraint string, and can be referenced inside the assembler code using %[NAME] instead of a percentage sign followed by the operand number.  Using named operands the above example could look like:

     asm ("fsinx %[angle],%[output]"
          : [output] "=f" (result)
          : [angle] "f" (angle));

Note that the symbolic operand names have no relation whatsoever to other C identifiers.  You may use any name you like, even those of existing C symbols, but you must ensure that no two operands within the same assembler construct use the same symbolic name.

Output operand expressions must be lvalues; the compiler can check this. The input operands need not be lvalues.  The compiler cannot check whether the operands have data types that are reasonable for the instruction being executed.  It does not parse the assembler instruction template and does not know what it means or even whether it is valid assembler input.  The extended asm feature is most often used for machine instructions the compiler itself does not know exist.  If the output expression cannot be directly addressed (for example, it is a bit-field), your constraint must allow a register.  In that case, GCC will use the register as the output of the asm, and then store that register into the output.

The ordinary output operands must be write-only; GCC will assume that the values in these operands before the instruction are dead and need not be generated.  Extended asm supports input-output or read-write operands.  Use the constraint character + to indicate such an operand and list it with the output operands.  You should only use read-write operands when the constraints for the operand (or the operand in which only some of the bits are to be changed) allow a register.

You may, as an alternative, logically split its function into two separate operands, one input operand and one write-only output operand.  The connection between them is expressed by constraints which say they need to be in the same location when the instruction executes.  You can use the same C expression for both operands, or different expressions.  For example, here we write the (fictitious) combine instruction with bar as its read-only source operand and foo as its read-write destination:

     asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));

The constraint "0" for operand 1 says that it must occupy the same location as operand 0.  A number in constraint is allowed only in an input operand and it must refer to an output operand.

Only a number in the constraint can guarantee that one operand will be in the same place as another.  The mere fact that foo is the value of both operands is not enough to guarantee that they will be in the same place in the generated assembler code.  The following would not work reliably:

     asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));

Various optimizations or reloading could cause operands 0 and 1 to be in different registers; GCC knows no reason not to do so.  For example, the compiler might find a copy of the value of foo in one register and use it for operand 1, but generate the output operand 0 in a different register (copying it afterward to foo's own address).  Of course, since the register for operand 1 is not even mentioned in the assembler code, the result will not work, but GCC can't tell that.

As of GCC version 3.1, one may write [NAME] instead of the operand number for a matching constraint.  For example:

     asm ("cmoveq %1,%2,%[result]"
          : [result] "=r"(result)
          : "r" (test), "r"(new), "[result]"(old));

Sometimes you need to make an asm operand be a specific register, but there's no matching constraint letter for that register by itself.  To force the operand into that register, use a local variable for the operand and specify the register in the variable declaration. See Explicit Reg Vars.  Then for the asm operand, use any register constraint letter that matches the register:

     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = ...;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

In the above example, beware that a register that is call-clobbered by the target ABI will be overwritten by any function call in the assignment, including library calls for arithmetic operators. Assuming it is a call-clobbered register, this may happen to r0 above by the assignment to p2.  If you have to use such a register, use temporary variables for expressions between the register assignment and use:

     int t1 = ...;
     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = t1;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

Some instructions clobber specific hard registers.  To describe this, write a third colon after the input operands, followed by the names of the clobbered hard registers (given as strings).  Here is a realistic example for the VAX:

     asm volatile ("movc3 %0,%1,%2"
                   : /* no outputs */
                   : "g" (from), "g" (to), "g" (count)
                   : "r0", "r1", "r2", "r3", "r4", "r5");

You may not write a clobber description in a way that overlaps with an input or output operand.  For example, you may not have an operand describing a register class with one member if you mention that register in the clobber list.  Variables declared to live in specific registers (see Explicit Reg Vars), and used as asm input or output operands must have no part mentioned in the clobber description. There is no way for you to specify that an input operand is modified without also specifying it as an output operand.  Note that if all the output operands you specify are for this purpose (and hence unused), you will then also need to specify volatile for the asm construct, as described below, to prevent GCC from deleting the asm statement as unused.

If you refer to a particular hardware register from the assembler code, you will probably have to list the register after the third colon to tell the compiler the register's value is modified.  In some assemblers, the register names begin with %; to produce one % in the assembler code, you must write %% in the input.

If your assembler instruction can alter the condition code register, add cc to the list of clobbered registers.  GCC on some machines represents the condition codes as a specific hardware register; cc serves to name this register.  On other machines, the condition code is handled differently, and specifying cc has no effect.  But it is valid no matter what the machine.

If your assembler instructions access memory in an unpredictable fashion, add memory to the list of clobbered registers.  This will cause GCC to not keep memory values cached in registers across the assembler instruction and not optimize stores or loads to that memory. You will also want to add the volatile keyword if the memory affected is not listed in the inputs or outputs of the asm, as the memory clobber does not count as a side-effect of the asm.  If you know how large the accessed memory is, you can add it as input or output but if this is not known, you should add memory.  As an example, if you access ten bytes of a string, you can use a memory input like:

     {"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.

Note that in the following example the memory input is necessary, otherwise GCC might optimize the store to x away:

     int foo ()
     {
       int x = 42;
       int *y = &x;
       int result;
       asm ("magic stuff accessing an 'int' pointed to by '%1'"
             "=&d" (r) : "a" (y), "m" (*y));
       return result;
     }

You can put multiple assembler instructions together in a single asm template, separated by the characters normally used in assembly code for the system.  A combination that works in most places is a newline to break the line, plus a tab character to move to the instruction field (written as \n\t).  Sometimes semicolons can be used, if the assembler allows semicolons as a line-breaking character.  Note that some assembler dialects use semicolons to start a comment. The input operands are guaranteed not to use any of the clobbered registers, and neither will the output operands' addresses, so you can read and write the clobbered registers as many times as you like.  Here is an example of multiple instructions in a template; it assumes the subroutine _foo accepts arguments in registers 9 and 10:

     asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
          : /* no outputs */
          : "g" (from), "g" (to)
          : "r9", "r10");

Unless an output operand has the & constraint modifier, GCC may allocate it in the same register as an unrelated input operand, on the assumption the inputs are consumed before the outputs are produced. This assumption may be false if the assembler code actually consists of more than one instruction.  In such a case, use & for each output operand that may not overlap an input.  See Modifiers.

If you want to test the condition code produced by an assembler instruction, you must include a branch and a label in the asm construct, as follows:

     asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
          : "g" (result)
          : "g" (input));

This assumes your assembler supports local labels, as the GNU assembler and most Unix assemblers do.

Speaking of labels, jumps from one asm to another are not supported.  The compiler's optimizers do not know about these jumps, and therefore they cannot take account of them when deciding how to optimize.

Usually the most convenient way to use these asm instructions is to encapsulate them in macros that look like functions.  For example,

     #define sin(x)       \
     ({ double __value, __arg = (x);   \
        asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
        __value; })

Here the variable __arg is used to make sure that the instruction operates on a proper double value, and to accept only those arguments x which can convert automatically to a double.

Another way to make sure the instruction operates on the correct data type is to use a cast in the asm.  This is different from using a variable __arg in that it converts more different types.  For example, if the desired type were int, casting the argument to int would accept a pointer with no complaint, while assigning the argument to an int variable named __arg would warn about using a pointer unless the caller explicitly casts it.

If an asm has output operands, GCC assumes for optimization purposes the instruction has no side effects except to change the output operands.  This does not mean instructions with a side effect cannot be used, but you must be careful, because the compiler may eliminate them if the output operands aren't used, or move them out of loops, or replace two with one if they constitute a common subexpression.  Also, if your instruction does have a side effect on a variable that otherwise appears not to change, the old value of the variable may be reused later if it happens to be found in a register.

You can prevent an asm instruction from being deleted by writing the keyword volatile after the asm.  For example:

     #define get_and_set_priority(new)              \
     ({ int __old;                                  \
        asm volatile ("get_and_set_priority %0, %1" \
                      : "=g" (__old) : "g" (new));  \
        __old; })

The volatile keyword indicates that the instruction has important side-effects.  GCC will not delete a volatile asm if it is reachable.  (The instruction can still be deleted if GCC can prove that control-flow will never reach the location of the instruction.)  Note that even a volatile asm instruction can be moved relative to other code, including across jump instructions.  For example, on many targets there is a system register which can be set to control the rounding mode of floating point operations.  You might try setting it with a volatile asm, like this PowerPC example:

            asm volatile("mtfsf 255,%0" : : "f" (fpenv));
            sum = x + y;

This will not work reliably, as the compiler may move the addition back before the volatile asm.  To make it work you need to add an artificial dependency to the asm referencing a variable in the code you don't want moved, for example:

         asm volatile ("mtfsf 255,%1" : "=X"(sum): "f"(fpenv));
         sum = x + y;

Similarly, you can't expect a sequence of volatile asm instructions to remain perfectly consecutive.  If you want consecutive output, use a single asm. Also, GCC will perform some optimizations across a volatile asm instruction; GCC does not ``forget everything'' when it encounters a volatile asm instruction the way some other compilers do.

An asm instruction without any output operands will be treated identically to a volatile asm instruction.

It is a natural idea to look for a way to give access to the condition code left by the assembler instruction.  However, when we attempted to implement this, we found no way to make it work reliably.  The problem is that output operands might need reloading, which would result in additional following ``store'' instructions.  On most machines, these instructions would alter the condition code before there was time to test it.  This problem doesn't arise for ordinary ``test'' and ``compare'' instructions because they don't have any output operands.

For reasons similar to those described above, it is not possible to give an assembler instruction access to the condition code left by previous instructions.

If you are writing a header file that should be includable in ISO C programs, write __asm__ instead of asm.  See Alternate Keywords.

Size of an asm
--------------

Some targets require that GCC track the size of each instruction used in order to generate correct code.  Because the final length of an asm is only known by the assembler, GCC must make an estimate as to how big it will be.  The estimate is formed by counting the number of statements in the pattern of the asm and multiplying that by the length of the longest instruction on that processor.  Statements in the asm are identified by newline characters and whatever statement separator characters are supported by the assembler; on most processors this is the `;' character.

Normally, GCC's estimate is perfectly adequate to ensure that correct code is generated, but it is possible to confuse the compiler if you use pseudo instructions or assembler macros that expand into multiple real instructions or if you use assembler directives that expand to more space in the object file than would be needed for a single instruction. If this happens then the assembler will produce a diagnostic saying that a label is unreachable.

i386 floating point asm operands
--------------------------------

There are several rules on the usage of stack-like regs in asm_operands insns.  These rules apply only to the operands that are stack-like regs:

 1. Given a set of input regs that die in an asm_operands, it is necessary to know which are implicitly popped by the asm, and which must be explicitly popped by gcc.

     An input reg that is implicitly popped by the asm must be explicitly clobbered, unless it is constrained to match an output operand.

 2. For any input reg that is implicitly popped by an asm, it is necessary to know how to adjust the stack to compensate for the pop. If any non-popped input is closer to the top of the reg-stack than the implicitly popped reg, it would not be possible to know what the stack looked like---it's not clear how the rest of the stack ``slides up''.

     All implicitly popped input regs must be closer to the top of the reg-stack than any input that is not implicitly popped.

     It is possible that if an input dies in an insn, reload might use the input reg for an output reload.  Consider this example:

          asm ("foo" : "=t" (a) : "f" (b));

     This asm says that input B is not popped by the asm, and that the asm pushes a result onto the reg-stack, i.e., the stack is one deeper after the asm than it was before.  But, it is possible that reload will think that it can use the same reg for both the input and the output, if input B dies in this insn.

     If any input operand uses the f constraint, all output reg constraints must use the & earlyclobber.

     The asm above would be written as

          asm ("foo" : "=&t" (a) : "f" (b));

 3. Some operands need to be in particular places on the stack.  All output operands fall in this category---there is no other way to know which regs the outputs appear in unless the user indicates this in the constraints.

     Output operands must specifically indicate which reg an output appears in after an asm.  =f is not allowed: the operand constraints must select a class with a single reg.

 4. Output operands may not be ``inserted'' between existing stack regs. Since no 387 opcode uses a read/write operand, all output operands are dead before the asm_operands, and are pushed by the asm_operands. It makes no sense to push anywhere but the top of the reg-stack.

     Output operands must start at the top of the reg-stack: output operands may not ``skip'' a reg.

 5. Some asm statements may need extra stack space for internal calculations.  This can be guaranteed by clobbering stack registers unrelated to the inputs and outputs.

Here are a couple of reasonable asms to want to write.  This asm takes one input, which is internally popped, and produces two outputs.

     asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

This asm takes two inputs, which are popped by the fyl2xp1 opcode, and replaces them with one output.  The user must code the st(1) clobber for reg-stack.c to know that fyl2xp1 pops both inputs.

     asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");

     [file md.texi not included]

Controlling Names Used in Assembler Code
========================================

You can specify the name to be used in the assembler code for a C function or variable by writing the asm (or __asm__) keyword after the declarator as follows:

     int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable foo in the assembler code should be myfoo rather than the usual _foo.

On systems where an underscore is normally prepended to the name of a C function or variable, this feature allows you to define names for the linker that do not start with an underscore.

It does not make sense to use this feature with a non-static local variable since such variables do not have assembler names.  If you are trying to put the variable in a particular register, see Explicit Reg Vars.  GCC presently accepts such code with a warning, but will probably be changed to issue an error, rather than a warning, in the future.

You cannot use asm in this way in a function definition; but you can get the same effect by writing a declaration for the function before its definition and putting asm there, like this:

     extern func () asm ("FUNC");

     func (x, y)
          int x, y;
     /* ... */

It is up to you to make sure that the assembler names you choose do not conflict with any other assembler symbols.  Also, you must not use a register name; that would produce completely invalid assembler code.  GCC does not as yet have the ability to store static variables in registers. Perhaps that will be added.

Variables in Specified Registers
================================

GNU C allows you to put a few global variables into specified hardware registers.  You can also specify the register in which an ordinary register variable should be allocated.

  * Global register variables reserve registers throughout the program. This may be useful in programs such as programming language interpreters which have a couple of global variables that are accessed very often.

  * Local register variables in specific registers do not reserve the registers, except at the point where they are used as input or output operands in an asm statement and the asm statement itself is not deleted.  The compiler's data flow analysis is capable of determining where the specified registers contain live values, and where they are available for other uses.  Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis.  References to local register variables may be deleted or moved or simplified.

     These local variables are sometimes convenient for use with the extended asm feature (see Extended Asm), if you want to write one output of the assembler instruction directly into a particular register. (This will work provided the register you specify fits the constraints specified for that operand in the asm.)

Defining Global Register Variables
----------------------------------

You can define a global register variable in GNU C like this:

     register int *foo asm ("a5");

Here a5 is the name of the register which should be used.  Choose a register which is normally saved and restored by function calls on your machine, so that library routines will not clobber it.

Naturally the register name is cpu-dependent, so you would need to conditionalize your program according to cpu type.  The register a5 would be a good choice on a 68000 for a variable of pointer type.  On machines with register windows, be sure to choose a ``global'' register that is not affected magically by the function call mechanism.

In addition, operating systems on one type of cpu may differ in how they name the registers; then you would need additional conditionals.  For example, some 68000 operating systems call this register %a5.

Eventually there may be a way of asking the compiler to choose a register automatically, but first we need to figure out how it should choose and how to enable you to guide the choice.  No solution is evident.

Defining a global register variable in a certain register reserves that register entirely for this use, at least within the current compilation. The register will not be allocated for any other purpose in the functions in the current compilation.  The register will not be saved and restored by these functions.  Stores into this register are never deleted even if they would appear to be dead, but references may be deleted or moved or simplified.

It is not safe to access the global register variables from signal handlers, or from more than one thread of control, because the system library routines may temporarily use the register for other things (unless you recompile them specially for the task at hand).

It is not safe for one function that uses a global register variable to call another such function foo by way of a third function lose that was compiled without knowledge of this variable (i.e. in a different source file in which the variable wasn't declared).  This is because lose might save the register and put some other value there. For example, you can't expect a global register variable to be available in the comparison-function that you pass to qsort, since qsort might have put something else in that register.  (If you are prepared to recompile qsort with the same global register variable, you can solve this problem.)

If you want to recompile qsort or other source files which do not actually use your global register variable, so that they will not use that register for any other purpose, then it suffices to specify the compiler option -ffixed-REG.  You need not actually add a global register declaration to their source code.

A function which can alter the value of a global register variable cannot safely be called from a function compiled without this variable, because it could clobber the value the caller expects to find there on return. Therefore, the function which is the entry point into the part of the program that uses the global register variable must explicitly save and restore the value which belongs to its caller.

On most machines, longjmp will restore to each global register variable the value it had at the time of the setjmp.  On some machines, however, longjmp will not change the value of global register variables.  To be portable, the function that called setjmp should make other arrangements to save the values of the global register variables, and to restore them in a longjmp.  This way, the same thing will happen regardless of what longjmp does.

All global register variable declarations must precede all function definitions.  If such a declaration could appear after function definitions, the declaration would be too late to prevent the register from being used for other purposes in the preceding functions.

Global register variables may not have initial values, because an executable file has no means to supply initial contents for a register.

On the SPARC, there are reports that g3 ... g7 are suitable registers, but certain library functions, such as getwd, as well as the subroutines for division and remainder, modify g3 and g4.  g1 and g2 are local temporaries.

On the 68000, a2 ... a5 should be suitable, as should d2 ... d7. Of course, it will not do to use more than a few of those.

Specifying Registers for Local Variables
----------------------------------------

You can define a local register variable with a specified register like this:

     register int *foo asm ("a5");

Here a5 is the name of the register which should be used.  Note that this is the same syntax used for defining global register variables, but for a local variable it would appear within a function.

Naturally the register name is cpu-dependent, but this is not a problem, since specific registers are most often useful with explicit assembler instructions (see Extended Asm).  Both of these things generally require that you conditionalize your program according to cpu type.

In addition, operating systems on one type of cpu may differ in how they name the registers; then you would need additional conditionals.  For example, some 68000 operating systems call this register %a5.

Defining such a register variable does not reserve the register; it remains available for other uses in places where flow control determines the variable's value is not live.

This option does not guarantee that GCC will generate code that has this variable in the register you specify at all times.  You may not code an explicit reference to this register in the assembler instruction template part of an asm statement and assume it will always refer to this variable.  However, using the variable as an asm operand guarantees that the specified register is used for the operand.

Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis.  References to local register variables may be deleted or moved or simplified.

As for global register variables, it's recommended that you choose a register which is normally saved and restored by function calls on your machine, so that library routines will not clobber it.  A common pitfall is to initialize multiple call-clobbered registers with arbitrary expressions, where a function call or library call for an arithmetic operator will overwrite a register value from a previous assignment, for example r0 below:

     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = ...;

In those cases, a solution is to use a temporary variable for each arbitrary expression.   See Example of asm with clobbered asm reg.

Alternate Keywords
==================

-ansi and the various -std options disable certain keywords.  This causes trouble when you want to use GNU C extensions, or a general-purpose header file that should be usable by all programs, including ISO C programs.  The keywords asm, typeof and inline are not available in programs compiled with -ansi or -std (although inline can be used in a program compiled with -std=c99).  The ISO C99 keyword restrict is only available when -std=gnu99 (which will eventually be the default) or -std=c99 (or the equivalent -std=iso9899:1999) is used.

The way to solve these problems is to put __ at the beginning and end of each problematical keyword.  For example, use __asm__ instead of asm, and __inline__ instead of inline.

Other C compilers won't accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords.  It looks like this:

     #ifndef __GNUC__
     #define __asm__ asm
     #endif

-pedantic and other options cause warnings for many GNU C extensions. You can prevent such warnings within one expression by writing __extension__ before the expression.  __extension__ has no effect aside from this.

Incomplete enum Types
=====================

You can define an enum tag without specifying its possible values. This results in an incomplete type, much like what you get if you write struct foo without describing the elements.  A later declaration which does specify the possible values completes the type.

You can't allocate variables or storage using the type while it is incomplete.  However, you can work with pointers to that type.

This extension may not be very useful, but it makes the handling of enum more consistent with the way struct and union are handled.

This extension is not supported by GNU C++.

Function Names as Strings
=========================

GCC provides three magic variables which hold the name of the current function, as a string.  The first of these is __func__, which is part of the C99 standard:

     The identifier __func__ is implicitly declared by the translator
     as if, immediately following the opening brace of each function
     definition, the declaration

          static const char __func__[] = "function-name";

     appeared, where function-name is the name of the lexically-enclosing
     function.  This name is the unadorned name of the function.

__FUNCTION__ is another name for __func__.  Older versions of GCC recognize only this name.  However, it is not standardized.  For maximum portability, we recommend you use __func__, but provide a fallback definition with the preprocessor:

     #if __STDC_VERSION__ < 199901L
     # if __GNUC__ >= 2
     #  define __func__ __FUNCTION__
     # else
     #  define __func__ "<unknown>"
     # endif
     #endif

In C, __PRETTY_FUNCTION__ is yet another name for __func__.  However, in C++, __PRETTY_FUNCTION__ contains the type signature of the function as well as its bare name.  For example, this program:

     extern "C" {
     extern int printf (char *, ...);
     }

     class a {
      public:
       void sub (int i)
         {
           printf ("__FUNCTION__ = %s\n", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
         }
     };

     int
     main (void)
     {
       a ax;
       ax.sub (0);
       return 0;
     }

gives this output:

     __FUNCTION__ = sub
     __PRETTY_FUNCTION__ = void a::sub(int)

These identifiers are not preprocessor macros.  In GCC 3.3 and earlier, in C only, __FUNCTION__ and __PRETTY_FUNCTION__ were treated as string literals; they could be used to initialize char arrays, and they could be concatenated with other string literals.  GCC 3.4 and later treat them as variables, like __func__.  In C++, __FUNCTION__ and __PRETTY_FUNCTION__ have always been variables.

Getting the Return or Frame Address of a Function
=================================================

These functions may be used to get information about the callers of a function.

 -- Built-in Function: void * __builtin_return_address (unsigned int LEVEL)
     This function returns the return address of the current function, or of one of its callers.  The LEVEL argument is number of frames to scan up the call stack.  A value of 0 yields the return address of the current function, a value of 1 yields the return address of the caller of the current function, and so forth.  When inlining the expected behavior is that the function will return the address of the function that will be returned to.  To work around this behavior use the noinline function attribute.

     The LEVEL argument must be a constant integer.

     On some machines it may be impossible to determine the return address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function will return 0 or a random value.  In addition, __builtin_frame_address may be used to determine if the top of the stack has been reached.

     This function should only be used with a nonzero argument for debugging purposes.

 -- Built-in Function: void * __builtin_frame_address (unsigned int LEVEL)
     This function is similar to __builtin_return_address, but it returns the address of the function frame rather than the return address of the function.  Calling __builtin_frame_address with a value of 0 yields the frame address of the current function, a value of 1 yields the frame address of the caller of the current function, and so forth.

     The frame is the area on the stack which holds local variables and saved registers.  The frame address is normally the address of the first word pushed on to the stack by the function.  However, the exact definition depends upon the processor and the calling convention.  If the processor has a dedicated frame pointer register, and the function has a frame, then __builtin_frame_address will return the value of the frame pointer register.

     On some machines it may be impossible to determine the frame address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function will return 0 if the first frame pointer is properly initialized by the startup code.

     This function should only be used with a nonzero argument for debugging purposes.

Using vector instructions through built-in functions
====================================================

On some targets, the instruction set contains SIMD vector instructions that operate on multiple values contained in one large register at the same time. For example, on the i386 the MMX, 3Dnow! and SSE extensions can be used this way.

The first step in using these extensions is to provide the necessary data types.  This should be done using an appropriate typedef:

     typedef int v4si __attribute__ ((vector_size (16)));

The int type specifies the base type, while the attribute specifies the vector size for the variable, measured in bytes.  For example, the declaration above causes the compiler to set the mode for the v4si type to be 16 bytes wide and divided into int sized units.  For a 32-bit int this means a vector of 4 units of 4 bytes, and the corresponding mode of foo will be V4SI.

The vector_size attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.

All the basic integer types can be used as base types, both as signed and as unsigned: char, short, int, long, long long.  In addition, float and double can be used to build floating-point vector types.

Specifying a combination that is not valid for the current architecture will cause GCC to synthesize the instructions using a narrower mode. For example, if you specify a variable of type V4SI and your architecture does not allow for this specific SIMD type, GCC will produce code that uses 4 SIs.

The types defined in this manner can be used with a subset of normal C operations.  Currently, GCC will allow using the following operators on these types: +, -, *, /, unary minus, ^, |, &, ~.

The operations behave like C++ valarrays.  Addition is defined as the addition of the corresponding elements of the operands.  For example, in the code below, each of the 4 elements in A will be added to the corresponding 4 elements in B and the resulting vector will be stored in C.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a, b, c;

     c = a + b;

Subtraction, multiplication, division, and the logical operations operate in a similar manner.  Likewise, the result of using the unary minus or complement operators on a vector type is a vector whose elements are the negative or complemented values of the corresponding elements in the operand.

You can declare variables and use them in function calls and returns, as well as in assignments and some casts.  You can specify a vector type as a return type for a function.  Vector types can also be used as function arguments.  It is possible to cast from one vector type to another, provided they are of the same size (in fact, you can also cast vectors to and from other datatypes of the same size).

You cannot operate between vectors of different lengths or different signedness without a cast.

A port that supports hardware vector operations, usually provides a set of built-in functions that can be used to operate on vectors.  For example, a function to add two vectors and multiply the result by a third could look like this:

     v4si f (v4si a, v4si b, v4si c)
     {
       v4si tmp = __builtin_addv4si (a, b);
       return __builtin_mulv4si (tmp, c);
     }

Offsetof
========

GCC implements for both C and C++ a syntactic extension to implement the offsetof macro.

     primary:
     	"__builtin_offsetof" "(" typename "," offsetof_member_designator ")"

     offsetof_member_designator:
     	  identifier
     	| offsetof_member_designator "." identifier
     	| offsetof_member_designator "[" expr "]"

This extension is sufficient such that

     #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)

is a suitable definition of the offsetof macro.  In C++, TYPE may be dependent.  In either case, MEMBER may consist of a single identifier, or a sequence of member accesses and array references.

Built-in functions for atomic memory access
===========================================

The following builtins are intended to be compatible with those described in the Intel Itanium Processor-specific Application Binary Interface, section 7.4.  As such, they depart from the normal GCC practice of using the ``__builtin_'' prefix, and further that they are overloaded such that they work on multiple types.

The definition given in the Intel documentation allows only for the use of the types int, long, long long as well as their unsigned counterparts.  GCC will allow any integral scalar or pointer type that is 1, 2, 4 or 8 bytes in length.

Not all operations are supported by all target processors.  If a particular operation cannot be implemented on the target processor, a warning will be generated and a call an external function will be generated.  The external function will carry the same name as the builtin, with an additional suffix _N where N is the size of the data type.

In most cases, these builtins are considered a full barrier.  That is, no memory operand will be moved across the operation, either forward or backward.  Further, instructions will be issued as necessary to prevent the processor from speculating loads across the operation and from queuing stores after the operation.

All of the routines are are described in the Intel documentation to take ``an optional list of variables protected by the memory barrier''.  It's not clear what is meant by that; it could mean that only the following variables are protected, or it could mean that these variables should in addition be protected.  At present GCC ignores this list and protects all variables which are globally accessible.  If in the future we make some use of this list, an empty list will continue to mean all globally accessible variables.

TYPE __sync_fetch_and_add (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_sub (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_or (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_and (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_xor (TYPE *ptr, TYPE value, ...)
TYPE __sync_fetch_and_nand (TYPE *ptr, TYPE value, ...)
     These builtins perform the operation suggested by the name, and returns the value that had previously been in memory.  That is,

          { tmp = *ptr; *ptr OP= value; return tmp; }
          { tmp = *ptr; *ptr = ~tmp & value; return tmp; }   // nand

TYPE __sync_add_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_sub_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_or_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_and_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_xor_and_fetch (TYPE *ptr, TYPE value, ...)
TYPE __sync_nand_and_fetch (TYPE *ptr, TYPE value, ...)
     These builtins perform the operation suggested by the name, and return the new value.  That is,

          { *ptr OP= value; return *ptr; }
          { *ptr = ~*ptr & value; return *ptr; }   // nand

bool __sync_bool_compare_and_swap (TYPE *ptr, TYPE oldval TYPE newval, ...)
TYPE __sync_val_compare_and_swap (TYPE *ptr, TYPE oldval TYPE newval, ...)
     These builtins perform an atomic compare and swap.  That is, if the current value of *PTR is OLDVAL, then write NEWVAL into *PTR.

     The ``bool'' version returns true if the comparison is successful and NEWVAL was written.  The ``val'' version returns the contents of *PTR before the operation.

__sync_synchronize (...)
     This builtin issues a full memory barrier.

TYPE __sync_lock_test_and_set (TYPE *ptr, TYPE value, ...)
     This builtin, as described by Intel, is not a traditional test-and-set operation, but rather an atomic exchange operation.  It writes VALUE into *PTR, and returns the previous contents of *PTR.

     Many targets have only minimal support for such locks, and do not support a full exchange operation.  In this case, a target may support reduced functionality here by which the only valid value to store is the immediate constant 1.  The exact value actually stored in *PTR is implementation defined.

     This builtin is not a full barrier, but rather an acquire barrier. This means that references after the builtin cannot move to (or be speculated to) before the builtin, but previous memory stores may not be globally visible yet, and previous memory loads may not yet be satisfied.

void __sync_lock_release (TYPE *ptr, ...)
     This builtin releases the lock acquired by __sync_lock_test_and_set. Normally this means writing the constant 0 to *PTR.

     This builtin is not a full barrier, but rather a release barrier. This means that all previous memory stores are globally visible, and all previous memory loads have been satisfied, but following memory reads are not prevented from being speculated to before the barrier.

Object Size Checking Builtins
=============================

GCC implements a limited buffer overflow protection mechanism that can prevent some buffer overflow attacks.

 -- Built-in Function: size_t __builtin_object_size (void * PTR, int TYPE)
     is a built-in construct that returns a constant number of bytes from PTR to the end of the object PTR pointer points to (if known at compile time).  __builtin_object_size never evaluates its arguments for side-effects.  If there are any side-effects in them, it returns (size_t) -1 for TYPE 0 or 1 and (size_t) 0 for TYPE 2 or 3.  If there are multiple objects PTR can point to and all of them are known at compile time, the returned number is the maximum of remaining byte counts in those objects if TYPE & 2 is 0 and minimum if nonzero.  If it is not possible to determine which objects PTR points to at compile time, __builtin_object_size should return (size_t) -1 for TYPE 0 or 1 and (size_t) 0 for TYPE 2 or 3.

     TYPE is an integer constant from 0 to 3.  If the least significant bit is clear, objects are whole variables, if it is set, a closest surrounding subobject is considered the object a pointer points to. The second bit determines if maximum or minimum of remaining bytes is computed.

          struct V { char buf1[10]; int b; char buf2[10]; } var;
          char *p = &var.buf1[1], *q = &var.b;

          /* Here the object p points to is var.  */
          assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
          /* The subobject p points to is var.buf1.  */
          assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
          /* The object q points to is var.  */
          assert (__builtin_object_size (q, 0)
          	== (char *) (&var + 1) - (char *) &var.b);
          /* The subobject q points to is var.b.  */
          assert (__builtin_object_size (q, 1) == sizeof (var.b));

There are built-in functions added for many common string operation functions, e.g. for memcpy __builtin___memcpy_chk built-in is provided.  This built-in has an additional last argument, which is the number of bytes remaining in object the DEST argument points to or (size_t) -1 if the size is not known.

The built-in functions are optimized into the normal string functions like memcpy if the last argument is (size_t) -1 or if it is known at compile time that the destination object will not be overflown.  If the compiler can determine at compile time the object will be always overflown, it issues a warning.

The intended use can be e.g.

     #undef memcpy
     #define bos0(dest) __builtin_object_size (dest, 0)
     #define memcpy(dest, src, n) \
       __builtin___memcpy_chk (dest, src, n, bos0 (dest))

     char *volatile p;
     char buf[10];
     /* It is unknown what object p points to, so this is optimized
        into plain memcpy - no checking is possible.  */
     memcpy (p, "abcde", n);
     /* Destination is known and length too.  It is known at compile
        time there will be no overflow.  */
     memcpy (&buf[5], "abcde", 5);
     /* Destination is known, but the length is not known at compile time.
        This will result in __memcpy_chk call that can check for overflow
        at runtime.  */
     memcpy (&buf[5], "abcde", n);
     /* Destination is known and it is known at compile time there will
        be overflow.  There will be a warning and __memcpy_chk call that
        will abort the program at runtime.  */
     memcpy (&buf[6], "abcde", 5);

Such built-in functions are provided for memcpy, mempcpy, memmove, memset, strcpy, stpcpy, strncpy, strcat and strncat.

There are also checking built-in functions for formatted output functions.

     int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
     int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
     			      const char *fmt, ...);
     int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
     			      va_list ap);
     int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
     			       const char *fmt, va_list ap);

The added FLAG argument is passed unchanged to __sprintf_chk etc. functions and can contain implementation specific flags on what additional security measures the checking function might take, such as handling %n differently.

The OS argument is the object size S points to, like in the other built-in functions.  There is a small difference in the behavior though, if OS is (size_t) -1, the built-in functions are optimized into the non-checking functions only if FLAG is 0, otherwise the checking function is called with OS argument set to (size_t) -1.

In addition to this, there are checking built-in functions __builtin___printf_chk, __builtin___vprintf_chk, __builtin___fprintf_chk and __builtin___vfprintf_chk. These have just one additional argument, FLAG, right before format string FMT.  If the compiler is able to optimize them to fputc etc. functions, it will, otherwise the checking function should be called and the FLAG argument passed to it.

Other built-in functions provided by GCC
========================================

GCC provides a large number of built-in functions other than the ones mentioned above.  Some of these are for internal use in the processing of exceptions or variable-length argument lists and will not be documented here because they may change from time to time; we do not recommend general use of these functions.

The remaining functions are provided for optimization purposes.

GCC includes built-in versions of many of the functions in the standard C library.  The versions prefixed with __builtin_ will always be treated as having the same meaning as the C library function even if you specify the -fno-builtin option.  (see C Dialect Options) Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function will be emitted.

Outside strict ISO C mode (-ansi, -std=c89 or -std=c99), the functions _exit, alloca, bcmp, bzero, dcgettext, dgettext, dremf, dreml, drem, exp10f, exp10l, exp10, ffsll, ffsl, ffs, fprintf_unlocked, fputs_unlocked, gammaf, gammal, gamma, gettext, index, isascii, j0f, j0l, j0, j1f, j1l, j1, jnf, jnl, jn, mempcpy, pow10f, pow10l, pow10, printf_unlocked, rindex, scalbf, scalbl, scalb, signbit, signbitf, signbitl, significandf, significandl, significand, sincosf, sincosl, sincos, stpcpy, stpncpy, strcasecmp, strdup, strfmon, strncasecmp, strndup, toascii, y0f, y0l, y0, y1f, y1l, y1, ynf, ynl and yn may be handled as built-in functions. All these functions have corresponding versions prefixed with __builtin_, which may be used even in strict C89 mode.

The ISO C99 functions _Exit, acoshf, acoshl, acosh, asinhf, asinhl, asinh, atanhf, atanhl, atanh, cabsf, cabsl, cabs, cacosf, cacoshf, cacoshl, cacosh, cacosl, cacos, cargf, cargl, carg, casinf, casinhf, casinhl, casinh, casinl, casin, catanf, catanhf, catanhl, catanh, catanl, catan, cbrtf, cbrtl, cbrt, ccosf, ccoshf, ccoshl, ccosh, ccosl, ccos, cexpf, cexpl, cexp, cimagf, cimagl, cimag, clogf, clogl, clog, conjf, conjl, conj, copysignf, copysignl, copysign, cpowf, cpowl, cpow, cprojf, cprojl, cproj, crealf, creall, creal, csinf, csinhf, csinhl, csinh, csinl, csin, csqrtf, csqrtl, csqrt, ctanf, ctanhf, ctanhl, ctanh, ctanl, ctan, erfcf, erfcl, erfc, erff, erfl, erf, exp2f, exp2l, exp2, expm1f, expm1l, expm1, fdimf, fdiml, fdim, fmaf, fmal, fmaxf, fmaxl, fmax, fma, fminf, fminl, fmin, hypotf, hypotl, hypot, ilogbf, ilogbl, ilogb, imaxabs, isblank, iswblank, lgammaf, lgammal, lgamma, llabs, llrintf, llrintl, llrint, llroundf, llroundl, llround, log1pf, log1pl, log1p, log2f, log2l, log2, logbf, logbl, logb, lrintf, lrintl, lrint, lroundf, lroundl, lround, nearbyintf, nearbyintl, nearbyint, nextafterf, nextafterl, nextafter, nexttowardf, nexttowardl, nexttoward, remainderf, remainderl, remainder, remquof, remquol, remquo, rintf, rintl, rint, roundf, roundl, round, scalblnf, scalblnl, scalbln, scalbnf, scalbnl, scalbn, snprintf, tgammaf, tgammal, tgamma, truncf, truncl, trunc, vfscanf, vscanf, vsnprintf and vsscanf are handled as built-in functions except in strict ISO C90 mode (-ansi or -std=c89).

There are also built-in versions of the ISO C99 functions acosf, acosl, asinf, asinl, atan2f, atan2l, atanf, atanl, ceilf, ceill, cosf, coshf, coshl, cosl, expf, expl, fabsf, fabsl, floorf, floorl, fmodf, fmodl, frexpf, frexpl, ldexpf, ldexpl, log10f, log10l, logf, logl, modfl, modf, powf, powl, sinf, sinhf, sinhl, sinl, sqrtf, sqrtl, tanf, tanhf, tanhl and tanl that are recognized in any mode since ISO C90 reserves these names for the purpose to which ISO C99 puts them.  All these functions have corresponding versions prefixed with __builtin_.

The ISO C94 functions iswalnum, iswalpha, iswcntrl, iswdigit, iswgraph, iswlower, iswprint, iswpunct, iswspace, iswupper, iswxdigit, towlower and towupper are handled as built-in functions except in strict ISO C90 mode (-ansi or -std=c89).

The ISO C90 functions abort, abs, acos, asin, atan2, atan, calloc, ceil, cosh, cos, exit, exp, fabs, floor, fmod, fprintf, fputs, frexp, fscanf, isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit, tolower, toupper, labs, ldexp, log10, log, malloc, memcmp, memcpy, memset, modf, pow, printf, putchar, puts, scanf, sinh, sin, snprintf, sprintf, sqrt, sscanf, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strpbrk, strrchr, strspn, strstr, tanh, tan, vfprintf, vprintf and vsprintf are all recognized as built-in functions unless -fno-builtin is specified (or -fno-builtin-FUNCTION is specified for an individual function).  All of these functions have corresponding versions prefixed with __builtin_.

GCC provides built-in versions of the ISO C99 floating point comparison macros that avoid raising exceptions for unordered operands.  They have the same names as the standard macros ( isgreater, isgreaterequal, isless, islessequal, islessgreater, and isunordered) , with __builtin_ prefixed.  We intend for a library implementor to be able to simply #define each standard macro to its built-in equivalent.

 -- Built-in Function: int __builtin_types_compatible_p (TYPE1, TYPE2)

     You can use the built-in function __builtin_types_compatible_p to determine whether two types are the same.

     This built-in function returns 1 if the unqualified versions of the types TYPE1 and TYPE2 (which are types, not expressions) are compatible, 0 otherwise.  The result of this built-in function can be used in integer constant expressions.

     This built-in function ignores top level qualifiers (e.g., const, volatile).  For example, int is equivalent to const int.

     The type int[] and int[5] are compatible.  On the other hand, int and char * are not compatible, even if the size of their types, on the particular architecture are the same.  Also, the amount of pointer indirection is taken into account when determining similarity.  Consequently, short * is not similar to short **.  Furthermore, two types that are typedefed are considered compatible if their underlying types are compatible.

     An enum type is not considered to be compatible with another enum type even if both are compatible with the same integer type; this is what the C standard specifies. For example, enum {foo, bar} is not similar to enum {hot, dog}.

     You would typically use this function in code whose execution varies depending on the arguments' types.  For example:

          #define foo(x)                                                  \
            ({                                                           \
              typeof (x) tmp = (x);                                       \
              if (__builtin_types_compatible_p (typeof (x), long double)) \
                tmp = foo_long_double (tmp);                              \
              else if (__builtin_types_compatible_p (typeof (x), double)) \
                tmp = foo_double (tmp);                                   \
              else if (__builtin_types_compatible_p (typeof (x), float))  \
                tmp = foo_float (tmp);                                    \
              else                                                        \
                abort ();                                                 \
              tmp;                                                        \
            })

     Note: This construct is only available for C.

 -- Built-in Function: TYPE __builtin_choose_expr (CONST_EXP, EXP1, EXP2)

     You can use the built-in function __builtin_choose_expr to evaluate code depending on the value of a constant expression.  This built-in function returns EXP1 if CONST_EXP, which is a constant expression that must be able to be determined at compile time, is nonzero.  Otherwise it returns 0.

     This built-in function is analogous to the ? : operator in C, except that the expression returned has its type unaltered by promotion rules.  Also, the built-in function does not evaluate the expression that was not chosen.  For example, if CONST_EXP evaluates to true, EXP2 is not evaluated even if it has side-effects.

     This built-in function can return an lvalue if the chosen argument is an lvalue.

     If EXP1 is returned, the return type is the same as EXP1's type.  Similarly, if EXP2 is returned, its return type is the same as EXP2.

     Example:

          #define foo(x)                                                    \
            __builtin_choose_expr (                                         \
              __builtin_types_compatible_p (typeof (x), double),            \
              foo_double (x),                                               \
              __builtin_choose_expr (                                       \
                __builtin_types_compatible_p (typeof (x), float),           \
                foo_float (x),                                              \
                /* The void expression results in a compile-time error  \
                   when assigning the result to something.  */          \
                (void)0))

     Note: This construct is only available for C.  Furthermore, the unused expression (EXP1 or EXP2 depending on the value of CONST_EXP) may still generate syntax errors.  This may change in future revisions.

 -- Built-in Function: int __builtin_constant_p (EXP)
     You can use the built-in function __builtin_constant_p to determine if a value is known to be constant at compile-time and hence that GCC can perform constant-folding on expressions involving that value.  The argument of the function is the value to test.  The function returns the integer 1 if the argument is known to be a compile-time constant and 0 if it is not known to be a compile-time constant.  A return of 0 does not indicate that the value is not a constant, but merely that GCC cannot prove it is a constant with the specified value of the -O option.

     You would typically use this function in an embedded application where memory was a critical resource.  If you have some complex calculation, you may want it to be folded if it involves constants, but need to call a function if it does not.  For example:

          #define Scale_Value(X)      \
            (__builtin_constant_p (X) \
            ? ((X) * SCALE + OFFSET) : Scale (X))

     You may use this built-in function in either a macro or an inline function.  However, if you use it in an inlined function and pass an argument of the function as the argument to the built-in, GCC will never return 1 when you call the inline function with a string constant or compound literal (see Compound Literals) and will not return 1 when you pass a constant numeric value to the inline function unless you specify the -O option.

     You may also use __builtin_constant_p in initializers for static data.  For instance, you can write

          static const int table[] = {
             __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
             /* ... */
          };

     This is an acceptable initializer even if EXPRESSION is not a constant expression.  GCC must be more conservative about evaluating the built-in in this case, because it has no opportunity to perform optimization.

     Previous versions of GCC did not accept this built-in in data initializers.  The earliest version where it is completely safe is 3.0.1.

 -- Built-in Function: long __builtin_expect (long EXP, long C)
     You may use __builtin_expect to provide the compiler with branch prediction information.  In general, you should prefer to use actual profile feedback for this (-fprofile-arcs), as programmers are notoriously bad at predicting how their programs actually perform.  However, there are applications in which this data is hard to collect.

     The return value is the value of EXP, which should be an integral expression.  The value of C must be a compile-time constant.  The semantics of the built-in are that it is expected that EXP == C.  For example:

          if (__builtin_expect (x, 0))
            foo ();

     would indicate that we do not expect to call foo, since we expect x to be zero.  Since you are limited to integral expressions for EXP, you should use constructions such as

          if (__builtin_expect (ptr != NULL, 1))
            error ();

     when testing pointer or floating-point values.

 -- Built-in Function: void __builtin_prefetch (const void *ADDR, ...)
     This function is used to minimize cache-miss latency by moving data into a cache before it is accessed. You can insert calls to __builtin_prefetch into code for which you know addresses of data in memory that is likely to be accessed soon. If the target supports them, data prefetch instructions will be generated. If the prefetch is done early enough before the access then the data will be in the cache by the time it is accessed.

     The value of ADDR is the address of the memory to prefetch. There are two optional arguments, RW and LOCALITY. The value of RW is a compile-time constant one or zero; one means that the prefetch is preparing for a write to the memory address and zero, the default, means that the prefetch is preparing for a read. The value LOCALITY must be a compile-time constant integer between zero and three.  A value of zero means that the data has no temporal locality, so it need not be left in the cache after the access.  A value of three means that the data has a high degree of temporal locality and should be left in all levels of cache possible.  Values of one and two mean, respectively, a low or moderate degree of temporal locality.  The default is three.

          for (i = 0; i < n; i++)
            {
              a[i] = a[i] + b[i];
              __builtin_prefetch (&a[i+j], 1, 1);
              __builtin_prefetch (&b[i+j], 0, 1);
              /* ... */
            }

     Data prefetch does not generate faults if ADDR is invalid, but the address expression itself must be valid.  For example, a prefetch of p->next will not fault if p->next is not a valid address, but evaluation will fault if p is not a valid address.

     If the target does not support data prefetch, the address expression is evaluated if it includes side effects but no other code is generated and GCC does not issue a warning.

 -- Built-in Function: double __builtin_huge_val (void)
     Returns a positive infinity, if supported by the floating-point format, else DBL_MAX.  This function is suitable for implementing the ISO C macro HUGE_VAL.

 -- Built-in Function: float __builtin_huge_valf (void)
     Similar to __builtin_huge_val, except the return type is float.

 -- Built-in Function: long double __builtin_huge_vall (void)
     Similar to __builtin_huge_val, except the return type is long double.

 -- Built-in Function: double __builtin_inf (void)
     Similar to __builtin_huge_val, except a warning is generated if the target floating-point format does not support infinities.

 -- Built-in Function: _Decimal32 __builtin_infd32 (void)
     Similar to __builtin_inf, except the return type is _Decimal32.

 -- Built-in Function: _Decimal64 __builtin_infd64 (void)
     Similar to __builtin_inf, except the return type is _Decimal64.

 -- Built-in Function: _Decimal128 __builtin_infd128 (void)
     Similar to __builtin_inf, except the return type is _Decimal128.

 -- Built-in Function: float __builtin_inff (void)
     Similar to __builtin_inf, except the return type is float. This function is suitable for implementing the ISO C99 macro INFINITY.

 -- Built-in Function: long double __builtin_infl (void)
     Similar to __builtin_inf, except the return type is long double.

 -- Built-in Function: double __builtin_nan (const char *str)
     This is an implementation of the ISO C99 function nan.

     Since ISO C99 defines this function in terms of strtod, which we do not implement, a description of the parsing is in order.  The string is parsed as by strtol; that is, the base is recognized by leading 0 or 0x prefixes.  The number parsed is placed in the significand such that the least significant bit of the number is at the least significant bit of the significand.  The number is truncated to fit the significand field provided.  The significand is forced to be a quiet NaN.

     This function, if given a string literal all of which would have been consumed by strtol, is evaluated early enough that it is considered a compile-time constant.

 -- Built-in Function: _Decimal32 __builtin_nand32 (const char *str)
     Similar to __builtin_nan, except the return type is _Decimal32.

 -- Built-in Function: _Decimal64 __builtin_nand64 (const char *str)
     Similar to __builtin_nan, except the return type is _Decimal64.

 -- Built-in Function: _Decimal128 __builtin_nand128 (const char *str)
     Similar to __builtin_nan, except the return type is _Decimal128.

 -- Built-in Function: float __builtin_nanf (const char *str)
     Similar to __builtin_nan, except the return type is float.

 -- Built-in Function: long double __builtin_nanl (const char *str)
     Similar to __builtin_nan, except the return type is long double.

 -- Built-in Function: double __builtin_nans (const char *str)
     Similar to __builtin_nan, except the significand is forced to be a signaling NaN.  The nans function is proposed by WG14 N965.

 -- Built-in Function: float __builtin_nansf (const char *str)
     Similar to __builtin_nans, except the return type is float.

 -- Built-in Function: long double __builtin_nansl (const char *str)
     Similar to __builtin_nans, except the return type is long double.

 -- Built-in Function: int __builtin_ffs (unsigned int x)
     Returns one plus the index of the least significant 1-bit of X, or if X is zero, returns zero.

 -- Built-in Function: int __builtin_clz (unsigned int x)
     Returns the number of leading 0-bits in X, starting at the most significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_ctz (unsigned int x)
     Returns the number of trailing 0-bits in X, starting at the least significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_popcount (unsigned int x)
     Returns the number of 1-bits in X.

 -- Built-in Function: int __builtin_parity (unsigned int x)
     Returns the parity of X, i.e. the number of 1-bits in X modulo 2.

 -- Built-in Function: int __builtin_ffsl (unsigned long)
     Similar to __builtin_ffs, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_clzl (unsigned long)
     Similar to __builtin_clz, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_ctzl (unsigned long)
     Similar to __builtin_ctz, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_popcountl (unsigned long)
     Similar to __builtin_popcount, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_parityl (unsigned long)
     Similar to __builtin_parity, except the argument type is unsigned long.

 -- Built-in Function: int __builtin_ffsll (unsigned long long)
     Similar to __builtin_ffs, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_clzll (unsigned long long)
     Similar to __builtin_clz, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_ctzll (unsigned long long)
     Similar to __builtin_ctz, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_popcountll (unsigned long long)
     Similar to __builtin_popcount, except the argument type is unsigned long long.

 -- Built-in Function: int __builtin_parityll (unsigned long long)
     Similar to __builtin_parity, except the argument type is unsigned long long.

 -- Built-in Function: double __builtin_powi (double, int)
     Returns the first argument raised to the power of the second.  Unlike the pow function no guarantees about precision and rounding are made.

 -- Built-in Function: float __builtin_powif (float, int)
     Similar to __builtin_powi, except the argument and return types are float.

 -- Built-in Function: long double __builtin_powil (long double, int)
     Similar to __builtin_powi, except the argument and return types are long double.

Built-in Functions Specific to Particular Target Machines
=========================================================

On some target machines, GCC supports many built-in functions specific to those machines.  Generally these generate calls to specific machine instructions, but allow the compiler to schedule those calls.

Alpha Built-in Functions
------------------------

These built-in functions are available for the Alpha family of processors, depending on the command-line switches used.

The following built-in functions are always available.  They all generate the machine instruction that is part of the name.

     long __builtin_alpha_implver (void)
     long __builtin_alpha_rpcc (void)
     long __builtin_alpha_amask (long)
     long __builtin_alpha_cmpbge (long, long)
     long __builtin_alpha_extbl (long, long)
     long __builtin_alpha_extwl (long, long)
     long __builtin_alpha_extll (long, long)
     long __builtin_alpha_extql (long, long)
     long __builtin_alpha_extwh (long, long)
     long __builtin_alpha_extlh (long, long)
     long __builtin_alpha_extqh (long, long)
     long __builtin_alpha_insbl (long, long)
     long __builtin_alpha_inswl (long, long)
     long __builtin_alpha_insll (long, long)
     long __builtin_alpha_insql (long, long)
     long __builtin_alpha_inswh (long, long)
     long __builtin_alpha_inslh (long, long)
     long __builtin_alpha_insqh (long, long)
     long __builtin_alpha_mskbl (long, long)
     long __builtin_alpha_mskwl (long, long)
     long __builtin_alpha_mskll (long, long)
     long __builtin_alpha_mskql (long, long)
     long __builtin_alpha_mskwh (long, long)
     long __builtin_alpha_msklh (long, long)
     long __builtin_alpha_mskqh (long, long)
     long __builtin_alpha_umulh (long, long)
     long __builtin_alpha_zap (long, long)
     long __builtin_alpha_zapnot (long, long)

The following built-in functions are always with -mmax or -mcpu=CPU where CPU is pca56 or later.  They all generate the machine instruction that is part of the name.

     long __builtin_alpha_pklb (long)
     long __builtin_alpha_pkwb (long)
     long __builtin_alpha_unpkbl (long)
     long __builtin_alpha_unpkbw (long)
     long __builtin_alpha_minub8 (long, long)
     long __builtin_alpha_minsb8 (long, long)
     long __builtin_alpha_minuw4 (long, long)
     long __builtin_alpha_minsw4 (long, long)
     long __builtin_alpha_maxub8 (long, long)
     long __builtin_alpha_maxsb8 (long, long)
     long __builtin_alpha_maxuw4 (long, long)
     long __builtin_alpha_maxsw4 (long, long)
     long __builtin_alpha_perr (long, long)

The following built-in functions are always with -mcix or -mcpu=CPU where CPU is ev67 or later.  They all generate the machine instruction that is part of the name.

     long __builtin_alpha_cttz (long)
     long __builtin_alpha_ctlz (long)
     long __builtin_alpha_ctpop (long)

The following builtins are available on systems that use the OSF/1 PALcode.  Normally they invoke the rduniq and wruniq PAL calls, but when invoked with -mtls-kernel, they invoke rdval and wrval.

     void *__builtin_thread_pointer (void)
     void __builtin_set_thread_pointer (void *)

ARM Built-in Functions
----------------------

These built-in functions are available for the ARM family of processors, when the -mcpu=iwmmxt switch is used:

     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef char v8qi __attribute__ ((vector_size (8)));

     int __builtin_arm_getwcx (int)
     void __builtin_arm_setwcx (int, int)
     int __builtin_arm_textrmsb (v8qi, int)
     int __builtin_arm_textrmsh (v4hi, int)
     int __builtin_arm_textrmsw (v2si, int)
     int __builtin_arm_textrmub (v8qi, int)
     int __builtin_arm_textrmuh (v4hi, int)
     int __builtin_arm_textrmuw (v2si, int)
     v8qi __builtin_arm_tinsrb (v8qi, int)
     v4hi __builtin_arm_tinsrh (v4hi, int)
     v2si __builtin_arm_tinsrw (v2si, int)
     long long __builtin_arm_tmia (long long, int, int)
     long long __builtin_arm_tmiabb (long long, int, int)
     long long __builtin_arm_tmiabt (long long, int, int)
     long long __builtin_arm_tmiaph (long long, int, int)
     long long __builtin_arm_tmiatb (long long, int, int)
     long long __builtin_arm_tmiatt (long long, int, int)
     int __builtin_arm_tmovmskb (v8qi)
     int __builtin_arm_tmovmskh (v4hi)
     int __builtin_arm_tmovmskw (v2si)
     long long __builtin_arm_waccb (v8qi)
     long long __builtin_arm_wacch (v4hi)
     long long __builtin_arm_waccw (v2si)
     v8qi __builtin_arm_waddb (v8qi, v8qi)
     v8qi __builtin_arm_waddbss (v8qi, v8qi)
     v8qi __builtin_arm_waddbus (v8qi, v8qi)
     v4hi __builtin_arm_waddh (v4hi, v4hi)
     v4hi __builtin_arm_waddhss (v4hi, v4hi)
     v4hi __builtin_arm_waddhus (v4hi, v4hi)
     v2si __builtin_arm_waddw (v2si, v2si)
     v2si __builtin_arm_waddwss (v2si, v2si)
     v2si __builtin_arm_waddwus (v2si, v2si)
     v8qi __builtin_arm_walign (v8qi, v8qi, int)
     long long __builtin_arm_wand(long long, long long)
     long long __builtin_arm_wandn (long long, long long)
     v8qi __builtin_arm_wavg2b (v8qi, v8qi)
     v8qi __builtin_arm_wavg2br (v8qi, v8qi)
     v4hi __builtin_arm_wavg2h (v4hi, v4hi)
     v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
     v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
     v2si __builtin_arm_wcmpeqw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtsw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtuw (v2si, v2si)
     long long __builtin_arm_wmacs (long long, v4hi, v4hi)
     long long __builtin_arm_wmacsz (v4hi, v4hi)
     long long __builtin_arm_wmacu (long long, v4hi, v4hi)
     long long __builtin_arm_wmacuz (v4hi, v4hi)
     v4hi __builtin_arm_wmadds (v4hi, v4hi)
     v4hi __builtin_arm_wmaddu (v4hi, v4hi)
     v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
     v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
     v2si __builtin_arm_wmaxsw (v2si, v2si)
     v8qi __builtin_arm_wmaxub (v8qi, v8qi)
     v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
     v2si __builtin_arm_wmaxuw (v2si, v2si)
     v8qi __builtin_arm_wminsb (v8qi, v8qi)
     v4hi __builtin_arm_wminsh (v4hi, v4hi)
     v2si __builtin_arm_wminsw (v2si, v2si)
     v8qi __builtin_arm_wminub (v8qi, v8qi)
     v4hi __builtin_arm_wminuh (v4hi, v4hi)
     v2si __builtin_arm_wminuw (v2si, v2si)
     v4hi __builtin_arm_wmulsm (v4hi, v4hi)
     v4hi __builtin_arm_wmulul (v4hi, v4hi)
     v4hi __builtin_arm_wmulum (v4hi, v4hi)
     long long __builtin_arm_wor (long long, long long)
     v2si __builtin_arm_wpackdss (long long, long long)
     v2si __builtin_arm_wpackdus (long long, long long)
     v8qi __builtin_arm_wpackhss (v4hi, v4hi)
     v8qi __builtin_arm_wpackhus (v4hi, v4hi)
     v4hi __builtin_arm_wpackwss (v2si, v2si)
     v4hi __builtin_arm_wpackwus (v2si, v2si)
     long long __builtin_arm_wrord (long long, long long)
     long long __builtin_arm_wrordi (long long, int)
     v4hi __builtin_arm_wrorh (v4hi, long long)
     v4hi __builtin_arm_wrorhi (v4hi, int)
     v2si __builtin_arm_wrorw (v2si, long long)
     v2si __builtin_arm_wrorwi (v2si, int)
     v2si __builtin_arm_wsadb (v8qi, v8qi)
     v2si __builtin_arm_wsadbz (v8qi, v8qi)
     v2si __builtin_arm_wsadh (v4hi, v4hi)
     v2si __builtin_arm_wsadhz (v4hi, v4hi)
     v4hi __builtin_arm_wshufh (v4hi, int)
     long long __builtin_arm_wslld (long long, long long)
     long long __builtin_arm_wslldi (long long, int)
     v4hi __builtin_arm_wsllh (v4hi, long long)
     v4hi __builtin_arm_wsllhi (v4hi, int)
     v2si __builtin_arm_wsllw (v2si, long long)
     v2si __builtin_arm_wsllwi (v2si, int)
     long long __builtin_arm_wsrad (long long, long long)
     long long __builtin_arm_wsradi (long long, int)
     v4hi __builtin_arm_wsrah (v4hi, long long)
     v4hi __builtin_arm_wsrahi (v4hi, int)
     v2si __builtin_arm_wsraw (v2si, long long)
     v2si __builtin_arm_wsrawi (v2si, int)
     long long __builtin_arm_wsrld (long long, long long)
     long long __builtin_arm_wsrldi (long long, int)
     v4hi __builtin_arm_wsrlh (v4hi, long long)
     v4hi __builtin_arm_wsrlhi (v4hi, int)
     v2si __builtin_arm_wsrlw (v2si, long long)
     v2si __builtin_arm_wsrlwi (v2si, int)
     v8qi __builtin_arm_wsubb (v8qi, v8qi)
     v8qi __builtin_arm_wsubbss (v8qi, v8qi)
     v8qi __builtin_arm_wsubbus (v8qi, v8qi)
     v4hi __builtin_arm_wsubh (v4hi, v4hi)
     v4hi __builtin_arm_wsubhss (v4hi, v4hi)
     v4hi __builtin_arm_wsubhus (v4hi, v4hi)
     v2si __builtin_arm_wsubw (v2si, v2si)
     v2si __builtin_arm_wsubwss (v2si, v2si)
     v2si __builtin_arm_wsubwus (v2si, v2si)
     v4hi __builtin_arm_wunpckehsb (v8qi)
     v2si __builtin_arm_wunpckehsh (v4hi)
     long long __builtin_arm_wunpckehsw (v2si)
     v4hi __builtin_arm_wunpckehub (v8qi)
     v2si __builtin_arm_wunpckehuh (v4hi)
     long long __builtin_arm_wunpckehuw (v2si)
     v4hi __builtin_arm_wunpckelsb (v8qi)
     v2si __builtin_arm_wunpckelsh (v4hi)
     long long __builtin_arm_wunpckelsw (v2si)
     v4hi __builtin_arm_wunpckelub (v8qi)
     v2si __builtin_arm_wunpckeluh (v4hi)
     long long __builtin_arm_wunpckeluw (v2si)
     v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
     v2si __builtin_arm_wunpckihw (v2si, v2si)
     v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
     v2si __builtin_arm_wunpckilw (v2si, v2si)
     long long __builtin_arm_wxor (long long, long long)
     long long __builtin_arm_wzero ()

Blackfin Built-in Functions
---------------------------

Currently, there are two Blackfin-specific built-in functions.  These are used for generating CSYNC and SSYNC machine insns without using inline assembly; by using these built-in functions the compiler can automatically add workarounds for hardware errata involving these instructions.  These functions are named as follows:

     void __builtin_bfin_csync (void)
     void __builtin_bfin_ssync (void)

FR-V Built-in Functions
-----------------------

GCC provides many FR-V-specific built-in functions.  In general, these functions are intended to be compatible with those described by FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu Semiconductor.  The two exceptions are __MDUNPACKH and __MBTOHE, the gcc forms of which pass 128-bit values by pointer rather than by value.

Most of the functions are named after specific FR-V instructions. Such functions are said to be ``directly mapped'' and are summarized here in tabular form.

Argument Types
..............

The arguments to the built-in functions can be divided into three groups: register numbers, compile-time constants and run-time values.  In order to make this classification clear at a glance, the arguments and return values are given the following pseudo types:

Pseudo type   Real C type   Constant?   Description
uh   unsigned short   No   an unsigned halfword
uw1   unsigned int   No   an unsigned word
sw1   int   No   a signed word
uw2   unsigned long long   No
an unsigned doubleword
sw2   long long   No   a signed doubleword
const   int   Yes   an integer constant
acc   int   Yes   an ACC register number
iacc   int   Yes   an IACC register number

These pseudo types are not defined by GCC, they are simply a notational convenience used in this manual.

Arguments of type uh, uw1, sw1, uw2 and sw2 are evaluated at run time.  They correspond to register operands in the underlying FR-V instructions.

const arguments represent immediate operands in the underlying FR-V instructions.  They must be compile-time constants.

acc arguments are evaluated at compile time and specify the number of an accumulator register.  For example, an acc argument of 2 will select the ACC2 register.

iacc arguments are similar to acc arguments but specify the number of an IACC register.  See Other Built-in Functions for more details.

Directly-mapped Integer Functions
.................................

The functions listed below map directly to FR-V I-type instructions.

Function prototype   Example usage   Assembly output
sw1 __ADDSS (sw1, sw1)
C = __ADDSS (A, B)
ADDSS A,B,C
sw1 __SCAN (sw1, sw1)
C = __SCAN (A, B)
SCAN A,B,C
sw1 __SCUTSS (sw1)
B = __SCUTSS (A)
SCUTSS A,B
sw1 __SLASS (sw1, sw1)
C = __SLASS (A, B)
SLASS A,B,C
void __SMASS (sw1, sw1)
__SMASS (A, B)
SMASS A,B
void __SMSSS (sw1, sw1)
__SMSSS (A, B)
SMSSS A,B
void __SMU (sw1, sw1)
__SMU (A, B)
SMU A,B
sw2 __SMUL (sw1, sw1)
C = __SMUL (A, B)
SMUL A,B,C
sw1 __SUBSS (sw1, sw1)
C = __SUBSS (A, B)
SUBSS A,B,C
uw2 __UMUL (uw1, uw1)
C = __UMUL (A, B)
UMUL A,B,C

Directly-mapped Media Functions
...............................

The functions listed below map directly to FR-V M-type instructions.

Function prototype   Example usage   Assembly output
uw1 __MABSHS (sw1)
B = __MABSHS (A)
MABSHS A,B
void __MADDACCS (acc, acc)
__MADDACCS (B, A)
MADDACCS A,B
sw1 __MADDHSS (sw1, sw1)
C = __MADDHSS (A, B)
MADDHSS A,B,C
uw1 __MADDHUS (uw1, uw1)
C = __MADDHUS (A, B)
MADDHUS A,B,C
uw1 __MAND (uw1, uw1)
C = __MAND (A, B)
MAND A,B,C
void __MASACCS (acc, acc)
__MASACCS (B, A)
MASACCS A,B
uw1 __MAVEH (uw1, uw1)
C = __MAVEH (A, B)
MAVEH A,B,C
uw2 __MBTOH (uw1)
B = __MBTOH (A)
MBTOH A,B
void __MBTOHE (uw1 *, uw1)
__MBTOHE (&B, A)
MBTOHE A,B
void __MCLRACC (acc)
__MCLRACC (A)
MCLRACC A
void __MCLRACCA (void)
__MCLRACCA ()
MCLRACCA
uw1 __Mcop1 (uw1, uw1)
C = __Mcop1 (A, B)
Mcop1 A,B,C
uw1 __Mcop2 (uw1, uw1)
C = __Mcop2 (A, B)
Mcop2 A,B,C
uw1 __MCPLHI (uw2, const)
C = __MCPLHI (A, B)
MCPLHI A,#B,C
uw1 __MCPLI (uw2, const)
C = __MCPLI (A, B)
MCPLI A,#B,C
void __MCPXIS (acc, sw1, sw1)
__MCPXIS (C, A, B)
MCPXIS A,B,C
void __MCPXIU (acc, uw1, uw1)
__MCPXIU (C, A, B)
MCPXIU A,B,C
void __MCPXRS (acc, sw1, sw1)
__MCPXRS (C, A, B)
MCPXRS A,B,C
void __MCPXRU (acc, uw1, uw1)
__MCPXRU (C, A, B)
MCPXRU A,B,C
uw1 __MCUT (acc, uw1)
C = __MCUT (A, B)
MCUT A,B,C
uw1 __MCUTSS (acc, sw1)
C = __MCUTSS (A, B)
MCUTSS A,B,C
void __MDADDACCS (acc, acc)
__MDADDACCS (B, A)
MDADDACCS A,B
void __MDASACCS (acc, acc)
__MDASACCS (B, A)
MDASACCS A,B
uw2 __MDCUTSSI (acc, const)
C = __MDCUTSSI (A, B)
MDCUTSSI A,#B,C
uw2 __MDPACKH (uw2, uw2)
C = __MDPACKH (A, B)
MDPACKH A,B,C
uw2 __MDROTLI (uw2, const)
C = __MDROTLI (A, B)
MDROTLI A,#B,C
void __MDSUBACCS (acc, acc)
__MDSUBACCS (B, A)
MDSUBACCS A,B
void __MDUNPACKH (uw1 *, uw2)
__MDUNPACKH (&B, A)
MDUNPACKH A,B
uw2 __MEXPDHD (uw1, const)
C = __MEXPDHD (A, B)
MEXPDHD A,#B,C
uw1 __MEXPDHW (uw1, const)
C = __MEXPDHW (A, B)
MEXPDHW A,#B,C
uw1 __MHDSETH (uw1, const)
C = __MHDSETH (A, B)
MHDSETH A,#B,C
sw1 __MHDSETS (const)
B = __MHDSETS (A)
MHDSETS #A,B
uw1 __MHSETHIH (uw1, const)
B = __MHSETHIH (B, A)
MHSETHIH #A,B
sw1 __MHSETHIS (sw1, const)
B = __MHSETHIS (B, A)
MHSETHIS #A,B
uw1 __MHSETLOH (uw1, const)
B = __MHSETLOH (B, A)
MHSETLOH #A,B
sw1 __MHSETLOS (sw1, const)
B = __MHSETLOS (B, A)
MHSETLOS #A,B
uw1 __MHTOB (uw2)
B = __MHTOB (A)
MHTOB A,B
void __MMACHS (acc, sw1, sw1)
__MMACHS (C, A, B)
MMACHS A,B,C
void __MMACHU (acc, uw1, uw1)
__MMACHU (C, A, B)
MMACHU A,B,C
void __MMRDHS (acc, sw1, sw1)
__MMRDHS (C, A, B)
MMRDHS A,B,C
void __MMRDHU (acc, uw1, uw1)
__MMRDHU (C, A, B)
MMRDHU A,B,C
void __MMULHS (acc, sw1, sw1)
__MMULHS (C, A, B)
MMULHS A,B,C
void __MMULHU (acc, uw1, uw1)
__MMULHU (C, A, B)
MMULHU A,B,C
void __MMULXHS (acc, sw1, sw1)
__MMULXHS (C, A, B)
MMULXHS A,B,C
void __MMULXHU (acc, uw1, uw1)
__MMULXHU (C, A, B)
MMULXHU A,B,C
uw1 __MNOT (uw1)
B = __MNOT (A)
MNOT A,B
uw1 __MOR (uw1, uw1)
C = __MOR (A, B)
MOR A,B,C
uw1 __MPACKH (uh, uh)
C = __MPACKH (A, B)
MPACKH A,B,C
sw2 __MQADDHSS (sw2, sw2)
C = __MQADDHSS (A, B)
MQADDHSS A,B,C
uw2 __MQADDHUS (uw2, uw2)
C = __MQADDHUS (A, B)
MQADDHUS A,B,C
void __MQCPXIS (acc, sw2, sw2)
__MQCPXIS (C, A, B)
MQCPXIS A,B,C
void __MQCPXIU (acc, uw2, uw2)
__MQCPXIU (C, A, B)
MQCPXIU A,B,C
void __MQCPXRS (acc, sw2, sw2)
__MQCPXRS (C, A, B)
MQCPXRS A,B,C
void __MQCPXRU (acc, uw2, uw2)
__MQCPXRU (C, A, B)
MQCPXRU A,B,C
sw2 __MQLCLRHS (sw2, sw2)
C = __MQLCLRHS (A, B)
MQLCLRHS A,B,C
sw2 __MQLMTHS (sw2, sw2)
C = __MQLMTHS (A, B)
MQLMTHS A,B,C
void __MQMACHS (acc, sw2, sw2)
__MQMACHS (C, A, B)
MQMACHS A,B,C
void __MQMACHU (acc, uw2, uw2)
__MQMACHU (C, A, B)
MQMACHU A,B,C
void __MQMACXHS (acc, sw2, sw2)
__MQMACXHS (C, A, B)
MQMACXHS A,B,C
void __MQMULHS (acc, sw2, sw2)
__MQMULHS (C, A, B)
MQMULHS A,B,C
void __MQMULHU (acc, uw2, uw2)
__MQMULHU (C, A, B)
MQMULHU A,B,C
void __MQMULXHS (acc, sw2, sw2)
__MQMULXHS (C, A, B)
MQMULXHS A,B,C
void __MQMULXHU (acc, uw2, uw2)
__MQMULXHU (C, A, B)
MQMULXHU A,B,C
sw2 __MQSATHS (sw2, sw2)
C = __MQSATHS (A, B)
MQSATHS A,B,C
uw2 __MQSLLHI (uw2, int)
C = __MQSLLHI (A, B)
MQSLLHI A,B,C
sw2 __MQSRAHI (sw2, int)
C = __MQSRAHI (A, B)
MQSRAHI A,B,C
sw2 __MQSUBHSS (sw2, sw2)
C = __MQSUBHSS (A, B)
MQSUBHSS A,B,C
uw2 __MQSUBHUS (uw2, uw2)
C = __MQSUBHUS (A, B)
MQSUBHUS A,B,C
void __MQXMACHS (acc, sw2, sw2)
__MQXMACHS (C, A, B)
MQXMACHS A,B,C
void __MQXMACXHS (acc, sw2, sw2)
__MQXMACXHS (C, A, B)
MQXMACXHS A,B,C
uw1 __MRDACC (acc)
B = __MRDACC (A)
MRDACC A,B
uw1 __MRDACCG (acc)
B = __MRDACCG (A)
MRDACCG A,B
uw1 __MROTLI (uw1, const)
C = __MROTLI (A, B)
MROTLI A,#B,C
uw1 __MROTRI (uw1, const)
C = __MROTRI (A, B)
MROTRI A,#B,C
sw1 __MSATHS (sw1, sw1)
C = __MSATHS (A, B)
MSATHS A,B,C
uw1 __MSATHU (uw1, uw1)
C = __MSATHU (A, B)
MSATHU A,B,C
uw1 __MSLLHI (uw1, const)
C = __MSLLHI (A, B)
MSLLHI A,#B,C
sw1 __MSRAHI (sw1, const)
C = __MSRAHI (A, B)
MSRAHI A,#B,C
uw1 __MSRLHI (uw1, const)
C = __MSRLHI (A, B)
MSRLHI A,#B,C
void __MSUBACCS (acc, acc)
__MSUBACCS (B, A)
MSUBACCS A,B
sw1 __MSUBHSS (sw1, sw1)
C = __MSUBHSS (A, B)
MSUBHSS A,B,C
uw1 __MSUBHUS (uw1, uw1)
C = __MSUBHUS (A, B)
MSUBHUS A,B,C
void __MTRAP (void)
__MTRAP ()
MTRAP
uw2 __MUNPACKH (uw1)
B = __MUNPACKH (A)
MUNPACKH A,B
uw1 __MWCUT (uw2, uw1)
C = __MWCUT (A, B)
MWCUT A,B,C
void __MWTACC (acc, uw1)
__MWTACC (B, A)
MWTACC A,B
void __MWTACCG (acc, uw1)
__MWTACCG (B, A)
MWTACCG A,B
uw1 __MXOR (uw1, uw1)
C = __MXOR (A, B)
MXOR A,B,C

Raw read/write Functions
........................

This sections describes built-in functions related to read and write instructions to access memory.  These functions generate membar instructions to flush the I/O load and stores where appropriate, as described in Fujitsu's manual described above.

unsigned char __builtin_read8 (void *DATA)

unsigned short __builtin_read16 (void *DATA)

unsigned long __builtin_read32 (void *DATA)

unsigned long long __builtin_read64 (void *DATA)

void __builtin_write8 (void *DATA, unsigned char DATUM)

void __builtin_write16 (void *DATA, unsigned short DATUM)

void __builtin_write32 (void *DATA, unsigned long DATUM)

void __builtin_write64 (void *DATA, unsigned long long DATUM)

Other Built-in Functions
........................

This section describes built-in functions that are not named after a specific FR-V instruction.

sw2 __IACCreadll (iacc REG)
     Return the full 64-bit value of IACC0.  The REG argument is reserved for future expansion and must be 0.

sw1 __IACCreadl (iacc REG)
     Return the value of IACC0H if REG is 0 and IACC0L if REG is 1. Other values of REG are rejected as invalid.

void __IACCsetll (iacc REG, sw2 X)
     Set the full 64-bit value of IACC0 to X.  The REG argument is reserved for future expansion and must be 0.

void __IACCsetl (iacc REG, sw1 X)
     Set IACC0H to X if REG is 0 and IACC0L to X if REG is 1.  Other values of REG are rejected as invalid.

void __data_prefetch0 (const void *X)
     Use the dcpl instruction to load the contents of address X into the data cache.

void __data_prefetch (const void *X)
     Use the nldub instruction to load the contents of address X into the data cache.  The instruction will be issued in slot I1.

X86 Built-in Functions
----------------------

These built-in functions are available for the i386 and x86-64 family of computers, depending on the command-line switches used.

Note that, if you specify command-line switches such as -msse, the compiler could use the extended instruction sets even if the built-ins are not used explicitly in the program.  For this reason, applications which perform runtime CPU detection must compile separate files for each supported architecture, using the appropriate flags.  In particular, the file containing the CPU detection code should be compiled without these options.

The following machine modes are available for use with MMX built-in functions (see Vector Extensions): V2SI for a vector of two 32-bit integers, V4HI for a vector of four 16-bit integers, and V8QI for a vector of eight 8-bit integers.  Some of the built-in functions operate on MMX registers as a whole 64-bit entity, these use DI as their mode.

If 3Dnow extensions are enabled, V2SF is used as a mode for a vector of two 32-bit floating point values.

If SSE extensions are enabled, V4SF is used for a vector of four 32-bit floating point values.  Some instructions use a vector of four 32-bit integers, these use V4SI.  Finally, some instructions operate on an entire vector register, interpreting it as a 128-bit integer, these use mode TI.

The following built-in functions are made available by -mmmx. All of them generate the machine instruction that is part of the name.

     v8qi __builtin_ia32_paddb (v8qi, v8qi)
     v4hi __builtin_ia32_paddw (v4hi, v4hi)
     v2si __builtin_ia32_paddd (v2si, v2si)
     v8qi __builtin_ia32_psubb (v8qi, v8qi)
     v4hi __builtin_ia32_psubw (v4hi, v4hi)
     v2si __builtin_ia32_psubd (v2si, v2si)
     v8qi __builtin_ia32_paddsb (v8qi, v8qi)
     v4hi __builtin_ia32_paddsw (v4hi, v4hi)
     v8qi __builtin_ia32_psubsb (v8qi, v8qi)
     v4hi __builtin_ia32_psubsw (v4hi, v4hi)
     v8qi __builtin_ia32_paddusb (v8qi, v8qi)
     v4hi __builtin_ia32_paddusw (v4hi, v4hi)
     v8qi __builtin_ia32_psubusb (v8qi, v8qi)
     v4hi __builtin_ia32_psubusw (v4hi, v4hi)
     v4hi __builtin_ia32_pmullw (v4hi, v4hi)
     v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
     di __builtin_ia32_pand (di, di)
     di __builtin_ia32_pandn (di,di)
     di __builtin_ia32_por (di, di)
     di __builtin_ia32_pxor (di, di)
     v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
     v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
     v2si __builtin_ia32_pcmpeqd (v2si, v2si)
     v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
     v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
     v2si __builtin_ia32_pcmpgtd (v2si, v2si)
     v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
     v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
     v2si __builtin_ia32_punpckhdq (v2si, v2si)
     v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
     v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
     v2si __builtin_ia32_punpckldq (v2si, v2si)
     v8qi __builtin_ia32_packsswb (v4hi, v4hi)
     v4hi __builtin_ia32_packssdw (v2si, v2si)
     v8qi __builtin_ia32_packuswb (v4hi, v4hi)

The following built-in functions are made available either with -msse, or with a combination of -m3dnow and -march=athlon.  All of them generate the machine instruction that is part of the name.

     v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
     v8qi __builtin_ia32_pavgb (v8qi, v8qi)
     v4hi __builtin_ia32_pavgw (v4hi, v4hi)
     v4hi __builtin_ia32_psadbw (v8qi, v8qi)
     v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
     v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
     v8qi __builtin_ia32_pminub (v8qi, v8qi)
     v4hi __builtin_ia32_pminsw (v4hi, v4hi)
     int __builtin_ia32_pextrw (v4hi, int)
     v4hi __builtin_ia32_pinsrw (v4hi, int, int)
     int __builtin_ia32_pmovmskb (v8qi)
     void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
     void __builtin_ia32_movntq (di *, di)
     void __builtin_ia32_sfence (void)

The following built-in functions are available when -msse is used. All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comieq (v4sf, v4sf)
     int __builtin_ia32_comineq (v4sf, v4sf)
     int __builtin_ia32_comilt (v4sf, v4sf)
     int __builtin_ia32_comile (v4sf, v4sf)
     int __builtin_ia32_comigt (v4sf, v4sf)
     int __builtin_ia32_comige (v4sf, v4sf)
     int __builtin_ia32_ucomieq (v4sf, v4sf)
     int __builtin_ia32_ucomineq (v4sf, v4sf)
     int __builtin_ia32_ucomilt (v4sf, v4sf)
     int __builtin_ia32_ucomile (v4sf, v4sf)
     int __builtin_ia32_ucomigt (v4sf, v4sf)
     int __builtin_ia32_ucomige (v4sf, v4sf)
     v4sf __builtin_ia32_addps (v4sf, v4sf)
     v4sf __builtin_ia32_subps (v4sf, v4sf)
     v4sf __builtin_ia32_mulps (v4sf, v4sf)
     v4sf __builtin_ia32_divps (v4sf, v4sf)
     v4sf __builtin_ia32_addss (v4sf, v4sf)
     v4sf __builtin_ia32_subss (v4sf, v4sf)
     v4sf __builtin_ia32_mulss (v4sf, v4sf)
     v4sf __builtin_ia32_divss (v4sf, v4sf)
     v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
     v4si __builtin_ia32_cmpltps (v4sf, v4sf)
     v4si __builtin_ia32_cmpleps (v4sf, v4sf)
     v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
     v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
     v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
     v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
     v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
     v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
     v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
     v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
     v4si __builtin_ia32_cmpordps (v4sf, v4sf)
     v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
     v4si __builtin_ia32_cmpltss (v4sf, v4sf)
     v4si __builtin_ia32_cmpless (v4sf, v4sf)
     v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
     v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
     v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
     v4si __builtin_ia32_cmpnless (v4sf, v4sf)
     v4si __builtin_ia32_cmpordss (v4sf, v4sf)
     v4sf __builtin_ia32_maxps (v4sf, v4sf)
     v4sf __builtin_ia32_maxss (v4sf, v4sf)
     v4sf __builtin_ia32_minps (v4sf, v4sf)
     v4sf __builtin_ia32_minss (v4sf, v4sf)
     v4sf __builtin_ia32_andps (v4sf, v4sf)
     v4sf __builtin_ia32_andnps (v4sf, v4sf)
     v4sf __builtin_ia32_orps (v4sf, v4sf)
     v4sf __builtin_ia32_xorps (v4sf, v4sf)
     v4sf __builtin_ia32_movss (v4sf, v4sf)
     v4sf __builtin_ia32_movhlps (v4sf, v4sf)
     v4sf __builtin_ia32_movlhps (v4sf, v4sf)
     v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
     v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
     v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
     v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
     v2si __builtin_ia32_cvtps2pi (v4sf)
     int __builtin_ia32_cvtss2si (v4sf)
     v2si __builtin_ia32_cvttps2pi (v4sf)
     int __builtin_ia32_cvttss2si (v4sf)
     v4sf __builtin_ia32_rcpps (v4sf)
     v4sf __builtin_ia32_rsqrtps (v4sf)
     v4sf __builtin_ia32_sqrtps (v4sf)
     v4sf __builtin_ia32_rcpss (v4sf)
     v4sf __builtin_ia32_rsqrtss (v4sf)
     v4sf __builtin_ia32_sqrtss (v4sf)
     v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
     void __builtin_ia32_movntps (float *, v4sf)
     int __builtin_ia32_movmskps (v4sf)

The following built-in functions are available when -msse is used.

v4sf __builtin_ia32_loadaps (float *)
     Generates the movaps machine instruction as a load from memory.

void __builtin_ia32_storeaps (float *, v4sf)
     Generates the movaps machine instruction as a store to memory.

v4sf __builtin_ia32_loadups (float *)
     Generates the movups machine instruction as a load from memory.

void __builtin_ia32_storeups (float *, v4sf)
     Generates the movups machine instruction as a store to memory.

v4sf __builtin_ia32_loadsss (float *)
     Generates the movss machine instruction as a load from memory.

void __builtin_ia32_storess (float *, v4sf)
     Generates the movss machine instruction as a store to memory.

v4sf __builtin_ia32_loadhps (v4sf, v2si *)
     Generates the movhps machine instruction as a load from memory.

v4sf __builtin_ia32_loadlps (v4sf, v2si *)
     Generates the movlps machine instruction as a load from memory

void __builtin_ia32_storehps (v4sf, v2si *)
     Generates the movhps machine instruction as a store to memory.

void __builtin_ia32_storelps (v4sf, v2si *)
     Generates the movlps machine instruction as a store to memory.

The following built-in functions are available when -msse2 is used. All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comisdeq (v2df, v2df)
     int __builtin_ia32_comisdlt (v2df, v2df)
     int __builtin_ia32_comisdle (v2df, v2df)
     int __builtin_ia32_comisdgt (v2df, v2df)
     int __builtin_ia32_comisdge (v2df, v2df)
     int __builtin_ia32_comisdneq (v2df, v2df)
     int __builtin_ia32_ucomisdeq (v2df, v2df)
     int __builtin_ia32_ucomisdlt (v2df, v2df)
     int __builtin_ia32_ucomisdle (v2df, v2df)
     int __builtin_ia32_ucomisdgt (v2df, v2df)
     int __builtin_ia32_ucomisdge (v2df, v2df)
     int __builtin_ia32_ucomisdneq (v2df, v2df)
     v2df __builtin_ia32_cmpeqpd (v2df, v2df)
     v2df __builtin_ia32_cmpltpd (v2df, v2df)
     v2df __builtin_ia32_cmplepd (v2df, v2df)
     v2df __builtin_ia32_cmpgtpd (v2df, v2df)
     v2df __builtin_ia32_cmpgepd (v2df, v2df)
     v2df __builtin_ia32_cmpunordpd (v2df, v2df)
     v2df __builtin_ia32_cmpneqpd (v2df, v2df)
     v2df __builtin_ia32_cmpnltpd (v2df, v2df)
     v2df __builtin_ia32_cmpnlepd (v2df, v2df)
     v2df __builtin_ia32_cmpngtpd (v2df, v2df)
     v2df __builtin_ia32_cmpngepd (v2df, v2df)
     v2df __builtin_ia32_cmpordpd (v2df, v2df)
     v2df __builtin_ia32_cmpeqsd (v2df, v2df)
     v2df __builtin_ia32_cmpltsd (v2df, v2df)
     v2df __builtin_ia32_cmplesd (v2df, v2df)
     v2df __builtin_ia32_cmpunordsd (v2df, v2df)
     v2df __builtin_ia32_cmpneqsd (v2df, v2df)
     v2df __builtin_ia32_cmpnltsd (v2df, v2df)
     v2df __builtin_ia32_cmpnlesd (v2df, v2df)
     v2df __builtin_ia32_cmpordsd (v2df, v2df)
     v2di __builtin_ia32_paddq (v2di, v2di)
     v2di __builtin_ia32_psubq (v2di, v2di)
     v2df __builtin_ia32_addpd (v2df, v2df)
     v2df __builtin_ia32_subpd (v2df, v2df)
     v2df __builtin_ia32_mulpd (v2df, v2df)
     v2df __builtin_ia32_divpd (v2df, v2df)
     v2df __builtin_ia32_addsd (v2df, v2df)
     v2df __builtin_ia32_subsd (v2df, v2df)
     v2df __builtin_ia32_mulsd (v2df, v2df)
     v2df __builtin_ia32_divsd (v2df, v2df)
     v2df __builtin_ia32_minpd (v2df, v2df)
     v2df __builtin_ia32_maxpd (v2df, v2df)
     v2df __builtin_ia32_minsd (v2df, v2df)
     v2df __builtin_ia32_maxsd (v2df, v2df)
     v2df __builtin_ia32_andpd (v2df, v2df)
     v2df __builtin_ia32_andnpd (v2df, v2df)
     v2df __builtin_ia32_orpd (v2df, v2df)
     v2df __builtin_ia32_xorpd (v2df, v2df)
     v2df __builtin_ia32_movsd (v2df, v2df)
     v2df __builtin_ia32_unpckhpd (v2df, v2df)
     v2df __builtin_ia32_unpcklpd (v2df, v2df)
     v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
     v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
     v4si __builtin_ia32_paddd128 (v4si, v4si)
     v2di __builtin_ia32_paddq128 (v2di, v2di)
     v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
     v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
     v4si __builtin_ia32_psubd128 (v4si, v4si)
     v2di __builtin_ia32_psubq128 (v2di, v2di)
     v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
     v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
     v2di __builtin_ia32_pand128 (v2di, v2di)
     v2di __builtin_ia32_pandn128 (v2di, v2di)
     v2di __builtin_ia32_por128 (v2di, v2di)
     v2di __builtin_ia32_pxor128 (v2di, v2di)
     v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
     v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
     v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
     v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
     v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
     v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
     v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
     v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
     v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
     v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
     v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
     v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
     v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
     v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
     v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
     v4si __builtin_ia32_punpckldq128 (v4si, v4si)
     v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
     v16qi __builtin_ia32_packsswb128 (v16qi, v16qi)
     v8hi __builtin_ia32_packssdw128 (v8hi, v8hi)
     v16qi __builtin_ia32_packuswb128 (v16qi, v16qi)
     v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
     void __builtin_ia32_maskmovdqu (v16qi, v16qi)
     v2df __builtin_ia32_loadupd (double *)
     void __builtin_ia32_storeupd (double *, v2df)
     v2df __builtin_ia32_loadhpd (v2df, double *)
     v2df __builtin_ia32_loadlpd (v2df, double *)
     int __builtin_ia32_movmskpd (v2df)
     int __builtin_ia32_pmovmskb128 (v16qi)
     void __builtin_ia32_movnti (int *, int)
     void __builtin_ia32_movntpd (double *, v2df)
     void __builtin_ia32_movntdq (v2df *, v2df)
     v4si __builtin_ia32_pshufd (v4si, int)
     v8hi __builtin_ia32_pshuflw (v8hi, int)
     v8hi __builtin_ia32_pshufhw (v8hi, int)
     v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
     v2df __builtin_ia32_sqrtpd (v2df)
     v2df __builtin_ia32_sqrtsd (v2df)
     v2df __builtin_ia32_shufpd (v2df, v2df, int)
     v2df __builtin_ia32_cvtdq2pd (v4si)
     v4sf __builtin_ia32_cvtdq2ps (v4si)
     v4si __builtin_ia32_cvtpd2dq (v2df)
     v2si __builtin_ia32_cvtpd2pi (v2df)
     v4sf __builtin_ia32_cvtpd2ps (v2df)
     v4si __builtin_ia32_cvttpd2dq (v2df)
     v2si __builtin_ia32_cvttpd2pi (v2df)
     v2df __builtin_ia32_cvtpi2pd (v2si)
     int __builtin_ia32_cvtsd2si (v2df)
     int __builtin_ia32_cvttsd2si (v2df)
     long long __builtin_ia32_cvtsd2si64 (v2df)
     long long __builtin_ia32_cvttsd2si64 (v2df)
     v4si __builtin_ia32_cvtps2dq (v4sf)
     v2df __builtin_ia32_cvtps2pd (v4sf)
     v4si __builtin_ia32_cvttps2dq (v4sf)
     v2df __builtin_ia32_cvtsi2sd (v2df, int)
     v2df __builtin_ia32_cvtsi642sd (v2df, long long)
     v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
     v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
     void __builtin_ia32_clflush (const void *)
     void __builtin_ia32_lfence (void)
     void __builtin_ia32_mfence (void)
     v16qi __builtin_ia32_loaddqu (const char *)
     void __builtin_ia32_storedqu (char *, v16qi)
     unsigned long long __builtin_ia32_pmuludq (v2si, v2si)
     v2di __builtin_ia32_pmuludq128 (v4si, v4si)
     v8hi __builtin_ia32_psllw128 (v8hi, v2di)
     v4si __builtin_ia32_pslld128 (v4si, v2di)
     v2di __builtin_ia32_psllq128 (v4si, v2di)
     v8hi __builtin_ia32_psrlw128 (v8hi, v2di)
     v4si __builtin_ia32_psrld128 (v4si, v2di)
     v2di __builtin_ia32_psrlq128 (v2di, v2di)
     v8hi __builtin_ia32_psraw128 (v8hi, v2di)
     v4si __builtin_ia32_psrad128 (v4si, v2di)
     v2di __builtin_ia32_pslldqi128 (v2di, int)
     v8hi __builtin_ia32_psllwi128 (v8hi, int)
     v4si __builtin_ia32_pslldi128 (v4si, int)
     v2di __builtin_ia32_psllqi128 (v2di, int)
     v2di __builtin_ia32_psrldqi128 (v2di, int)
     v8hi __builtin_ia32_psrlwi128 (v8hi, int)
     v4si __builtin_ia32_psrldi128 (v4si, int)
     v2di __builtin_ia32_psrlqi128 (v2di, int)
     v8hi __builtin_ia32_psrawi128 (v8hi, int)
     v4si __builtin_ia32_psradi128 (v4si, int)
     v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)

The following built-in functions are available when -msse3 is used. All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_addsubpd (v2df, v2df)
     v4sf __builtin_ia32_addsubps (v4sf, v4sf)
     v2df __builtin_ia32_haddpd (v2df, v2df)
     v4sf __builtin_ia32_haddps (v4sf, v4sf)
     v2df __builtin_ia32_hsubpd (v2df, v2df)
     v4sf __builtin_ia32_hsubps (v4sf, v4sf)
     v16qi __builtin_ia32_lddqu (char const *)
     void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
     v2df __builtin_ia32_movddup (v2df)
     v4sf __builtin_ia32_movshdup (v4sf)
     v4sf __builtin_ia32_movsldup (v4sf)
     void __builtin_ia32_mwait (unsigned int, unsigned int)

The following built-in functions are available when -msse3 is used.

v2df __builtin_ia32_loadddup (double const *)
     Generates the movddup machine instruction as a load from memory.

The following built-in functions are available when -m3dnow is used. All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_femms (void)
     v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
     v2si __builtin_ia32_pf2id (v2sf)
     v2sf __builtin_ia32_pfacc (v2sf, v2sf)
     v2sf __builtin_ia32_pfadd (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
     v2sf __builtin_ia32_pfmax (v2sf, v2sf)
     v2sf __builtin_ia32_pfmin (v2sf, v2sf)
     v2sf __builtin_ia32_pfmul (v2sf, v2sf)
     v2sf __builtin_ia32_pfrcp (v2sf)
     v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
     v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
     v2sf __builtin_ia32_pfrsqrt (v2sf)
     v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf)
     v2sf __builtin_ia32_pfsub (v2sf, v2sf)
     v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
     v2sf __builtin_ia32_pi2fd (v2si)
     v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)

The following built-in functions are available when both -m3dnow and -march=athlon are used.  All of them generate the machine instruction that is part of the name.

     v2si __builtin_ia32_pf2iw (v2sf)
     v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
     v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
     v2sf __builtin_ia32_pi2fw (v2si)
     v2sf __builtin_ia32_pswapdsf (v2sf)
     v2si __builtin_ia32_pswapdsi (v2si)

MIPS DSP Built-in Functions
---------------------------

The MIPS DSP Application-Specific Extension (ASE) includes new instructions that are designed to improve the performance of DSP and media applications.  It provides instructions that operate on packed 8-bit integer data, Q15 fractional data and Q31 fractional data.

GCC supports MIPS DSP operations using both the generic vector extensions (see Vector Extensions) and a collection of MIPS-specific built-in functions.  Both kinds of support are enabled by the -mdsp command-line option.

At present, GCC only provides support for operations on 32-bit vectors.  The vector type associated with 8-bit integer data is usually called v4i8 and the vector type associated with Q15 is usually called v2q15.  They can be defined in C as follows:

     typedef char v4i8 __attribute__ ((vector_size(4)));
     typedef short v2q15 __attribute__ ((vector_size(4)));

v4i8 and v2q15 values are initialized in the same way as aggregates.  For example:

     v4i8 a = {1, 2, 3, 4};
     v4i8 b;
     b = (v4i8) {5, 6, 7, 8};

     v2q15 c = {0x0fcb, 0x3a75};
     v2q15 d;
     d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};

Note: The CPU's endianness determines the order in which values are packed.  On little-endian targets, the first value is the least significant and the last value is the most significant.  The opposite order applies to big-endian targets.  For example, the code above will set the lowest byte of a to 1 on little-endian targets and 4 on big-endian targets.

Note: Q15 and Q31 values must be initialized with their integer representation.  As shown in this example, the integer representation of a Q15 value can be obtained by multiplying the fractional value by 0x1.0p15.  The equivalent for Q31 values is to multiply by 0x1.0p31.

The table below lists the v4i8 and v2q15 operations for which hardware support exists.  a and b are v4i8 values, and c and d are v2q15 values.

C code   MIPS instruction
a + b   addu.qb
c + d   addq.ph
a - b   subu.qb
c - d   subq.ph

It is easier to describe the DSP built-in functions if we first define the following types:

     typedef int q31;
     typedef int i32;
     typedef long long a64;

q31 and i32 are actually the same as int, but we use q31 to indicate a Q31 fractional value and i32 to indicate a 32-bit integer value.  Similarly, a64 is the same as long long, but we use a64 to indicate values that will be placed in one of the four DSP accumulators ($ac0, $ac1, $ac2 or $ac3).

Also, some built-in functions prefer or require immediate numbers as parameters, because the corresponding DSP instructions accept both immediate numbers and register operands, or accept immediate numbers only.  The immediate parameters are listed as follows.

     imm0_7: 0 to 7.
     imm0_15: 0 to 15.
     imm0_31: 0 to 31.
     imm0_63: 0 to 63.
     imm0_255: 0 to 255.
     imm_n32_31: -32 to 31.
     imm_n512_511: -512 to 511.

The following built-in functions map directly to a particular MIPS DSP instruction.  Please refer to the architecture specification for details on what each instruction does.

     v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
     v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
     q31 __builtin_mips_addq_s_w (q31, q31)
     v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
     v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
     v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
     v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
     q31 __builtin_mips_subq_s_w (q31, q31)
     v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
     v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
     i32 __builtin_mips_addsc (i32, i32)
     i32 __builtin_mips_addwc (i32, i32)
     i32 __builtin_mips_modsub (i32, i32)
     i32 __builtin_mips_raddu_w_qb (v4i8)
     v2q15 __builtin_mips_absq_s_ph (v2q15)
     q31 __builtin_mips_absq_s_w (q31)
     v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
     v2q15 __builtin_mips_precrq_ph_w (q31, q31)
     v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
     v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
     q31 __builtin_mips_preceq_w_phl (v2q15)
     q31 __builtin_mips_preceq_w_phr (v2q15)
     v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
     v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
     v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
     v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
     v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
     v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
     v4i8 __builtin_mips_shll_qb (v4i8, i32)
     v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shll_ph (v2q15, i32)
     v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
     q31 __builtin_mips_shll_s_w (q31, imm0_31)
     q31 __builtin_mips_shll_s_w (q31, i32)
     v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
     v4i8 __builtin_mips_shrl_qb (v4i8, i32)
     v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shra_ph (v2q15, i32)
     v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
     v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
     q31 __builtin_mips_shra_r_w (q31, imm0_31)
     q31 __builtin_mips_shra_r_w (q31, i32)
     v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
     v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
     v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
     q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
     q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
     a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
     a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
     a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
     a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
     a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
     a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
     a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
     a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
     a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
     a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
     i32 __builtin_mips_bitrev (i32)
     i32 __builtin_mips_insv (i32, i32)
     v4i8 __builtin_mips_repl_qb (imm0_255)
     v4i8 __builtin_mips_repl_qb (i32)
     v2q15 __builtin_mips_repl_ph (imm_n512_511)
     v2q15 __builtin_mips_repl_ph (i32)
     void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
     void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
     void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
     i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
     i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
     i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
     void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
     void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
     void __builtin_mips_cmp_le_ph (v2q15, v2q15)
     v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
     v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
     v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
     i32 __builtin_mips_extr_w (a64, imm0_31)
     i32 __builtin_mips_extr_w (a64, i32)
     i32 __builtin_mips_extr_r_w (a64, imm0_31)
     i32 __builtin_mips_extr_s_h (a64, i32)
     i32 __builtin_mips_extr_rs_w (a64, imm0_31)
     i32 __builtin_mips_extr_rs_w (a64, i32)
     i32 __builtin_mips_extr_s_h (a64, imm0_31)
     i32 __builtin_mips_extr_r_w (a64, i32)
     i32 __builtin_mips_extp (a64, imm0_31)
     i32 __builtin_mips_extp (a64, i32)
     i32 __builtin_mips_extpdp (a64, imm0_31)
     i32 __builtin_mips_extpdp (a64, i32)
     a64 __builtin_mips_shilo (a64, imm_n32_31)
     a64 __builtin_mips_shilo (a64, i32)
     a64 __builtin_mips_mthlip (a64, i32)
     void __builtin_mips_wrdsp (i32, imm0_63)
     i32 __builtin_mips_rddsp (imm0_63)
     i32 __builtin_mips_lbux (void *, i32)
     i32 __builtin_mips_lhx (void *, i32)
     i32 __builtin_mips_lwx (void *, i32)
     i32 __builtin_mips_bposge32 (void)

MIPS Paired-Single Support
--------------------------

The MIPS64 architecture includes a number of instructions that operate on pairs of single-precision floating-point values. Each pair is packed into a 64-bit floating-point register, with one element being designated the ``upper half'' and the other being designated the ``lower half''.

GCC supports paired-single operations using both the generic vector extensions (see Vector Extensions) and a collection of MIPS-specific built-in functions.  Both kinds of support are enabled by the -mpaired-single command-line option.

The vector type associated with paired-single values is usually called v2sf.  It can be defined in C as follows:

     typedef float v2sf __attribute__ ((vector_size (8)));

v2sf values are initialized in the same way as aggregates. For example:

     v2sf a = {1.5, 9.1};
     v2sf b;
     float e, f;
     b = (v2sf) {e, f};

Note: The CPU's endianness determines which value is stored in the upper half of a register and which value is stored in the lower half. On little-endian targets, the first value is the lower one and the second value is the upper one.  The opposite order applies to big-endian targets. For example, the code above will set the lower half of a to 1.5 on little-endian targets and 9.1 on big-endian targets.

Paired-Single Arithmetic
........................

The table below lists the v2sf operations for which hardware support exists.  a, b and c are v2sf values and x is an integral value.

C code   MIPS instruction
a + b   add.ps
a - b   sub.ps
-a   neg.ps
a * b   mul.ps
a * b + c   madd.ps
a * b - c   msub.ps
-(a * b + c)   nmadd.ps
-(a * b - c)   nmsub.ps
x ? a : b   movn.ps/movz.ps

Note that the multiply-accumulate instructions can be disabled using the command-line option -mno-fused-madd.

Paired-Single Built-in Functions
................................

The following paired-single functions map directly to a particular MIPS instruction.  Please refer to the architecture specification for details on what each instruction does.

v2sf __builtin_mips_pll_ps (v2sf, v2sf)
     Pair lower lower (pll.ps).

v2sf __builtin_mips_pul_ps (v2sf, v2sf)
     Pair upper lower (pul.ps).

v2sf __builtin_mips_plu_ps (v2sf, v2sf)
     Pair lower upper (plu.ps).

v2sf __builtin_mips_puu_ps (v2sf, v2sf)
     Pair upper upper (puu.ps).

v2sf __builtin_mips_cvt_ps_s (float, float)
     Convert pair to paired single (cvt.ps.s).

float __builtin_mips_cvt_s_pl (v2sf)
     Convert pair lower to single (cvt.s.pl).

float __builtin_mips_cvt_s_pu (v2sf)
     Convert pair upper to single (cvt.s.pu).

v2sf __builtin_mips_abs_ps (v2sf)
     Absolute value (abs.ps).

v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)
     Align variable (alnv.ps).

     Note: The value of the third parameter must be 0 or 4 modulo 8, otherwise the result will be unpredictable.  Please read the instruction description for details.

The following multi-instruction functions are also available. In each case, COND can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.

v2sf __builtin_mips_movt_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
v2sf __builtin_mips_movf_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
     Conditional move based on floating point comparison (c.COND.ps, movt.ps/movf.ps).

     The movt functions return the value X computed by:

          c.COND.ps CC,A,B
          mov.ps X,C
          movt.ps X,D,CC

     The movf functions are similar but use movf.ps instead of movt.ps.

int __builtin_mips_upper_c_COND_ps (v2sf A, v2sf B)
int __builtin_mips_lower_c_COND_ps (v2sf A, v2sf B)
     Comparison of two paired-single values (c.COND.ps, bc1t/bc1f).

     These functions compare A and B using c.COND.ps and return either the upper or lower half of the result.  For example:

          v2sf a, b;
          if (__builtin_mips_upper_c_eq_ps (a, b))
            upper_halves_are_equal ();
          else
            upper_halves_are_unequal ();

          if (__builtin_mips_lower_c_eq_ps (a, b))
            lower_halves_are_equal ();
          else
            lower_halves_are_unequal ();

MIPS-3D Built-in Functions
..........................

The MIPS-3D Application-Specific Extension (ASE) includes additional paired-single instructions that are designed to improve the performance of 3D graphics operations.  Support for these instructions is controlled by the -mips3d command-line option.

The functions listed below map directly to a particular MIPS-3D instruction.  Please refer to the architecture specification for more details on what each instruction does.

v2sf __builtin_mips_addr_ps (v2sf, v2sf)
     Reduction add (addr.ps).

v2sf __builtin_mips_mulr_ps (v2sf, v2sf)
     Reduction multiply (mulr.ps).

v2sf __builtin_mips_cvt_pw_ps (v2sf)
     Convert paired single to paired word (cvt.pw.ps).

v2sf __builtin_mips_cvt_ps_pw (v2sf)
     Convert paired word to paired single (cvt.ps.pw).

float __builtin_mips_recip1_s (float)
double __builtin_mips_recip1_d (double)
v2sf __builtin_mips_recip1_ps (v2sf)
     Reduced precision reciprocal (sequence step 1) (recip1.FMT).

float __builtin_mips_recip2_s (float, float)
double __builtin_mips_recip2_d (double, double)
v2sf __builtin_mips_recip2_ps (v2sf, v2sf)
     Reduced precision reciprocal (sequence step 2) (recip2.FMT).

float __builtin_mips_rsqrt1_s (float)
double __builtin_mips_rsqrt1_d (double)
v2sf __builtin_mips_rsqrt1_ps (v2sf)
     Reduced precision reciprocal square root (sequence step 1) (rsqrt1.FMT).

float __builtin_mips_rsqrt2_s (float, float)
double __builtin_mips_rsqrt2_d (double, double)
v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)
     Reduced precision reciprocal square root (sequence step 2) (rsqrt2.FMT).

The following multi-instruction functions are also available. In each case, COND can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.

int __builtin_mips_cabs_COND_s (float A, float B)
int __builtin_mips_cabs_COND_d (double A, double B)
     Absolute comparison of two scalar values (cabs.COND.FMT, bc1t/bc1f).

     These functions compare A and B using cabs.COND.s or cabs.COND.d and return the result as a boolean value. For example:

          float a, b;
          if (__builtin_mips_cabs_eq_s (a, b))
            true ();
          else
            false ();

int __builtin_mips_upper_cabs_COND_ps (v2sf A, v2sf B)
int __builtin_mips_lower_cabs_COND_ps (v2sf A, v2sf B)
     Absolute comparison of two paired-single values (cabs.COND.ps, bc1t/bc1f).

     These functions compare A and B using cabs.COND.ps and return either the upper or lower half of the result.  For example:

          v2sf a, b;
          if (__builtin_mips_upper_cabs_eq_ps (a, b))
            upper_halves_are_equal ();
          else
            upper_halves_are_unequal ();

          if (__builtin_mips_lower_cabs_eq_ps (a, b))
            lower_halves_are_equal ();
          else
            lower_halves_are_unequal ();

v2sf __builtin_mips_movt_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
v2sf __builtin_mips_movf_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)
     Conditional move based on absolute comparison (cabs.COND.ps, movt.ps/movf.ps).

     The movt functions return the value X computed by:

          cabs.COND.ps CC,A,B
          mov.ps X,C
          movt.ps X,D,CC

     The movf functions are similar but use movf.ps instead of movt.ps.

int __builtin_mips_any_c_COND_ps (v2sf A, v2sf B)
int __builtin_mips_all_c_COND_ps (v2sf A, v2sf B)
int __builtin_mips_any_cabs_COND_ps (v2sf A, v2sf B)
int __builtin_mips_all_cabs_COND_ps (v2sf A, v2sf B)
     Comparison of two paired-single values (c.COND.ps/cabs.COND.ps, bc1any2t/bc1any2f).

     These functions compare A and B using c.COND.ps or cabs.COND.ps.  The any forms return true if either result is true and the all forms return true if both results are true. For example:

          v2sf a, b;
          if (__builtin_mips_any_c_eq_ps (a, b))
            one_is_true ();
          else
            both_are_false ();

          if (__builtin_mips_all_c_eq_ps (a, b))
            both_are_true ();
          else
            one_is_false ();

int __builtin_mips_any_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
int __builtin_mips_all_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
int __builtin_mips_any_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
int __builtin_mips_all_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)
     Comparison of four paired-single values (c.COND.ps/cabs.COND.ps, bc1any4t/bc1any4f).

     These functions use c.COND.ps or cabs.COND.ps to compare A with B and to compare C with D. The any forms return true if any of the four results are true and the all forms return true if all four results are true. For example:

          v2sf a, b, c, d;
          if (__builtin_mips_any_c_eq_4s (a, b, c, d))
            some_are_true ();
          else
            all_are_false ();

          if (__builtin_mips_all_c_eq_4s (a, b, c, d))
            all_are_true ();
          else
            some_are_false ();

PowerPC AltiVec Built-in Functions
----------------------------------

GCC provides an interface for the PowerPC family of processors to access the AltiVec operations described in Motorola's AltiVec Programming Interface Manual.  The interface is made available by including <altivec.h> and using -maltivec and -mabi=altivec.  The interface supports the following vector types.

     vector unsigned char
     vector signed char
     vector bool char

     vector unsigned short
     vector signed short
     vector bool short
     vector pixel

     vector unsigned int
     vector signed int
     vector bool int
     vector float

GCC's implementation of the high-level language interface available from C and C++ code differs from Motorola's documentation in several ways.

  * A vector constant is a list of constant expressions within curly braces.

  * A vector initializer requires no cast if the vector constant is of the same type as the variable it is initializing.

  * If signed or unsigned is omitted, the signedness of the vector type is the default signedness of the base type.  The default varies depending on the operating system, so a portable program should always specify the signedness.

  * Compiling with -maltivec adds keywords __vector, __pixel, and __bool.  Macros vector, pixel, and bool are defined in <altivec.h> and can be undefined.

  * GCC allows using a typedef name as the type specifier for a vector type.

  * For C, overloaded functions are implemented with macros so the following does not work:

            vec_add ((vector signed int){1, 2, 3, 4}, foo);

     Since vec_add is a macro, the vector constant in the example is treated as four separate arguments.  Wrap the entire argument in parentheses for this to work.

Note: Only the <altivec.h> interface is supported. Internally, GCC uses built-in functions to achieve the functionality in the aforementioned header file, but they are not supported and are subject to change without notice.

The following interfaces are supported for the generic and specific AltiVec operations and the AltiVec predicates.  In cases where there is a direct mapping between generic and specific operations, only the generic names are shown here, although the specific operations can also be used.

Arguments that are documented as const int require literal integral values within the range required for that operation.

     vector signed char vec_abs (vector signed char);
     vector signed short vec_abs (vector signed short);
     vector signed int vec_abs (vector signed int);
     vector float vec_abs (vector float);

     vector signed char vec_abss (vector signed char);
     vector signed short vec_abss (vector signed short);
     vector signed int vec_abss (vector signed int);

     vector signed char vec_add (vector bool char, vector signed char);
     vector signed char vec_add (vector signed char, vector bool char);
     vector signed char vec_add (vector signed char, vector signed char);
     vector unsigned char vec_add (vector bool char, vector unsigned char);
     vector unsigned char vec_add (vector unsigned char, vector bool char);
     vector unsigned char vec_add (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_add (vector bool short, vector signed short);
     vector signed short vec_add (vector signed short, vector bool short);
     vector signed short vec_add (vector signed short, vector signed short);
     vector unsigned short vec_add (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_add (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_add (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_add (vector bool int, vector signed int);
     vector signed int vec_add (vector signed int, vector bool int);
     vector signed int vec_add (vector signed int, vector signed int);
     vector unsigned int vec_add (vector bool int, vector unsigned int);
     vector unsigned int vec_add (vector unsigned int, vector bool int);
     vector unsigned int vec_add (vector unsigned int, vector unsigned int);
     vector float vec_add (vector float, vector float);

     vector float vec_vaddfp (vector float, vector float);

     vector signed int vec_vadduwm (vector bool int, vector signed int);
     vector signed int vec_vadduwm (vector signed int, vector bool int);
     vector signed int vec_vadduwm (vector signed int, vector signed int);
     vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
     vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
     vector unsigned int vec_vadduwm (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vadduhm (vector bool short,
                                      vector signed short);
     vector signed short vec_vadduhm (vector signed short,
                                      vector bool short);
     vector signed short vec_vadduhm (vector signed short,
                                      vector signed short);
     vector unsigned short vec_vadduhm (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vadduhm (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vadduhm (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vaddubm (vector bool char, vector signed char);
     vector signed char vec_vaddubm (vector signed char, vector bool char);
     vector signed char vec_vaddubm (vector signed char, vector signed char);
     vector unsigned char vec_vaddubm (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vaddubm (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vaddubm (vector unsigned char,
                                       vector unsigned char);

     vector unsigned int vec_addc (vector unsigned int, vector unsigned int);

     vector unsigned char vec_adds (vector bool char, vector unsigned char);
     vector unsigned char vec_adds (vector unsigned char, vector bool char);
     vector unsigned char vec_adds (vector unsigned char,
                                    vector unsigned char);
     vector signed char vec_adds (vector bool char, vector signed char);
     vector signed char vec_adds (vector signed char, vector bool char);
     vector signed char vec_adds (vector signed char, vector signed char);
     vector unsigned short vec_adds (vector bool short,
                                     vector unsigned short);
     vector unsigned short vec_adds (vector unsigned short,
                                     vector bool short);
     vector unsigned short vec_adds (vector unsigned short,
                                     vector unsigned short);
     vector signed short vec_adds (vector bool short, vector signed short);
     vector signed short vec_adds (vector signed short, vector bool short);
     vector signed short vec_adds (vector signed short, vector signed short);
     vector unsigned int vec_adds (vector bool int, vector unsigned int);
     vector unsigned int vec_adds (vector unsigned int, vector bool int);
     vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
     vector signed int vec_adds (vector bool int, vector signed int);
     vector signed int vec_adds (vector signed int, vector bool int);
     vector signed int vec_adds (vector signed int, vector signed int);

     vector signed int vec_vaddsws (vector bool int, vector signed int);
     vector signed int vec_vaddsws (vector signed int, vector bool int);
     vector signed int vec_vaddsws (vector signed int, vector signed int);

     vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
     vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
     vector unsigned int vec_vadduws (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vaddshs (vector bool short,
                                      vector signed short);
     vector signed short vec_vaddshs (vector signed short,
                                      vector bool short);
     vector signed short vec_vaddshs (vector signed short,
                                      vector signed short);

     vector unsigned short vec_vadduhs (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vadduhs (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vadduhs (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vaddsbs (vector bool char, vector signed char);
     vector signed char vec_vaddsbs (vector signed char, vector bool char);
     vector signed char vec_vaddsbs (vector signed char, vector signed char);

     vector unsigned char vec_vaddubs (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vaddubs (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vaddubs (vector unsigned char,
                                       vector unsigned char);

     vector float vec_and (vector float, vector float);
     vector float vec_and (vector float, vector bool int);
     vector float vec_and (vector bool int, vector float);
     vector bool int vec_and (vector bool int, vector bool int);
     vector signed int vec_and (vector bool int, vector signed int);
     vector signed int vec_and (vector signed int, vector bool int);
     vector signed int vec_and (vector signed int, vector signed int);
     vector unsigned int vec_and (vector bool int, vector unsigned int);
     vector unsigned int vec_and (vector unsigned int, vector bool int);
     vector unsigned int vec_and (vector unsigned int, vector unsigned int);
     vector bool short vec_and (vector bool short, vector bool short);
     vector signed short vec_and (vector bool short, vector signed short);
     vector signed short vec_and (vector signed short, vector bool short);
     vector signed short vec_and (vector signed short, vector signed short);
     vector unsigned short vec_and (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_and (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_and (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_and (vector bool char, vector signed char);
     vector bool char vec_and (vector bool char, vector bool char);
     vector signed char vec_and (vector signed char, vector bool char);
     vector signed char vec_and (vector signed char, vector signed char);
     vector unsigned char vec_and (vector bool char, vector unsigned char);
     vector unsigned char vec_and (vector unsigned char, vector bool char);
     vector unsigned char vec_and (vector unsigned char,
                                   vector unsigned char);

     vector float vec_andc (vector float, vector float);
     vector float vec_andc (vector float, vector bool int);
     vector float vec_andc (vector bool int, vector float);
     vector bool int vec_andc (vector bool int, vector bool int);
     vector signed int vec_andc (vector bool int, vector signed int);
     vector signed int vec_andc (vector signed int, vector bool int);
     vector signed int vec_andc (vector signed int, vector signed int);
     vector unsigned int vec_andc (vector bool int, vector unsigned int);
     vector unsigned int vec_andc (vector unsigned int, vector bool int);
     vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
     vector bool short vec_andc (vector bool short, vector bool short);
     vector signed short vec_andc (vector bool short, vector signed short);
     vector signed short vec_andc (vector signed short, vector bool short);
     vector signed short vec_andc (vector signed short, vector signed short);
     vector unsigned short vec_andc (vector bool short,
                                     vector unsigned short);
     vector unsigned short vec_andc (vector unsigned short,
                                     vector bool short);
     vector unsigned short vec_andc (vector unsigned short,
                                     vector unsigned short);
     vector signed char vec_andc (vector bool char, vector signed char);
     vector bool char vec_andc (vector bool char, vector bool char);
     vector signed char vec_andc (vector signed char, vector bool char);
     vector signed char vec_andc (vector signed char, vector signed char);
     vector unsigned char vec_andc (vector bool char, vector unsigned char);
     vector unsigned char vec_andc (vector unsigned char, vector bool char);
     vector unsigned char vec_andc (vector unsigned char,
                                    vector unsigned char);

     vector unsigned char vec_avg (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_avg (vector signed char, vector signed char);
     vector unsigned short vec_avg (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_avg (vector signed short, vector signed short);
     vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
     vector signed int vec_avg (vector signed int, vector signed int);

     vector signed int vec_vavgsw (vector signed int, vector signed int);

     vector unsigned int vec_vavguw (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_vavgsh (vector signed short,
                                     vector signed short);

     vector unsigned short vec_vavguh (vector unsigned short,
                                       vector unsigned short);

     vector signed char vec_vavgsb (vector signed char, vector signed char);

     vector unsigned char vec_vavgub (vector unsigned char,
                                      vector unsigned char);

     vector float vec_ceil (vector float);

     vector signed int vec_cmpb (vector float, vector float);

     vector bool char vec_cmpeq (vector signed char, vector signed char);
     vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
     vector bool short vec_cmpeq (vector signed short, vector signed short);
     vector bool short vec_cmpeq (vector unsigned short,
                                  vector unsigned short);
     vector bool int vec_cmpeq (vector signed int, vector signed int);
     vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
     vector bool int vec_cmpeq (vector float, vector float);

     vector bool int vec_vcmpeqfp (vector float, vector float);

     vector bool int vec_vcmpequw (vector signed int, vector signed int);
     vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);

     vector bool short vec_vcmpequh (vector signed short,
                                     vector signed short);
     vector bool short vec_vcmpequh (vector unsigned short,
                                     vector unsigned short);

     vector bool char vec_vcmpequb (vector signed char, vector signed char);
     vector bool char vec_vcmpequb (vector unsigned char,
                                    vector unsigned char);

     vector bool int vec_cmpge (vector float, vector float);

     vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
     vector bool char vec_cmpgt (vector signed char, vector signed char);
     vector bool short vec_cmpgt (vector unsigned short,
                                  vector unsigned short);
     vector bool short vec_cmpgt (vector signed short, vector signed short);
     vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
     vector bool int vec_cmpgt (vector signed int, vector signed int);
     vector bool int vec_cmpgt (vector float, vector float);

     vector bool int vec_vcmpgtfp (vector float, vector float);

     vector bool int vec_vcmpgtsw (vector signed int, vector signed int);

     vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);

     vector bool short vec_vcmpgtsh (vector signed short,
                                     vector signed short);

     vector bool short vec_vcmpgtuh (vector unsigned short,
                                     vector unsigned short);

     vector bool char vec_vcmpgtsb (vector signed char, vector signed char);

     vector bool char vec_vcmpgtub (vector unsigned char,
                                    vector unsigned char);

     vector bool int vec_cmple (vector float, vector float);

     vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
     vector bool char vec_cmplt (vector signed char, vector signed char);
     vector bool short vec_cmplt (vector unsigned short,
                                  vector unsigned short);
     vector bool short vec_cmplt (vector signed short, vector signed short);
     vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
     vector bool int vec_cmplt (vector signed int, vector signed int);
     vector bool int vec_cmplt (vector float, vector float);

     vector float vec_ctf (vector unsigned int, const int);
     vector float vec_ctf (vector signed int, const int);

     vector float vec_vcfsx (vector signed int, const int);

     vector float vec_vcfux (vector unsigned int, const int);

     vector signed int vec_cts (vector float, const int);

     vector unsigned int vec_ctu (vector float, const int);

     void vec_dss (const int);

     void vec_dssall (void);

     void vec_dst (const vector unsigned char *, int, const int);
     void vec_dst (const vector signed char *, int, const int);
     void vec_dst (const vector bool char *, int, const int);
     void vec_dst (const vector unsigned short *, int, const int);
     void vec_dst (const vector signed short *, int, const int);
     void vec_dst (const vector bool short *, int, const int);
     void vec_dst (const vector pixel *, int, const int);
     void vec_dst (const vector unsigned int *, int, const int);
     void vec_dst (const vector signed int *, int, const int);
     void vec_dst (const vector bool int *, int, const int);
     void vec_dst (const vector float *, int, const int);
     void vec_dst (const unsigned char *, int, const int);
     void vec_dst (const signed char *, int, const int);
     void vec_dst (const unsigned short *, int, const int);
     void vec_dst (const short *, int, const int);
     void vec_dst (const unsigned int *, int, const int);
     void vec_dst (const int *, int, const int);
     void vec_dst (const unsigned long *, int, const int);
     void vec_dst (const long *, int, const int);
     void vec_dst (const float *, int, const int);

     void vec_dstst (const vector unsigned char *, int, const int);
     void vec_dstst (const vector signed char *, int, const int);
     void vec_dstst (const vector bool char *, int, const int);
     void vec_dstst (const vector unsigned short *, int, const int);
     void vec_dstst (const vector signed short *, int, const int);
     void vec_dstst (const vector bool short *, int, const int);
     void vec_dstst (const vector pixel *, int, const int);
     void vec_dstst (const vector unsigned int *, int, const int);
     void vec_dstst (const vector signed int *, int, const int);
     void vec_dstst (const vector bool int *, int, const int);
     void vec_dstst (const vector float *, int, const int);
     void vec_dstst (const unsigned char *, int, const int);
     void vec_dstst (const signed char *, int, const int);
     void vec_dstst (const unsigned short *, int, const int);
     void vec_dstst (const short *, int, const int);
     void vec_dstst (const unsigned int *, int, const int);
     void vec_dstst (const int *, int, const int);
     void vec_dstst (const unsigned long *, int, const int);
     void vec_dstst (const long *, int, const int);
     void vec_dstst (const float *, int, const int);

     void vec_dststt (const vector unsigned char *, int, const int);
     void vec_dststt (const vector signed char *, int, const int);
     void vec_dststt (const vector bool char *, int, const int);
     void vec_dststt (const vector unsigned short *, int, const int);
     void vec_dststt (const vector signed short *, int, const int);
     void vec_dststt (const vector bool short *, int, const int);
     void vec_dststt (const vector pixel *, int, const int);
     void vec_dststt (const vector unsigned int *, int, const int);
     void vec_dststt (const vector signed int *, int, const int);
     void vec_dststt (const vector bool int *, int, const int);
     void vec_dststt (const vector float *, int, const int);
     void vec_dststt (const unsigned char *, int, const int);
     void vec_dststt (const signed char *, int, const int);
     void vec_dststt (const unsigned short *, int, const int);
     void vec_dststt (const short *, int, const int);
     void vec_dststt (const unsigned int *, int, const int);
     void vec_dststt (const int *, int, const int);
     void vec_dststt (const unsigned long *, int, const int);
     void vec_dststt (const long *, int, const int);
     void vec_dststt (const float *, int, const int);

     void vec_dstt (const vector unsigned char *, int, const int);
     void vec_dstt (const vector signed char *, int, const int);
     void vec_dstt (const vector bool char *, int, const int);
     void vec_dstt (const vector unsigned short *, int, const int);
     void vec_dstt (const vector signed short *, int, const int);
     void vec_dstt (const vector bool short *, int, const int);
     void vec_dstt (const vector pixel *, int, const int);
     void vec_dstt (const vector unsigned int *, int, const int);
     void vec_dstt (const vector signed int *, int, const int);
     void vec_dstt (const vector bool int *, int, const int);
     void vec_dstt (const vector float *, int, const int);
     void vec_dstt (const unsigned char *, int, const int);
     void vec_dstt (const signed char *, int, const int);
     void vec_dstt (const unsigned short *, int, const int);
     void vec_dstt (const short *, int, const int);
     void vec_dstt (const unsigned int *, int, const int);
     void vec_dstt (const int *, int, const int);
     void vec_dstt (const unsigned long *, int, const int);
     void vec_dstt (const long *, int, const int);
     void vec_dstt (const float *, int, const int);

     vector float vec_expte (vector float);

     vector float vec_floor (vector float);

     vector float vec_ld (int, const vector float *);
     vector float vec_ld (int, const float *);
     vector bool int vec_ld (int, const vector bool int *);
     vector signed int vec_ld (int, const vector signed int *);
     vector signed int vec_ld (int, const int *);
     vector signed int vec_ld (int, const long *);
     vector unsigned int vec_ld (int, const vector unsigned int *);
     vector unsigned int vec_ld (int, const unsigned int *);
     vector unsigned int vec_ld (int, const unsigned long *);
     vector bool short vec_ld (int, const vector bool short *);
     vector pixel vec_ld (int, const vector pixel *);
     vector signed short vec_ld (int, const vector signed short *);
     vector signed short vec_ld (int, const short *);
     vector unsigned short vec_ld (int, const vector unsigned short *);
     vector unsigned short vec_ld (int, const unsigned short *);
     vector bool char vec_ld (int, const vector bool char *);
     vector signed char vec_ld (int, const vector signed char *);
     vector signed char vec_ld (int, const signed char *);
     vector unsigned char vec_ld (int, const vector unsigned char *);
     vector unsigned char vec_ld (int, const unsigned char *);

     vector signed char vec_lde (int, const signed char *);
     vector unsigned char vec_lde (int, const unsigned char *);
     vector signed short vec_lde (int, const short *);
     vector unsigned short vec_lde (int, const unsigned short *);
     vector float vec_lde (int, const float *);
     vector signed int vec_lde (int, const int *);
     vector unsigned int vec_lde (int, const unsigned int *);
     vector signed int vec_lde (int, const long *);
     vector unsigned int vec_lde (int, const unsigned long *);

     vector float vec_lvewx (int, float *);
     vector signed int vec_lvewx (int, int *);
     vector unsigned int vec_lvewx (int, unsigned int *);
     vector signed int vec_lvewx (int, long *);
     vector unsigned int vec_lvewx (int, unsigned long *);

     vector signed short vec_lvehx (int, short *);
     vector unsigned short vec_lvehx (int, unsigned short *);

     vector signed char vec_lvebx (int, char *);
     vector unsigned char vec_lvebx (int, unsigned char *);

     vector float vec_ldl (int, const vector float *);
     vector float vec_ldl (int, const float *);
     vector bool int vec_ldl (int, const vector bool int *);
     vector signed int vec_ldl (int, const vector signed int *);
     vector signed int vec_ldl (int, const int *);
     vector signed int vec_ldl (int, const long *);
     vector unsigned int vec_ldl (int, const vector unsigned int *);
     vector unsigned int vec_ldl (int, const unsigned int *);
     vector unsigned int vec_ldl (int, const unsigned long *);
     vector bool short vec_ldl (int, const vector bool short *);
     vector pixel vec_ldl (int, const vector pixel *);
     vector signed short vec_ldl (int, const vector signed short *);
     vector signed short vec_ldl (int, const short *);
     vector unsigned short vec_ldl (int, const vector unsigned short *);
     vector unsigned short vec_ldl (int, const unsigned short *);
     vector bool char vec_ldl (int, const vector bool char *);
     vector signed char vec_ldl (int, const vector signed char *);
     vector signed char vec_ldl (int, const signed char *);
     vector unsigned char vec_ldl (int, const vector unsigned char *);
     vector unsigned char vec_ldl (int, const unsigned char *);

     vector float vec_loge (vector float);

     vector unsigned char vec_lvsl (int, const volatile unsigned char *);
     vector unsigned char vec_lvsl (int, const volatile signed char *);
     vector unsigned char vec_lvsl (int, const volatile unsigned short *);
     vector unsigned char vec_lvsl (int, const volatile short *);
     vector unsigned char vec_lvsl (int, const volatile unsigned int *);
     vector unsigned char vec_lvsl (int, const volatile int *);
     vector unsigned char vec_lvsl (int, const volatile unsigned long *);
     vector unsigned char vec_lvsl (int, const volatile long *);
     vector unsigned char vec_lvsl (int, const volatile float *);

     vector unsigned char vec_lvsr (int, const volatile unsigned char *);
     vector unsigned char vec_lvsr (int, const volatile signed char *);
     vector unsigned char vec_lvsr (int, const volatile unsigned short *);
     vector unsigned char vec_lvsr (int, const volatile short *);
     vector unsigned char vec_lvsr (int, const volatile unsigned int *);
     vector unsigned char vec_lvsr (int, const volatile int *);
     vector unsigned char vec_lvsr (int, const volatile unsigned long *);
     vector unsigned char vec_lvsr (int, const volatile long *);
     vector unsigned char vec_lvsr (int, const volatile float *);

     vector float vec_madd (vector float, vector float, vector float);

     vector signed short vec_madds (vector signed short,
                                    vector signed short,
                                    vector signed short);

     vector unsigned char vec_max (vector bool char, vector unsigned char);
     vector unsigned char vec_max (vector unsigned char, vector bool char);
     vector unsigned char vec_max (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_max (vector bool char, vector signed char);
     vector signed char vec_max (vector signed char, vector bool char);
     vector signed char vec_max (vector signed char, vector signed char);
     vector unsigned short vec_max (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_max (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_max (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_max (vector bool short, vector signed short);
     vector signed short vec_max (vector signed short, vector bool short);
     vector signed short vec_max (vector signed short, vector signed short);
     vector unsigned int vec_max (vector bool int, vector unsigned int);
     vector unsigned int vec_max (vector unsigned int, vector bool int);
     vector unsigned int vec_max (vector unsigned int, vector unsigned int);
     vector signed int vec_max (vector bool int, vector signed int);
     vector signed int vec_max (vector signed int, vector bool int);
     vector signed int vec_max (vector signed int, vector signed int);
     vector float vec_max (vector float, vector float);

     vector float vec_vmaxfp (vector float, vector float);

     vector signed int vec_vmaxsw (vector bool int, vector signed int);
     vector signed int vec_vmaxsw (vector signed int, vector bool int);
     vector signed int vec_vmaxsw (vector signed int, vector signed int);

     vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
     vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
     vector unsigned int vec_vmaxuw (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_vmaxsh (vector bool short, vector signed short);
     vector signed short vec_vmaxsh (vector signed short, vector bool short);
     vector signed short vec_vmaxsh (vector signed short,
                                     vector signed short);

     vector unsigned short vec_vmaxuh (vector bool short,
                                       vector unsigned short);
     vector unsigned short vec_vmaxuh (vector unsigned short,
                                       vector bool short);
     vector unsigned short vec_vmaxuh (vector unsigned short,
                                       vector unsigned short);

     vector signed char vec_vmaxsb (vector bool char, vector signed char);
     vector signed char vec_vmaxsb (vector signed char, vector bool char);
     vector signed char vec_vmaxsb (vector signed char, vector signed char);

     vector unsigned char vec_vmaxub (vector bool char,
                                      vector unsigned char);
     vector unsigned char vec_vmaxub (vector unsigned char,
                                      vector bool char);
     vector unsigned char vec_vmaxub (vector unsigned char,
                                      vector unsigned char);

     vector bool char vec_mergeh (vector bool char, vector bool char);
     vector signed char vec_mergeh (vector signed char, vector signed char);
     vector unsigned char vec_mergeh (vector unsigned char,
                                      vector unsigned char);
     vector bool short vec_mergeh (vector bool short, vector bool short);
     vector pixel vec_mergeh (vector pixel, vector pixel);
     vector signed short vec_mergeh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_mergeh (vector unsigned short,
                                       vector unsigned short);
     vector float vec_mergeh (vector float, vector float);
     vector bool int vec_mergeh (vector bool int, vector bool int);
     vector signed int vec_mergeh (vector signed int, vector signed int);
     vector unsigned int vec_mergeh (vector unsigned int,
                                     vector unsigned int);

     vector float vec_vmrghw (vector float, vector float);
     vector bool int vec_vmrghw (vector bool int, vector bool int);
     vector signed int vec_vmrghw (vector signed int, vector signed int);
     vector unsigned int vec_vmrghw (vector unsigned int,
                                     vector unsigned int);

     vector bool short vec_vmrghh (vector bool short, vector bool short);
     vector signed short vec_vmrghh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_vmrghh (vector unsigned short,
                                       vector unsigned short);
     vector pixel vec_vmrghh (vector pixel, vector pixel);

     vector bool char vec_vmrghb (vector bool char, vector bool char);
     vector signed char vec_vmrghb (vector signed char, vector signed char);
     vector unsigned char vec_vmrghb (vector unsigned char,
                                      vector unsigned char);

     vector bool char vec_mergel (vector bool char, vector bool char);
     vector signed char vec_mergel (vector signed char, vector signed char);
     vector unsigned char vec_mergel (vector unsigned char,
                                      vector unsigned char);
     vector bool short vec_mergel (vector bool short, vector bool short);
     vector pixel vec_mergel (vector pixel, vector pixel);
     vector signed short vec_mergel (vector signed short,
                                     vector signed short);
     vector unsigned short vec_mergel (vector unsigned short,
                                       vector unsigned short);
     vector float vec_mergel (vector float, vector float);
     vector bool int vec_mergel (vector bool int, vector bool int);
     vector signed int vec_mergel (vector signed int, vector signed int);
     vector unsigned int vec_mergel (vector unsigned int,
                                     vector unsigned int);

     vector float vec_vmrglw (vector float, vector float);
     vector signed int vec_vmrglw (vector signed int, vector signed int);
     vector unsigned int vec_vmrglw (vector unsigned int,
                                     vector unsigned int);
     vector bool int vec_vmrglw (vector bool int, vector bool int);

     vector bool short vec_vmrglh (vector bool short, vector bool short);
     vector signed short vec_vmrglh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_vmrglh (vector unsigned short,
                                       vector unsigned short);
     vector pixel vec_vmrglh (vector pixel, vector pixel);

     vector bool char vec_vmrglb (vector bool char, vector bool char);
     vector signed char vec_vmrglb (vector signed char, vector signed char);
     vector unsigned char vec_vmrglb (vector unsigned char,
                                      vector unsigned char);

     vector unsigned short vec_mfvscr (void);

     vector unsigned char vec_min (vector bool char, vector unsigned char);
     vector unsigned char vec_min (vector unsigned char, vector bool char);
     vector unsigned char vec_min (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_min (vector bool char, vector signed char);
     vector signed char vec_min (vector signed char, vector bool char);
     vector signed char vec_min (vector signed char, vector signed char);
     vector unsigned short vec_min (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_min (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_min (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_min (vector bool short, vector signed short);
     vector signed short vec_min (vector signed short, vector bool short);
     vector signed short vec_min (vector signed short, vector signed short);
     vector unsigned int vec_min (vector bool int, vector unsigned int);
     vector unsigned int vec_min (vector unsigned int, vector bool int);
     vector unsigned int vec_min (vector unsigned int, vector unsigned int);
     vector signed int vec_min (vector bool int, vector signed int);
     vector signed int vec_min (vector signed int, vector bool int);
     vector signed int vec_min (vector signed int, vector signed int);
     vector float vec_min (vector float, vector float);

     vector float vec_vminfp (vector float, vector float);

     vector signed int vec_vminsw (vector bool int, vector signed int);
     vector signed int vec_vminsw (vector signed int, vector bool int);
     vector signed int vec_vminsw (vector signed int, vector signed int);

     vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
     vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
     vector unsigned int vec_vminuw (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_vminsh (vector bool short, vector signed short);
     vector signed short vec_vminsh (vector signed short, vector bool short);
     vector signed short vec_vminsh (vector signed short,
                                     vector signed short);

     vector unsigned short vec_vminuh (vector bool short,
                                       vector unsigned short);
     vector unsigned short vec_vminuh (vector unsigned short,
                                       vector bool short);
     vector unsigned short vec_vminuh (vector unsigned short,
                                       vector unsigned short);

     vector signed char vec_vminsb (vector bool char, vector signed char);
     vector signed char vec_vminsb (vector signed char, vector bool char);
     vector signed char vec_vminsb (vector signed char, vector signed char);

     vector unsigned char vec_vminub (vector bool char,
                                      vector unsigned char);
     vector unsigned char vec_vminub (vector unsigned char,
                                      vector bool char);
     vector unsigned char vec_vminub (vector unsigned char,
                                      vector unsigned char);

     vector signed short vec_mladd (vector signed short,
                                    vector signed short,
                                    vector signed short);
     vector signed short vec_mladd (vector signed short,
                                    vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_mladd (vector unsigned short,
                                    vector signed short,
                                    vector signed short);
     vector unsigned short vec_mladd (vector unsigned short,
                                      vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_mradds (vector signed short,
                                     vector signed short,
                                     vector signed short);

     vector unsigned int vec_msum (vector unsigned char,
                                   vector unsigned char,
                                   vector unsigned int);
     vector signed int vec_msum (vector signed char,
                                 vector unsigned char,
                                 vector signed int);
     vector unsigned int vec_msum (vector unsigned short,
                                   vector unsigned short,
                                   vector unsigned int);
     vector signed int vec_msum (vector signed short,
                                 vector signed short,
                                 vector signed int);

     vector signed int vec_vmsumshm (vector signed short,
                                     vector signed short,
                                     vector signed int);

     vector unsigned int vec_vmsumuhm (vector unsigned short,
                                       vector unsigned short,
                                       vector unsigned int);

     vector signed int vec_vmsummbm (vector signed char,
                                     vector unsigned char,
                                     vector signed int);

     vector unsigned int vec_vmsumubm (vector unsigned char,
                                       vector unsigned char,
                                       vector unsigned int);

     vector unsigned int vec_msums (vector unsigned short,
                                    vector unsigned short,
                                    vector unsigned int);
     vector signed int vec_msums (vector signed short,
                                  vector signed short,
                                  vector signed int);

     vector signed int vec_vmsumshs (vector signed short,
                                     vector signed short,
                                     vector signed int);

     vector unsigned int vec_vmsumuhs (vector unsigned short,
                                       vector unsigned short,
                                       vector unsigned int);

     void vec_mtvscr (vector signed int);
     void vec_mtvscr (vector unsigned int);
     void vec_mtvscr (vector bool int);
     void vec_mtvscr (vector signed short);
     void vec_mtvscr (vector unsigned short);
     void vec_mtvscr (vector bool short);
     void vec_mtvscr (vector pixel);
     void vec_mtvscr (vector signed char);
     void vec_mtvscr (vector unsigned char);
     void vec_mtvscr (vector bool char);

     vector unsigned short vec_mule (vector unsigned char,
                                     vector unsigned char);
     vector signed short vec_mule (vector signed char,
                                   vector signed char);
     vector unsigned int vec_mule (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_mule (vector signed short, vector signed short);

     vector signed int vec_vmulesh (vector signed short,
                                    vector signed short);

     vector unsigned int vec_vmuleuh (vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_vmulesb (vector signed char,
                                      vector signed char);

     vector unsigned short vec_vmuleub (vector unsigned char,
                                       vector unsigned char);

     vector unsigned short vec_mulo (vector unsigned char,
                                     vector unsigned char);
     vector signed short vec_mulo (vector signed char, vector signed char);
     vector unsigned int vec_mulo (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_mulo (vector signed short, vector signed short);

     vector signed int vec_vmulosh (vector signed short,
                                    vector signed short);

     vector unsigned int vec_vmulouh (vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_vmulosb (vector signed char,
                                      vector signed char);

     vector unsigned short vec_vmuloub (vector unsigned char,
                                        vector unsigned char);

     vector float vec_nmsub (vector float, vector float, vector float);

     vector float vec_nor (vector float, vector float);
     vector signed int vec_nor (vector signed int, vector signed int);
     vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
     vector bool int vec_nor (vector bool int, vector bool int);
     vector signed short vec_nor (vector signed short, vector signed short);
     vector unsigned short vec_nor (vector unsigned short,
                                    vector unsigned short);
     vector bool short vec_nor (vector bool short, vector bool short);
     vector signed char vec_nor (vector signed char, vector signed char);
     vector unsigned char vec_nor (vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_nor (vector bool char, vector bool char);

     vector float vec_or (vector float, vector float);
     vector float vec_or (vector float, vector bool int);
     vector float vec_or (vector bool int, vector float);
     vector bool int vec_or (vector bool int, vector bool int);
     vector signed int vec_or (vector bool int, vector signed int);
     vector signed int vec_or (vector signed int, vector bool int);
     vector signed int vec_or (vector signed int, vector signed int);
     vector unsigned int vec_or (vector bool int, vector unsigned int);
     vector unsigned int vec_or (vector unsigned int, vector bool int);
     vector unsigned int vec_or (vector unsigned int, vector unsigned int);
     vector bool short vec_or (vector bool short, vector bool short);
     vector signed short vec_or (vector bool short, vector signed short);
     vector signed short vec_or (vector signed short, vector bool short);
     vector signed short vec_or (vector signed short, vector signed short);
     vector unsigned short vec_or (vector bool short, vector unsigned short);
     vector unsigned short vec_or (vector unsigned short, vector bool short);
     vector unsigned short vec_or (vector unsigned short,
                                   vector unsigned short);
     vector signed char vec_or (vector bool char, vector signed char);
     vector bool char vec_or (vector bool char, vector bool char);
     vector signed char vec_or (vector signed char, vector bool char);
     vector signed char vec_or (vector signed char, vector signed char);
     vector unsigned char vec_or (vector bool char, vector unsigned char);
     vector unsigned char vec_or (vector unsigned char, vector bool char);
     vector unsigned char vec_or (vector unsigned char,
                                  vector unsigned char);

     vector signed char vec_pack (vector signed short, vector signed short);
     vector unsigned char vec_pack (vector unsigned short,
                                    vector unsigned short);
     vector bool char vec_pack (vector bool short, vector bool short);
     vector signed short vec_pack (vector signed int, vector signed int);
     vector unsigned short vec_pack (vector unsigned int,
                                     vector unsigned int);
     vector bool short vec_pack (vector bool int, vector bool int);

     vector bool short vec_vpkuwum (vector bool int, vector bool int);
     vector signed short vec_vpkuwum (vector signed int, vector signed int);
     vector unsigned short vec_vpkuwum (vector unsigned int,
                                        vector unsigned int);

     vector bool char vec_vpkuhum (vector bool short, vector bool short);
     vector signed char vec_vpkuhum (vector signed short,
                                     vector signed short);
     vector unsigned char vec_vpkuhum (vector unsigned short,
                                       vector unsigned short);

     vector pixel vec_packpx (vector unsigned int, vector unsigned int);

     vector unsigned char vec_packs (vector unsigned short,
                                     vector unsigned short);
     vector signed char vec_packs (vector signed short, vector signed short);
     vector unsigned short vec_packs (vector unsigned int,
                                      vector unsigned int);
     vector signed short vec_packs (vector signed int, vector signed int);

     vector signed short vec_vpkswss (vector signed int, vector signed int);

     vector unsigned short vec_vpkuwus (vector unsigned int,
                                        vector unsigned int);

     vector signed char vec_vpkshss (vector signed short,
                                     vector signed short);

     vector unsigned char vec_vpkuhus (vector unsigned short,
                                       vector unsigned short);

     vector unsigned char vec_packsu (vector unsigned short,
                                      vector unsigned short);
     vector unsigned char vec_packsu (vector signed short,
                                      vector signed short);
     vector unsigned short vec_packsu (vector unsigned int,
                                       vector unsigned int);
     vector unsigned short vec_packsu (vector signed int, vector signed int);

     vector unsigned short vec_vpkswus (vector signed int,
                                        vector signed int);

     vector unsigned char vec_vpkshus (vector signed short,
                                       vector signed short);

     vector float vec_perm (vector float,
                            vector float,
                            vector unsigned char);
     vector signed int vec_perm (vector signed int,
                                 vector signed int,
                                 vector unsigned char);
     vector unsigned int vec_perm (vector unsigned int,
                                   vector unsigned int,
                                   vector unsigned char);
     vector bool int vec_perm (vector bool int,
                               vector bool int,
                               vector unsigned char);
     vector signed short vec_perm (vector signed short,
                                   vector signed short,
                                   vector unsigned char);
     vector unsigned short vec_perm (vector unsigned short,
                                     vector unsigned short,
                                     vector unsigned char);
     vector bool short vec_perm (vector bool short,
                                 vector bool short,
                                 vector unsigned char);
     vector pixel vec_perm (vector pixel,
                            vector pixel,
                            vector unsigned char);
     vector signed char vec_perm (vector signed char,
                                  vector signed char,
                                  vector unsigned char);
     vector unsigned char vec_perm (vector unsigned char,
                                    vector unsigned char,
                                    vector unsigned char);
     vector bool char vec_perm (vector bool char,
                                vector bool char,
                                vector unsigned char);

     vector float vec_re (vector float);

     vector signed char vec_rl (vector signed char,
                                vector unsigned char);
     vector unsigned char vec_rl (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_rl (vector signed short, vector unsigned short);
     vector unsigned short vec_rl (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_rl (vector signed int, vector unsigned int);
     vector unsigned int vec_rl (vector unsigned int, vector unsigned int);

     vector signed int vec_vrlw (vector signed int, vector unsigned int);
     vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);

     vector signed short vec_vrlh (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_vrlh (vector unsigned short,
                                     vector unsigned short);

     vector signed char vec_vrlb (vector signed char, vector unsigned char);
     vector unsigned char vec_vrlb (vector unsigned char,
                                    vector unsigned char);

     vector float vec_round (vector float);

     vector float vec_rsqrte (vector float);

     vector float vec_sel (vector float, vector float, vector bool int);
     vector float vec_sel (vector float, vector float, vector unsigned int);
     vector signed int vec_sel (vector signed int,
                                vector signed int,
                                vector bool int);
     vector signed int vec_sel (vector signed int,
                                vector signed int,
                                vector unsigned int);
     vector unsigned int vec_sel (vector unsigned int,
                                  vector unsigned int,
                                  vector bool int);
     vector unsigned int vec_sel (vector unsigned int,
                                  vector unsigned int,
                                  vector unsigned int);
     vector bool int vec_sel (vector bool int,
                              vector bool int,
                              vector bool int);
     vector bool int vec_sel (vector bool int,
                              vector bool int,
                              vector unsigned int);
     vector signed short vec_sel (vector signed short,
                                  vector signed short,
                                  vector bool short);
     vector signed short vec_sel (vector signed short,
                                  vector signed short,
                                  vector unsigned short);
     vector unsigned short vec_sel (vector unsigned short,
                                    vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_sel (vector unsigned short,
                                    vector unsigned short,
                                    vector unsigned short);
     vector bool short vec_sel (vector bool short,
                                vector bool short,
                                vector bool short);
     vector bool short vec_sel (vector bool short,
                                vector bool short,
                                vector unsigned short);
     vector signed char vec_sel (vector signed char,
                                 vector signed char,
                                 vector bool char);
     vector signed char vec_sel (vector signed char,
                                 vector signed char,
                                 vector unsigned char);
     vector unsigned char vec_sel (vector unsigned char,
                                   vector unsigned char,
                                   vector bool char);
     vector unsigned char vec_sel (vector unsigned char,
                                   vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_sel (vector bool char,
                               vector bool char,
                               vector bool char);
     vector bool char vec_sel (vector bool char,
                               vector bool char,
                               vector unsigned char);

     vector signed char vec_sl (vector signed char,
                                vector unsigned char);
     vector unsigned char vec_sl (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_sl (vector signed short, vector unsigned short);
     vector unsigned short vec_sl (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_sl (vector signed int, vector unsigned int);
     vector unsigned int vec_sl (vector unsigned int, vector unsigned int);

     vector signed int vec_vslw (vector signed int, vector unsigned int);
     vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);

     vector signed short vec_vslh (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_vslh (vector unsigned short,
                                     vector unsigned short);

     vector signed char vec_vslb (vector signed char, vector unsigned char);
     vector unsigned char vec_vslb (vector unsigned char,
                                    vector unsigned char);

     vector float vec_sld (vector float, vector float, const int);
     vector signed int vec_sld (vector signed int,
                                vector signed int,
                                const int);
     vector unsigned int vec_sld (vector unsigned int,
                                  vector unsigned int,
                                  const int);
     vector bool int vec_sld (vector bool int,
                              vector bool int,
                              const int);
     vector signed short vec_sld (vector signed short,
                                  vector signed short,
                                  const int);
     vector unsigned short vec_sld (vector unsigned short,
                                    vector unsigned short,
                                    const int);
     vector bool short vec_sld (vector bool short,
                                vector bool short,
                                const int);
     vector pixel vec_sld (vector pixel,
                           vector pixel,
                           const int);
     vector signed char vec_sld (vector signed char,
                                 vector signed char,
                                 const int);
     vector unsigned char vec_sld (vector unsigned char,
                                   vector unsigned char,
                                   const int);
     vector bool char vec_sld (vector bool char,
                               vector bool char,
                               const int);

     vector signed int vec_sll (vector signed int,
                                vector unsigned int);
     vector signed int vec_sll (vector signed int,
                                vector unsigned short);
     vector signed int vec_sll (vector signed int,
                                vector unsigned char);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned int);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned short);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned char);
     vector bool int vec_sll (vector bool int,
                              vector unsigned int);
     vector bool int vec_sll (vector bool int,
                              vector unsigned short);
     vector bool int vec_sll (vector bool int,
                              vector unsigned char);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned int);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned short);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned char);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned int);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned char);
     vector bool short vec_sll (vector bool short, vector unsigned int);
     vector bool short vec_sll (vector bool short, vector unsigned short);
     vector bool short vec_sll (vector bool short, vector unsigned char);
     vector pixel vec_sll (vector pixel, vector unsigned int);
     vector pixel vec_sll (vector pixel, vector unsigned short);
     vector pixel vec_sll (vector pixel, vector unsigned char);
     vector signed char vec_sll (vector signed char, vector unsigned int);
     vector signed char vec_sll (vector signed char, vector unsigned short);
     vector signed char vec_sll (vector signed char, vector unsigned char);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned int);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned short);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_sll (vector bool char, vector unsigned int);
     vector bool char vec_sll (vector bool char, vector unsigned short);
     vector bool char vec_sll (vector bool char, vector unsigned char);

     vector float vec_slo (vector float, vector signed char);
     vector float vec_slo (vector float, vector unsigned char);
     vector signed int vec_slo (vector signed int, vector signed char);
     vector signed int vec_slo (vector signed int, vector unsigned char);
     vector unsigned int vec_slo (vector unsigned int, vector signed char);
     vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
     vector signed short vec_slo (vector signed short, vector signed char);
     vector signed short vec_slo (vector signed short, vector unsigned char);
     vector unsigned short vec_slo (vector unsigned short,
                                    vector signed char);
     vector unsigned short vec_slo (vector unsigned short,
                                    vector unsigned char);
     vector pixel vec_slo (vector pixel, vector signed char);
     vector pixel vec_slo (vector pixel, vector unsigned char);
     vector signed char vec_slo (vector signed char, vector signed char);
     vector signed char vec_slo (vector signed char, vector unsigned char);
     vector unsigned char vec_slo (vector unsigned char, vector signed char);
     vector unsigned char vec_slo (vector unsigned char,
                                   vector unsigned char);

     vector signed char vec_splat (vector signed char, const int);
     vector unsigned char vec_splat (vector unsigned char, const int);
     vector bool char vec_splat (vector bool char, const int);
     vector signed short vec_splat (vector signed short, const int);
     vector unsigned short vec_splat (vector unsigned short, const int);
     vector bool short vec_splat (vector bool short, const int);
     vector pixel vec_splat (vector pixel, const int);
     vector float vec_splat (vector float, const int);
     vector signed int vec_splat (vector signed int, const int);
     vector unsigned int vec_splat (vector unsigned int, const int);
     vector bool int vec_splat (vector bool int, const int);

     vector float vec_vspltw (vector float, const int);
     vector signed int vec_vspltw (vector signed int, const int);
     vector unsigned int vec_vspltw (vector unsigned int, const int);
     vector bool int vec_vspltw (vector bool int, const int);

     vector bool short vec_vsplth (vector bool short, const int);
     vector signed short vec_vsplth (vector signed short, const int);
     vector unsigned short vec_vsplth (vector unsigned short, const int);
     vector pixel vec_vsplth (vector pixel, const int);

     vector signed char vec_vspltb (vector signed char, const int);
     vector unsigned char vec_vspltb (vector unsigned char, const int);
     vector bool char vec_vspltb (vector bool char, const int);

     vector signed char vec_splat_s8 (const int);

     vector signed short vec_splat_s16 (const int);

     vector signed int vec_splat_s32 (const int);

     vector unsigned char vec_splat_u8 (const int);

     vector unsigned short vec_splat_u16 (const int);

     vector unsigned int vec_splat_u32 (const int);

     vector signed char vec_sr (vector signed char, vector unsigned char);
     vector unsigned char vec_sr (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_sr (vector signed short,
                                 vector unsigned short);
     vector unsigned short vec_sr (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_sr (vector signed int, vector unsigned int);
     vector unsigned int vec_sr (vector unsigned int, vector unsigned int);

     vector signed int vec_vsrw (vector signed int, vector unsigned int);
     vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);

     vector signed short vec_vsrh (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_vsrh (vector unsigned short,
                                     vector unsigned short);

     vector signed char vec_vsrb (vector signed char, vector unsigned char);
     vector unsigned char vec_vsrb (vector unsigned char,
                                    vector unsigned char);

     vector signed char vec_sra (vector signed char, vector unsigned char);
     vector unsigned char vec_sra (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_sra (vector signed short,
                                  vector unsigned short);
     vector unsigned short vec_sra (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_sra (vector signed int, vector unsigned int);
     vector unsigned int vec_sra (vector unsigned int, vector unsigned int);

     vector signed int vec_vsraw (vector signed int, vector unsigned int);
     vector unsigned int vec_vsraw (vector unsigned int,
                                    vector unsigned int);

     vector signed short vec_vsrah (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_vsrah (vector unsigned short,
                                      vector unsigned short);

     vector signed char vec_vsrab (vector signed char, vector unsigned char);
     vector unsigned char vec_vsrab (vector unsigned char,
                                     vector unsigned char);

     vector signed int vec_srl (vector signed int, vector unsigned int);
     vector signed int vec_srl (vector signed int, vector unsigned short);
     vector signed int vec_srl (vector signed int, vector unsigned char);
     vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
     vector unsigned int vec_srl (vector unsigned int,
                                  vector unsigned short);
     vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
     vector bool int vec_srl (vector bool int, vector unsigned int);
     vector bool int vec_srl (vector bool int, vector unsigned short);
     vector bool int vec_srl (vector bool int, vector unsigned char);
     vector signed short vec_srl (vector signed short, vector unsigned int);
     vector signed short vec_srl (vector signed short,
                                  vector unsigned short);
     vector signed short vec_srl (vector signed short, vector unsigned char);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned int);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned char);
     vector bool short vec_srl (vector bool short, vector unsigned int);
     vector bool short vec_srl (vector bool short, vector unsigned short);
     vector bool short vec_srl (vector bool short, vector unsigned char);
     vector pixel vec_srl (vector pixel, vector unsigned int);
     vector pixel vec_srl (vector pixel, vector unsigned short);
     vector pixel vec_srl (vector pixel, vector unsigned char);
     vector signed char vec_srl (vector signed char, vector unsigned int);
     vector signed char vec_srl (vector signed char, vector unsigned short);
     vector signed char vec_srl (vector signed char, vector unsigned char);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned int);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned short);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned char);
     vector bool char vec_srl (vector bool char, vector unsigned int);
     vector bool char vec_srl (vector bool char, vector unsigned short);
     vector bool char vec_srl (vector bool char, vector unsigned char);

     vector float vec_sro (vector float, vector signed char);
     vector float vec_sro (vector float, vector unsigned char);
     vector signed int vec_sro (vector signed int, vector signed char);
     vector signed int vec_sro (vector signed int, vector unsigned char);
     vector unsigned int vec_sro (vector unsigned int, vector signed char);
     vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
     vector signed short vec_sro (vector signed short, vector signed char);
     vector signed short vec_sro (vector signed short, vector unsigned char);
     vector unsigned short vec_sro (vector unsigned short,
                                    vector signed char);
     vector unsigned short vec_sro (vector unsigned short,
                                    vector unsigned char);
     vector pixel vec_sro (vector pixel, vector signed char);
     vector pixel vec_sro (vector pixel, vector unsigned char);
     vector signed char vec_sro (vector signed char, vector signed char);
     vector signed char vec_sro (vector signed char, vector unsigned char);
     vector unsigned char vec_sro (vector unsigned char, vector signed char);
     vector unsigned char vec_sro (vector unsigned char,
                                   vector unsigned char);

     void vec_st (vector float, int, vector float *);
     void vec_st (vector float, int, float *);
     void vec_st (vector signed int, int, vector signed int *);
     void vec_st (vector signed int, int, int *);
     void vec_st (vector unsigned int, int, vector unsigned int *);
     void vec_st (vector unsigned int, int, unsigned int *);
     void vec_st (vector bool int, int, vector bool int *);
     void vec_st (vector bool int, int, unsigned int *);
     void vec_st (vector bool int, int, int *);
     void vec_st (vector signed short, int, vector signed short *);
     void vec_st (vector signed short, int, short *);
     void vec_st (vector unsigned short, int, vector unsigned short *);
     void vec_st (vector unsigned short, int, unsigned short *);
     void vec_st (vector bool short, int, vector bool short *);
     void vec_st (vector bool short, int, unsigned short *);
     void vec_st (vector pixel, int, vector pixel *);
     void vec_st (vector pixel, int, unsigned short *);
     void vec_st (vector pixel, int, short *);
     void vec_st (vector bool short, int, short *);
     void vec_st (vector signed char, int, vector signed char *);
     void vec_st (vector signed char, int, signed char *);
     void vec_st (vector unsigned char, int, vector unsigned char *);
     void vec_st (vector unsigned char, int, unsigned char *);
     void vec_st (vector bool char, int, vector bool char *);
     void vec_st (vector bool char, int, unsigned char *);
     void vec_st (vector bool char, int, signed char *);

     void vec_ste (vector signed char, int, signed char *);
     void vec_ste (vector unsigned char, int, unsigned char *);
     void vec_ste (vector bool char, int, signed char *);
     void vec_ste (vector bool char, int, unsigned char *);
     void vec_ste (vector signed short, int, short *);
     void vec_ste (vector unsigned short, int, unsigned short *);
     void vec_ste (vector bool short, int, short *);
     void vec_ste (vector bool short, int, unsigned short *);
     void vec_ste (vector pixel, int, short *);
     void vec_ste (vector pixel, int, unsigned short *);
     void vec_ste (vector float, int, float *);
     void vec_ste (vector signed int, int, int *);
     void vec_ste (vector unsigned int, int, unsigned int *);
     void vec_ste (vector bool int, int, int *);
     void vec_ste (vector bool int, int, unsigned int *);

     void vec_stvewx (vector float, int, float *);
     void vec_stvewx (vector signed int, int, int *);
     void vec_stvewx (vector unsigned int, int, unsigned int *);
     void vec_stvewx (vector bool int, int, int *);
     void vec_stvewx (vector bool int, int, unsigned int *);

     void vec_stvehx (vector signed short, int, short *);
     void vec_stvehx (vector unsigned short, int, unsigned short *);
     void vec_stvehx (vector bool short, int, short *);
     void vec_stvehx (vector bool short, int, unsigned short *);
     void vec_stvehx (vector pixel, int, short *);
     void vec_stvehx (vector pixel, int, unsigned short *);

     void vec_stvebx (vector signed char, int, signed char *);
     void vec_stvebx (vector unsigned char, int, unsigned char *);
     void vec_stvebx (vector bool char, int, signed char *);
     void vec_stvebx (vector bool char, int, unsigned char *);

     void vec_stl (vector float, int, vector float *);
     void vec_stl (vector float, int, float *);
     void vec_stl (vector signed int, int, vector signed int *);
     void vec_stl (vector signed int, int, int *);
     void vec_stl (vector unsigned int, int, vector unsigned int *);
     void vec_stl (vector unsigned int, int, unsigned int *);
     void vec_stl (vector bool int, int, vector bool int *);
     void vec_stl (vector bool int, int, unsigned int *);
     void vec_stl (vector bool int, int, int *);
     void vec_stl (vector signed short, int, vector signed short *);
     void vec_stl (vector signed short, int, short *);
     void vec_stl (vector unsigned short, int, vector unsigned short *);
     void vec_stl (vector unsigned short, int, unsigned short *);
     void vec_stl (vector bool short, int, vector bool short *);
     void vec_stl (vector bool short, int, unsigned short *);
     void vec_stl (vector bool short, int, short *);
     void vec_stl (vector pixel, int, vector pixel *);
     void vec_stl (vector pixel, int, unsigned short *);
     void vec_stl (vector pixel, int, short *);
     void vec_stl (vector signed char, int, vector signed char *);
     void vec_stl (vector signed char, int, signed char *);
     void vec_stl (vector unsigned char, int, vector unsigned char *);
     void vec_stl (vector unsigned char, int, unsigned char *);
     void vec_stl (vector bool char, int, vector bool char *);
     void vec_stl (vector bool char, int, unsigned char *);
     void vec_stl (vector bool char, int, signed char *);

     vector signed char vec_sub (vector bool char, vector signed char);
     vector signed char vec_sub (vector signed char, vector bool char);
     vector signed char vec_sub (vector signed char, vector signed char);
     vector unsigned char vec_sub (vector bool char, vector unsigned char);
     vector unsigned char vec_sub (vector unsigned char, vector bool char);
     vector unsigned char vec_sub (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_sub (vector bool short, vector signed short);
     vector signed short vec_sub (vector signed short, vector bool short);
     vector signed short vec_sub (vector signed short, vector signed short);
     vector unsigned short vec_sub (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_sub (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_sub (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_sub (vector bool int, vector signed int);
     vector signed int vec_sub (vector signed int, vector bool int);
     vector signed int vec_sub (vector signed int, vector signed int);
     vector unsigned int vec_sub (vector bool int, vector unsigned int);
     vector unsigned int vec_sub (vector unsigned int, vector bool int);
     vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
     vector float vec_sub (vector float, vector float);

     vector float vec_vsubfp (vector float, vector float);

     vector signed int vec_vsubuwm (vector bool int, vector signed int);
     vector signed int vec_vsubuwm (vector signed int, vector bool int);
     vector signed int vec_vsubuwm (vector signed int, vector signed int);
     vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
     vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
     vector unsigned int vec_vsubuwm (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vsubuhm (vector bool short,
                                      vector signed short);
     vector signed short vec_vsubuhm (vector signed short,
                                      vector bool short);
     vector signed short vec_vsubuhm (vector signed short,
                                      vector signed short);
     vector unsigned short vec_vsubuhm (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vsubuhm (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vsubuhm (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vsububm (vector bool char, vector signed char);
     vector signed char vec_vsububm (vector signed char, vector bool char);
     vector signed char vec_vsububm (vector signed char, vector signed char);
     vector unsigned char vec_vsububm (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vsububm (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vsububm (vector unsigned char,
                                       vector unsigned char);

     vector unsigned int vec_subc (vector unsigned int, vector unsigned int);

     vector unsigned char vec_subs (vector bool char, vector unsigned char);
     vector unsigned char vec_subs (vector unsigned char, vector bool char);
     vector unsigned char vec_subs (vector unsigned char,
                                    vector unsigned char);
     vector signed char vec_subs (vector bool char, vector signed char);
     vector signed char vec_subs (vector signed char, vector bool char);
     vector signed char vec_subs (vector signed char, vector signed char);
     vector unsigned short vec_subs (vector bool short,
                                     vector unsigned short);
     vector unsigned short vec_subs (vector unsigned short,
                                     vector bool short);
     vector unsigned short vec_subs (vector unsigned short,
                                     vector unsigned short);
     vector signed short vec_subs (vector bool short, vector signed short);
     vector signed short vec_subs (vector signed short, vector bool short);
     vector signed short vec_subs (vector signed short, vector signed short);
     vector unsigned int vec_subs (vector bool int, vector unsigned int);
     vector unsigned int vec_subs (vector unsigned int, vector bool int);
     vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
     vector signed int vec_subs (vector bool int, vector signed int);
     vector signed int vec_subs (vector signed int, vector bool int);
     vector signed int vec_subs (vector signed int, vector signed int);

     vector signed int vec_vsubsws (vector bool int, vector signed int);
     vector signed int vec_vsubsws (vector signed int, vector bool int);
     vector signed int vec_vsubsws (vector signed int, vector signed int);

     vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
     vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
     vector unsigned int vec_vsubuws (vector unsigned int,
                                      vector unsigned int);

     vector signed short vec_vsubshs (vector bool short,
                                      vector signed short);
     vector signed short vec_vsubshs (vector signed short,
                                      vector bool short);
     vector signed short vec_vsubshs (vector signed short,
                                      vector signed short);

     vector unsigned short vec_vsubuhs (vector bool short,
                                        vector unsigned short);
     vector unsigned short vec_vsubuhs (vector unsigned short,
                                        vector bool short);
     vector unsigned short vec_vsubuhs (vector unsigned short,
                                        vector unsigned short);

     vector signed char vec_vsubsbs (vector bool char, vector signed char);
     vector signed char vec_vsubsbs (vector signed char, vector bool char);
     vector signed char vec_vsubsbs (vector signed char, vector signed char);

     vector unsigned char vec_vsububs (vector bool char,
                                       vector unsigned char);
     vector unsigned char vec_vsububs (vector unsigned char,
                                       vector bool char);
     vector unsigned char vec_vsububs (vector unsigned char,
                                       vector unsigned char);

     vector unsigned int vec_sum4s (vector unsigned char,
                                    vector unsigned int);
     vector signed int vec_sum4s (vector signed char, vector signed int);
     vector signed int vec_sum4s (vector signed short, vector signed int);

     vector signed int vec_vsum4shs (vector signed short, vector signed int);

     vector signed int vec_vsum4sbs (vector signed char, vector signed int);

     vector unsigned int vec_vsum4ubs (vector unsigned char,
                                       vector unsigned int);

     vector signed int vec_sum2s (vector signed int, vector signed int);

     vector signed int vec_sums (vector signed int, vector signed int);

     vector float vec_trunc (vector float);

     vector signed short vec_unpackh (vector signed char);
     vector bool short vec_unpackh (vector bool char);
     vector signed int vec_unpackh (vector signed short);
     vector bool int vec_unpackh (vector bool short);
     vector unsigned int vec_unpackh (vector pixel);

     vector bool int vec_vupkhsh (vector bool short);
     vector signed int vec_vupkhsh (vector signed short);

     vector unsigned int vec_vupkhpx (vector pixel);

     vector bool short vec_vupkhsb (vector bool char);
     vector signed short vec_vupkhsb (vector signed char);

     vector signed short vec_unpackl (vector signed char);
     vector bool short vec_unpackl (vector bool char);
     vector unsigned int vec_unpackl (vector pixel);
     vector signed int vec_unpackl (vector signed short);
     vector bool int vec_unpackl (vector bool short);

     vector unsigned int vec_vupklpx (vector pixel);

     vector bool int vec_vupklsh (vector bool short);
     vector signed int vec_vupklsh (vector signed short);

     vector bool short vec_vupklsb (vector bool char);
     vector signed short vec_vupklsb (vector signed char);

     vector float vec_xor (vector float, vector float);
     vector float vec_xor (vector float, vector bool int);
     vector float vec_xor (vector bool int, vector float);
     vector bool int vec_xor (vector bool int, vector bool int);
     vector signed int vec_xor (vector bool int, vector signed int);
     vector signed int vec_xor (vector signed int, vector bool int);
     vector signed int vec_xor (vector signed int, vector signed int);
     vector unsigned int vec_xor (vector bool int, vector unsigned int);
     vector unsigned int vec_xor (vector unsigned int, vector bool int);
     vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
     vector bool short vec_xor (vector bool short, vector bool short);
     vector signed short vec_xor (vector bool short, vector signed short);
     vector signed short vec_xor (vector signed short, vector bool short);
     vector signed short vec_xor (vector signed short, vector signed short);
     vector unsigned short vec_xor (vector bool short,
                                    vector unsigned short);
     vector unsigned short vec_xor (vector unsigned short,
                                    vector bool short);
     vector unsigned short vec_xor (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_xor (vector bool char, vector signed char);
     vector bool char vec_xor (vector bool char, vector bool char);
     vector signed char vec_xor (vector signed char, vector bool char);
     vector signed char vec_xor (vector signed char, vector signed char);
     vector unsigned char vec_xor (vector bool char, vector unsigned char);
     vector unsigned char vec_xor (vector unsigned char, vector bool char);
     vector unsigned char vec_xor (vector unsigned char,
                                   vector unsigned char);

     int vec_all_eq (vector signed char, vector bool char);
     int vec_all_eq (vector signed char, vector signed char);
     int vec_all_eq (vector unsigned char, vector bool char);
     int vec_all_eq (vector unsigned char, vector unsigned char);
     int vec_all_eq (vector bool char, vector bool char);
     int vec_all_eq (vector bool char, vector unsigned char);
     int vec_all_eq (vector bool char, vector signed char);
     int vec_all_eq (vector signed short, vector bool short);
     int vec_all_eq (vector signed short, vector signed short);
     int vec_all_eq (vector unsigned short, vector bool short);
     int vec_all_eq (vector unsigned short, vector unsigned short);
     int vec_all_eq (vector bool short, vector bool short);
     int vec_all_eq (vector bool short, vector unsigned short);
     int vec_all_eq (vector bool short, vector signed short);
     int vec_all_eq (vector pixel, vector pixel);
     int vec_all_eq (vector signed int, vector bool int);
     int vec_all_eq (vector signed int, vector signed int);
     int vec_all_eq (vector unsigned int, vector bool int);
     int vec_all_eq (vector unsigned int, vector unsigned int);
     int vec_all_eq (vector bool int, vector bool int);
     int vec_all_eq (vector bool int, vector unsigned int);
     int vec_all_eq (vector bool int, vector signed int);
     int vec_all_eq (vector float, vector float);

     int vec_all_ge (vector bool char, vector unsigned char);
     int vec_all_ge (vector unsigned char, vector bool char);
     int vec_all_ge (vector unsigned char, vector unsigned char);
     int vec_all_ge (vector bool char, vector signed char);
     int vec_all_ge (vector signed char, vector bool char);
     int vec_all_ge (vector signed char, vector signed char);
     int vec_all_ge (vector bool short, vector unsigned short);
     int vec_all_ge (vector unsigned short, vector bool short);
     int vec_all_ge (vector unsigned short, vector unsigned short);
     int vec_all_ge (vector signed short, vector signed short);
     int vec_all_ge (vector bool short, vector signed short);
     int vec_all_ge (vector signed short, vector bool short);
     int vec_all_ge (vector bool int, vector unsigned int);
     int vec_all_ge (vector unsigned int, vector bool int);
     int vec_all_ge (vector unsigned int, vector unsigned int);
     int vec_all_ge (vector bool int, vector signed int);
     int vec_all_ge (vector signed int, vector bool int);
     int vec_all_ge (vector signed int, vector signed int);
     int vec_all_ge (vector float, vector float);

     int vec_all_gt (vector bool char, vector unsigned char);
     int vec_all_gt (vector unsigned char, vector bool char);
     int vec_all_gt (vector unsigned char, vector unsigned char);
     int vec_all_gt (vector bool char, vector signed char);
     int vec_all_gt (vector signed char, vector bool char);
     int vec_all_gt (vector signed char, vector signed char);
     int vec_all_gt (vector bool short, vector unsigned short);
     int vec_all_gt (vector unsigned short, vector bool short);
     int vec_all_gt (vector unsigned short, vector unsigned short);
     int vec_all_gt (vector bool short, vector signed short);
     int vec_all_gt (vector signed short, vector bool short);
     int vec_all_gt (vector signed short, vector signed short);
     int vec_all_gt (vector bool int, vector unsigned int);
     int vec_all_gt (vector unsigned int, vector bool int);
     int vec_all_gt (vector unsigned int, vector unsigned int);
     int vec_all_gt (vector bool int, vector signed int);
     int vec_all_gt (vector signed int, vector bool int);
     int vec_all_gt (vector signed int, vector signed int);
     int vec_all_gt (vector float, vector float);

     int vec_all_in (vector float, vector float);

     int vec_all_le (vector bool char, vector unsigned char);
     int vec_all_le (vector unsigned char, vector bool char);
     int vec_all_le (vector unsigned char, vector unsigned char);
     int vec_all_le (vector bool char, vector signed char);
     int vec_all_le (vector signed char, vector bool char);
     int vec_all_le (vector signed char, vector signed char);
     int vec_all_le (vector bool short, vector unsigned short);
     int vec_all_le (vector unsigned short, vector bool short);
     int vec_all_le (vector unsigned short, vector unsigned short);
     int vec_all_le (vector bool short, vector signed short);
     int vec_all_le (vector signed short, vector bool short);
     int vec_all_le (vector signed short, vector signed short);
     int vec_all_le (vector bool int, vector unsigned int);
     int vec_all_le (vector unsigned int, vector bool int);
     int vec_all_le (vector unsigned int, vector unsigned int);
     int vec_all_le (vector bool int, vector signed int);
     int vec_all_le (vector signed int, vector bool int);
     int vec_all_le (vector signed int, vector signed int);
     int vec_all_le (vector float, vector float);

     int vec_all_lt (vector bool char, vector unsigned char);
     int vec_all_lt (vector unsigned char, vector bool char);
     int vec_all_lt (vector unsigned char, vector unsigned char);
     int vec_all_lt (vector bool char, vector signed char);
     int vec_all_lt (vector signed char, vector bool char);
     int vec_all_lt (vector signed char, vector signed char);
     int vec_all_lt (vector bool short, vector unsigned short);
     int vec_all_lt (vector unsigned short, vector bool short);
     int vec_all_lt (vector unsigned short, vector unsigned short);
     int vec_all_lt (vector bool short, vector signed short);
     int vec_all_lt (vector signed short, vector bool short);
     int vec_all_lt (vector signed short, vector signed short);
     int vec_all_lt (vector bool int, vector unsigned int);
     int vec_all_lt (vector unsigned int, vector bool int);
     int vec_all_lt (vector unsigned int, vector unsigned int);
     int vec_all_lt (vector bool int, vector signed int);
     int vec_all_lt (vector signed int, vector bool int);
     int vec_all_lt (vector signed int, vector signed int);
     int vec_all_lt (vector float, vector float);

     int vec_all_nan (vector float);

     int vec_all_ne (vector signed char, vector bool char);
     int vec_all_ne (vector signed char, vector signed char);
     int vec_all_ne (vector unsigned char, vector bool char);
     int vec_all_ne (vector unsigned char, vector unsigned char);
     int vec_all_ne (vector bool char, vector bool char);
     int vec_all_ne (vector bool char, vector unsigned char);
     int vec_all_ne (vector bool char, vector signed char);
     int vec_all_ne (vector signed short, vector bool short);
     int vec_all_ne (vector signed short, vector signed short);
     int vec_all_ne (vector unsigned short, vector bool short);
     int vec_all_ne (vector unsigned short, vector unsigned short);
     int vec_all_ne (vector bool short, vector bool short);
     int vec_all_ne (vector bool short, vector unsigned short);
     int vec_all_ne (vector bool short, vector signed short);
     int vec_all_ne (vector pixel, vector pixel);
     int vec_all_ne (vector signed int, vector bool int);
     int vec_all_ne (vector signed int, vector signed int);
     int vec_all_ne (vector unsigned int, vector bool int);
     int vec_all_ne (vector unsigned int, vector unsigned int);
     int vec_all_ne (vector bool int, vector bool int);
     int vec_all_ne (vector bool int, vector unsigned int);
     int vec_all_ne (vector bool int, vector signed int);
     int vec_all_ne (vector float, vector float);

     int vec_all_nge (vector float, vector float);

     int vec_all_ngt (vector float, vector float);

     int vec_all_nle (vector float, vector float);

     int vec_all_nlt (vector float, vector float);

     int vec_all_numeric (vector float);

     int vec_any_eq (vector signed char, vector bool char);
     int vec_any_eq (vector signed char, vector signed char);
     int vec_any_eq (vector unsigned char, vector bool char);
     int vec_any_eq (vector unsigned char, vector unsigned char);
     int vec_any_eq (vector bool char, vector bool char);
     int vec_any_eq (vector bool char, vector unsigned char);
     int vec_any_eq (vector bool char, vector signed char);
     int vec_any_eq (vector signed short, vector bool short);
     int vec_any_eq (vector signed short, vector signed short);
     int vec_any_eq (vector unsigned short, vector bool short);
     int vec_any_eq (vector unsigned short, vector unsigned short);
     int vec_any_eq (vector bool short, vector bool short);
     int vec_any_eq (vector bool short, vector unsigned short);
     int vec_any_eq (vector bool short, vector signed short);
     int vec_any_eq (vector pixel, vector pixel);
     int vec_any_eq (vector signed int, vector bool int);
     int vec_any_eq (vector signed int, vector signed int);
     int vec_any_eq (vector unsigned int, vector bool int);
     int vec_any_eq (vector unsigned int, vector unsigned int);
     int vec_any_eq (vector bool int, vector bool int);
     int vec_any_eq (vector bool int, vector unsigned int);
     int vec_any_eq (vector bool int, vector signed int);
     int vec_any_eq (vector float, vector float);

     int vec_any_ge (vector signed char, vector bool char);
     int vec_any_ge (vector unsigned char, vector bool char);
     int vec_any_ge (vector unsigned char, vector unsigned char);
     int vec_any_ge (vector signed char, vector signed char);
     int vec_any_ge (vector bool char, vector unsigned char);
     int vec_any_ge (vector bool char, vector signed char);
     int vec_any_ge (vector unsigned short, vector bool short);
     int vec_any_ge (vector unsigned short, vector unsigned short);
     int vec_any_ge (vector signed short, vector signed short);
     int vec_any_ge (vector signed short, vector bool short);
     int vec_any_ge (vector bool short, vector unsigned short);
     int vec_any_ge (vector bool short, vector signed short);
     int vec_any_ge (vector signed int, vector bool int);
     int vec_any_ge (vector unsigned int, vector bool int);
     int vec_any_ge (vector unsigned int, vector unsigned int);
     int vec_any_ge (vector signed int, vector signed int);
     int vec_any_ge (vector bool int, vector unsigned int);
     int vec_any_ge (vector bool int, vector signed int);
     int vec_any_ge (vector float, vector float);

     int vec_any_gt (vector bool char, vector unsigned char);
     int vec_any_gt (vector unsigned char, vector bool char);
     int vec_any_gt (vector unsigned char, vector unsigned char);
     int vec_any_gt (vector bool char, vector signed char);
     int vec_any_gt (vector signed char, vector bool char);
     int vec_any_gt (vector signed char, vector signed char);
     int vec_any_gt (vector bool short, vector unsigned short);
     int vec_any_gt (vector unsigned short, vector bool short);
     int vec_any_gt (vector unsigned short, vector unsigned short);
     int vec_any_gt (vector bool short, vector signed short);
     int vec_any_gt (vector signed short, vector bool short);
     int vec_any_gt (vector signed short, vector signed short);
     int vec_any_gt (vector bool int, vector unsigned int);
     int vec_any_gt (vector unsigned int, vector bool int);
     int vec_any_gt (vector unsigned int, vector unsigned int);
     int vec_any_gt (vector bool int, vector signed int);
     int vec_any_gt (vector signed int, vector bool int);
     int vec_any_gt (vector signed int, vector signed int);
     int vec_any_gt (vector float, vector float);

     int vec_any_le (vector bool char, vector unsigned char);
     int vec_any_le (vector unsigned char, vector bool char);
     int vec_any_le (vector unsigned char, vector unsigned char);
     int vec_any_le (vector bool char, vector signed char);
     int vec_any_le (vector signed char, vector bool char);
     int vec_any_le (vector signed char, vector signed char);
     int vec_any_le (vector bool short, vector unsigned short);
     int vec_any_le (vector unsigned short, vector bool short);
     int vec_any_le (vector unsigned short, vector unsigned short);
     int vec_any_le (vector bool short, vector signed short);
     int vec_any_le (vector signed short, vector bool short);
     int vec_any_le (vector signed short, vector signed short);
     int vec_any_le (vector bool int, vector unsigned int);
     int vec_any_le (vector unsigned int, vector bool int);
     int vec_any_le (vector unsigned int, vector unsigned int);
     int vec_any_le (vector bool int, vector signed int);
     int vec_any_le (vector signed int, vector bool int);
     int vec_any_le (vector signed int, vector signed int);
     int vec_any_le (vector float, vector float);

     int vec_any_lt (vector bool char, vector unsigned char);
     int vec_any_lt (vector unsigned char, vector bool char);
     int vec_any_lt (vector unsigned char, vector unsigned char);
     int vec_any_lt (vector bool char, vector signed char);
     int vec_any_lt (vector signed char, vector bool char);
     int vec_any_lt (vector signed char, vector signed char);
     int vec_any_lt (vector bool short, vector unsigned short);
     int vec_any_lt (vector unsigned short, vector bool short);
     int vec_any_lt (vector unsigned short, vector unsigned short);
     int vec_any_lt (vector bool short, vector signed short);
     int vec_any_lt (vector signed short, vector bool short);
     int vec_any_lt (vector signed short, vector signed short);
     int vec_any_lt (vector bool int, vector unsigned int);
     int vec_any_lt (vector unsigned int, vector bool int);
     int vec_any_lt (vector unsigned int, vector unsigned int);
     int vec_any_lt (vector bool int, vector signed int);
     int vec_any_lt (vector signed int, vector bool int);
     int vec_any_lt (vector signed int, vector signed int);
     int vec_any_lt (vector float, vector float);

     int vec_any_nan (vector float);

     int vec_any_ne (vector signed char, vector bool char);
     int vec_any_ne (vector signed char, vector signed char);
     int vec_any_ne (vector unsigned char, vector bool char);
     int vec_any_ne (vector unsigned char, vector unsigned char);
     int vec_any_ne (vector bool char, vector bool char);
     int vec_any_ne (vector bool char, vector unsigned char);
     int vec_any_ne (vector bool char, vector signed char);
     int vec_any_ne (vector signed short, vector bool short);
     int vec_any_ne (vector signed short, vector signed short);
     int vec_any_ne (vector unsigned short, vector bool short);
     int vec_any_ne (vector unsigned short, vector unsigned short);
     int vec_any_ne (vector bool short, vector bool short);
     int vec_any_ne (vector bool short, vector unsigned short);
     int vec_any_ne (vector bool short, vector signed short);
     int vec_any_ne (vector pixel, vector pixel);
     int vec_any_ne (vector signed int, vector bool int);
     int vec_any_ne (vector signed int, vector signed int);
     int vec_any_ne (vector unsigned int, vector bool int);
     int vec_any_ne (vector unsigned int, vector unsigned int);
     int vec_any_ne (vector bool int, vector bool int);
     int vec_any_ne (vector bool int, vector unsigned int);
     int vec_any_ne (vector bool int, vector signed int);
     int vec_any_ne (vector float, vector float);

     int vec_any_nge (vector float, vector float);

     int vec_any_ngt (vector float, vector float);

     int vec_any_nle (vector float, vector float);

     int vec_any_nlt (vector float, vector float);

     int vec_any_numeric (vector float);

     int vec_any_out (vector float, vector float);

SPARC VIS Built-in Functions
----------------------------

GCC supports SIMD operations on the SPARC using both the generic vector extensions (see Vector Extensions) as well as built-in functions for the SPARC Visual Instruction Set (VIS).  When you use the -mvis switch, the VIS extension is exposed as the following built-in functions:

     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef short v2hi __attribute__ ((vector_size (4)));
     typedef char v8qi __attribute__ ((vector_size (8)));
     typedef char v4qi __attribute__ ((vector_size (4)));

     void * __builtin_vis_alignaddr (void *, long);
     int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
     v2si __builtin_vis_faligndatav2si (v2si, v2si);
     v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
     v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);

     v4hi __builtin_vis_fexpand (v4qi);

     v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
     v4hi __builtin_vis_fmul8x16au (v4qi, v4hi);
     v4hi __builtin_vis_fmul8x16al (v4qi, v4hi);
     v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
     v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
     v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
     v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);

     v4qi __builtin_vis_fpack16 (v4hi);
     v8qi __builtin_vis_fpack32 (v2si, v2si);
     v2hi __builtin_vis_fpackfix (v2si);
     v8qi __builtin_vis_fpmerge (v4qi, v4qi);

     int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);

Format Checks Specific to Particular Target Machines
====================================================

For some target machines, GCC supports additional options to the format attribute (see Declaring Attributes of Functions).

Solaris Format Checks
---------------------

Solaris targets support the cmn_err (or __cmn_err__) format check.  cmn_err accepts a subset of the standard printf conversions, and the two-argument %b conversion for displaying bit-fields.  See the Solaris man page for cmn_err for more information.

Pragmas Accepted by GCC
=======================

GCC supports several types of pragmas, primarily in order to compile code originally written for other compilers.  Note that in general we do not recommend the use of pragmas; see Function Attributes, for further explanation.

ARM Pragmas
-----------

The ARM target defines pragmas for controlling the default addition of long_call and short_call attributes to functions. See Function Attributes, for information about the effects of these attributes.

long_calls
     Set all subsequent functions to have the long_call attribute.

no_long_calls
     Set all subsequent functions to have the short_call attribute.

long_calls_off
     Do not affect the long_call or short_call attributes of subsequent functions.

M32C Pragmas
------------

memregs NUMBER
     Overrides the command line option -memregs= for the current file.  Use with care!  This pragma must be before any function in the file, and mixing different memregs values in different objects may make them incompatible.  This pragma is useful when a performance-critical function uses a memreg for temporary values, as it may allow you to reduce the number of memregs used.

RS/6000 and PowerPC Pragmas
---------------------------

The RS/6000 and PowerPC targets define one pragma for controlling whether or not the longcall attribute is added to function declarations by default.  This pragma overrides the -mlongcall option, but not the longcall and shortcall attributes. See RS/6000 and PowerPC Options, for more information about when long calls are and are not necessary.

longcall (1)
     Apply the longcall attribute to all subsequent function declarations.

longcall (0)
     Do not apply the longcall attribute to subsequent function declarations.

Darwin Pragmas
--------------

The following pragmas are available for all architectures running the Darwin operating system.  These are useful for compatibility with other Mac OS compilers.

mark TOKENS...
     This pragma is accepted, but has no effect.

options align=ALIGNMENT
     This pragma sets the alignment of fields in structures.  The values of ALIGNMENT may be mac68k, to emulate m68k alignment, or power, to emulate PowerPC alignment.  Uses of this pragma nest properly; to restore the previous setting, use reset for the ALIGNMENT.

segment TOKENS...
     This pragma is accepted, but has no effect.

unused (VAR [, VAR]...)
     This pragma declares variables to be possibly unused.  GCC will not produce warnings for the listed variables.  The effect is similar to that of the unused attribute, except that this pragma may appear anywhere within the variables' scopes.

Solaris Pragmas
---------------

The Solaris target supports #pragma redefine_extname (see Symbol-Renaming Pragmas).  It also supports additional #pragma directives for compatibility with the system compiler.

align ALIGNMENT (VARIABLE [, VARIABLE]...)

     Increase the minimum alignment of each VARIABLE to ALIGNMENT. This is the same as GCC's aligned attribute see Variable Attributes).  Macro expansion occurs on the arguments to this pragma when compiling C and Objective-C.  It does not currently occur when compiling C++, but this is a bug which may be fixed in a future release.

fini (FUNCTION [, FUNCTION]...)

     This pragma causes each listed FUNCTION to be called after main, or during shared module unloading, by adding a call to the .fini section.

init (FUNCTION [, FUNCTION]...)

     This pragma causes each listed FUNCTION to be called during initialization (before main) or during shared module loading, by adding a call to the .init section.

Symbol-Renaming Pragmas
-----------------------

For compatibility with the Solaris and Tru64 UNIX system headers, GCC supports two #pragma directives which change the name used in assembly for a given declaration.  These pragmas are only available on platforms whose system headers need them.  To get this effect on all platforms supported by GCC, use the asm labels extension (see Asm Labels).

redefine_extname OLDNAME NEWNAME

     This pragma gives the C function OLDNAME the assembly symbol NEWNAME.  The preprocessor macro __PRAGMA_REDEFINE_EXTNAME will be defined if this pragma is available (currently only on Solaris).

extern_prefix STRING

     This pragma causes all subsequent external function and variable declarations to have STRING prepended to their assembly symbols. This effect may be terminated with another extern_prefix pragma whose argument is an empty string.  The preprocessor macro __PRAGMA_EXTERN_PREFIX will be defined if this pragma is available (currently only on Tru64 UNIX).

These pragmas and the asm labels extension interact in a complicated manner.  Here are some corner cases you may want to be aware of.

 1. Both pragmas silently apply only to declarations with external linkage.  Asm labels do not have this restriction.

 2. In C++, both pragmas silently apply only to declarations with ``C'' linkage.  Again, asm labels do not have this restriction.

 3. If any of the three ways of changing the assembly name of a declaration is applied to a declaration whose assembly name has already been determined (either by a previous use of one of these features, or because the compiler needed the assembly name in order to generate code), and the new name is different, a warning issues and the name does not change.

 4. The OLDNAME used by #pragma redefine_extname is always the C-language name.

 5. If #pragma extern_prefix is in effect, and a declaration occurs with an asm label attached, the prefix is silently ignored for that declaration.

 6. If #pragma extern_prefix and #pragma redefine_extname apply to the same declaration, whichever triggered first wins, and a warning issues if they contradict each other.  (We would like to have #pragma redefine_extname always win, for consistency with asm labels, but if #pragma extern_prefix triggers first we have no way of knowing that that happened.)

Structure-Packing Pragmas
-------------------------

For compatibility with Win32, GCC supports a set of #pragma directives which change the maximum alignment of members of structures (other than zero-width bitfields), unions, and classes subsequently defined.  The N value below always is required to be a small power of two and specifies the new alignment in bytes.

 1. #pragma pack(N) simply sets the new alignment.

 2. #pragma pack() sets the alignment to the one that was in effect when compilation started (see also command line option -fpack-struct[=<n>] see Code Gen Options).

 3. #pragma pack(push[,N]) pushes the current alignment setting on an internal stack and then optionally sets the new alignment.

 4. #pragma pack(pop) restores the alignment setting to the one saved at the top of the internal stack (and removes that stack entry). Note that #pragma pack([N]) does not influence this internal stack; thus it is possible to have #pragma pack(push) followed by multiple #pragma pack(N) instances and finalized by a single #pragma pack(pop).

Some targets, e.g. i386 and powerpc, support the ms_struct #pragma which lays out a structure as the documented __attribute__ ((ms_struct)).

 1. #pragma ms_struct on turns on the layout for structures declared.

 2. #pragma ms_struct off turns off the layout for structures declared.

 3. #pragma ms_struct reset goes back to the default layout.

Weak Pragmas
------------

For compatibility with SVR4, GCC supports a set of #pragma directives for declaring symbols to be weak, and defining weak aliases.

#pragma weak SYMBOL
     This pragma declares SYMBOL to be weak, as if the declaration had the attribute of the same name.  The pragma may appear before or after the declaration of SYMBOL, but must appear before either its first use or its definition.  It is not an error for SYMBOL to never be defined at all.

#pragma weak SYMBOL1 = SYMBOL2
     This pragma declares SYMBOL1 to be a weak alias of SYMBOL2. It is an error if SYMBOL2 is not defined in the current translation unit.

Diagnostic Pragmas
------------------

GCC allows the user to selectively enable or disable certain types of diagnostics, and change the kind of the diagnostic.  For example, a project's policy might require that all sources compile with -Werror but certain files might have exceptions allowing specific types of warnings.  Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.

#pragma GCC diagnostic KIND OPTION

     Modifies the disposition of a diagnostic.  Note that not all diagnostics are modifiable; at the moment only warnings (normally controlled by -W...) can be controlled, and not all of them. Use -fdiagnostics-show-option to determine which diagnostics are controllable and which option controls them.

     KIND is error to treat this diagnostic as an error, warning to treat it like a warning (even if -Werror is in effect), or ignored if the diagnostic is to be ignored. OPTION is a double quoted string which matches the command line option.

          #pragma GCC diagnostic warning "-Wformat"
          #pragma GCC diagnostic error "-Wformat"
          #pragma GCC diagnostic ignored "-Wformat"

     Note that these pragmas override any command line options.  Also, while it is syntactically valid to put these pragmas anywhere in your sources, the only supported location for them is before any data or functions are defined.  Doing otherwise may result in unpredictable results depending on how the optimizer manages your sources.  If the same option is listed multiple times, the last one specified is the one that is in effect.  This pragma is not intended to be a general purpose replacement for command line options, but for implementing strict control over project policies.

Visibility Pragmas
------------------

#pragma GCC visibility push(VISIBILITY)
#pragma GCC visibility pop

     This pragma allows the user to set the visibility for multiple declarations without having to give each a visibility attribute see Function Attributes, for more information about visibility and the attribute syntax.

     In C++, #pragma GCC visibility affects only namespace-scope declarations.  Class members and template specializations are not affected; if you want to override the visibility for a particular member or instantiation, you must use an attribute.

Unnamed struct/union fields within structs/unions
=================================================

For compatibility with other compilers, GCC allows you to define a structure or union that contains, as fields, structures and unions without names.  For example:

     struct {
       int a;
       union {
         int b;
         float c;
       };
       int d;
     } foo;

In this example, the user would be able to access members of the unnamed union with code like foo.b.  Note that only unnamed structs and unions are allowed, you may not have, for example, an unnamed int.

You must never create such structures that cause ambiguous field definitions. For example, this structure:

     struct {
       int a;
       struct {
         int a;
       };
     } foo;

It is ambiguous which a is being referred to with foo.a. Such constructs are not supported and must be avoided.  In the future, such constructs may be detected and treated as compilation errors.

Unless -fms-extensions is used, the unnamed field must be a structure or union definition without a tag (for example, struct { int a; };).  If -fms-extensions is used, the field may also be a definition with a tag such as struct foo { int a; };, a reference to a previously defined structure or union such as struct foo;, or a reference to a typedef name for a previously defined structure or union type.

Thread-Local Storage
====================

Thread-local storage (TLS) is a mechanism by which variables are allocated such that there is one instance of the variable per extant thread.  The run-time model GCC uses to implement this originates in the IA-64 processor-specific ABI, but has since been migrated to other processors as well.  It requires significant support from the linker (ld), dynamic linker (ld.so), and system libraries (libc.so and libpthread.so), so it is not available everywhere.

At the user level, the extension is visible with a new storage class keyword: __thread.  For example:

     __thread int i;
     extern __thread struct state s;
     static __thread char *p;

The __thread specifier may be used alone, with the extern or static specifiers, but with no other storage class specifier. When used with extern or static, __thread must appear immediately after the other storage class specifier.

The __thread specifier may be applied to any global, file-scoped static, function-scoped static, or static data member of a class.  It may not be applied to block-scoped automatic or non-static data member.

When the address-of operator is applied to a thread-local variable, it is evaluated at run-time and returns the address of the current thread's instance of that variable.  An address so obtained may be used by any thread.  When a thread terminates, any pointers to thread-local variables in that thread become invalid.

No static initialization may refer to the address of a thread-local variable.

In C++, if an initializer is present for a thread-local variable, it must be a CONSTANT-EXPRESSION, as defined in 5.19.2 of the ANSI/ISO C++ standard.

See ELF Handling For Thread-Local Storage (http://people.redhat.com/drepper/tls.pdf) for a detailed explanation of the four thread-local storage addressing models, and how the run-time is expected to function.

ISO/IEC 9899:1999 Edits for Thread-Local Storage
------------------------------------------------

The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the exact semantics of the language extension.

  * 5.1.2  Execution environments

     Add new text after paragraph 1

          Within either execution environment, a thread is a flow of control within a program.  It is implementation defined whether or not there may be more than one thread associated with a program. It is implementation defined how threads beyond the first are created, the name and type of the function called at thread startup, and how threads may be terminated.  However, objects with thread storage duration shall be initialized before thread startup.

  * 6.2.4  Storage durations of objects

     Add new text before paragraph 3

          An object whose identifier is declared with the storage-class specifier __thread has thread storage duration. Its lifetime is the entire execution of the thread, and its stored value is initialized only once, prior to thread startup.

  * 6.4.1  Keywords

     Add __thread.

  * 6.7.1  Storage-class specifiers

     Add __thread to the list of storage class specifiers in paragraph 1.

     Change paragraph 2 to

          With the exception of __thread, at most one storage-class specifier may be given [...].  The __thread specifier may be used alone, or immediately following extern or static.

     Add new text after paragraph 6

          The declaration of an identifier for a variable that has block scope that specifies __thread shall also specify either extern or static.

          The __thread specifier shall be used only with variables.

ISO/IEC 14882:1998 Edits for Thread-Local Storage
-------------------------------------------------

The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) that document the exact semantics of the language extension.

  * [intro.execution]

     New text after paragraph 4

          A thread is a flow of control within the abstract machine. It is implementation defined whether or not there may be more than one thread.

     New text after paragraph 7

          It is unspecified whether additional action must be taken to ensure when and whether side effects are visible to other threads.

  * [lex.key]

     Add __thread.

  * [basic.start.main]

     Add after paragraph 5

          The thread that begins execution at the main function is called the main thread.  It is implementation defined how functions beginning threads other than the main thread are designated or typed. A function so designated, as well as the main function, is called a thread startup function.  It is implementation defined what happens if a thread startup function returns.  It is implementation defined what happens to other threads when any thread calls exit.

  * [basic.start.init]

     Add after paragraph 4

          The storage for an object of thread storage duration shall be statically initialized before the first statement of the thread startup function.  An object of thread storage duration shall not require dynamic initialization.

  * [basic.start.term]

     Add after paragraph 3

          The type of an object with thread storage duration shall not have a non-trivial destructor, nor shall it be an array type whose elements (directly or indirectly) have non-trivial destructors.

  * [basic.stc]

     Add ``thread storage duration'' to the list in paragraph 1.

     Change paragraph 2

          Thread, static, and automatic storage durations are associated with objects introduced by declarations [...].

     Add __thread to the list of specifiers in paragraph 3.

  * [basic.stc.thread]

     New section before [basic.stc.static]

          The keyword __thread applied to a non-local object gives the object thread storage duration.

          A local variable or class data member declared both static and __thread gives the variable or member thread storage duration.

  * [basic.stc.static]

     Change paragraph 1

          All objects which have neither thread storage duration, dynamic storage duration nor are local [...].

  * [dcl.stc]

     Add __thread to the list in paragraph 1.

     Change paragraph 1

          With the exception of __thread, at most one STORAGE-CLASS-SPECIFIER shall appear in a given DECL-SPECIFIER-SEQ.  The __thread specifier may be used alone, or immediately following the extern or static specifiers.  [...]

     Add after paragraph 5

          The __thread specifier can be applied only to the names of objects and to anonymous unions.

  * [class.mem]

     Add after paragraph 6

          Non-static members shall not be __thread.

Extensions to the C++ Language
******************************

The GNU compiler provides these extensions to the C++ language (and you can also use most of the C language extensions in your C++ programs).  If you want to write code that checks whether these features are available, you can test for the GNU compiler the same way as for C programs: check for a predefined macro __GNUC__.  You can also use __GNUG__ to test specifically for GNU C++ (see Predefined Macros (The GNU C Preprocessor)).

When is a Volatile Object Accessed?
===================================

Both the C and C++ standard have the concept of volatile objects.  These are normally accessed by pointers and used for accessing hardware.  The standards encourage compilers to refrain from optimizations concerning accesses to volatile objects.  The C standard leaves it implementation defined  as to what constitutes a volatile access.  The C++ standard omits to specify this, except to say that C++ should behave in a similar manner to C with respect to volatiles, where possible.  The minimum either standard specifies is that at a sequence point all previous accesses to volatile objects have stabilized and no subsequent accesses have occurred.  Thus an implementation is free to reorder and combine volatile accesses which occur between sequence points, but cannot do so for accesses across a sequence point.  The use of volatiles does not allow you to violate the restriction on updating objects multiple times within a sequence point.

See Volatile qualifier and the C compiler.

The behavior differs slightly between C and C++ in the non-obvious cases:

     volatile int *src = SOMEVALUE;
     *src;

With C, such expressions are rvalues, and GCC interprets this either as a read of the volatile object being pointed to or only as request to evaluate the side-effects.  The C++ standard specifies that such expressions do not undergo lvalue to rvalue conversion, and that the type of the dereferenced object may be incomplete.  The C++ standard does not specify explicitly that it is this lvalue to rvalue conversion which may be responsible for causing an access.  However, there is reason to believe that it is, because otherwise certain simple expressions become undefined.  However, because it would surprise most programmers, G++ treats dereferencing a pointer to volatile object of complete type when the value is unused as GCC would do for an equivalent type in C.  When the object has incomplete type, G++ issues a warning; if you wish to force an error, you must force a conversion to rvalue with, for instance, a static cast.

When using a reference to volatile, G++ does not treat equivalent expressions as accesses to volatiles, but instead issues a warning that no volatile is accessed.  The rationale for this is that otherwise it becomes difficult to determine where volatile access occur, and not possible to ignore the return value from functions returning volatile references.  Again, if you wish to force a read, cast the reference to an rvalue.

Restricting Pointer Aliasing
============================

As with the C front end, G++ understands the C99 feature of restricted pointers, specified with the __restrict__, or __restrict type qualifier.  Because you cannot compile C++ by specifying the -std=c99 language flag, restrict is not a keyword in C++.

In addition to allowing restricted pointers, you can specify restricted references, which indicate that the reference is not aliased in the local context.

     void fn (int *__restrict__ rptr, int &__restrict__ rref)
     {
       /* ... */
     }

In the body of fn, RPTR points to an unaliased integer and RREF refers to a (different) unaliased integer.

You may also specify whether a member function's THIS pointer is unaliased by using __restrict__ as a member function qualifier.

     void T::fn () __restrict__
     {
       /* ... */
     }

Within the body of T::fn, THIS will have the effective definition T *__restrict__ const this.  Notice that the interpretation of a __restrict__ member function qualifier is different to that of const or volatile qualifier, in that it is applied to the pointer rather than the object.  This is consistent with other compilers which implement restricted pointers.

As with all outermost parameter qualifiers, __restrict__ is ignored in function definition matching.  This means you only need to specify __restrict__ in a function definition, rather than in a function prototype as well.

Vague Linkage
=============

There are several constructs in C++ which require space in the object file but are not clearly tied to a single translation unit.  We say that these constructs have ``vague linkage''.  Typically such constructs are emitted wherever they are needed, though sometimes we can be more clever.

Inline Functions
     Inline functions are typically defined in a header file which can be included in many different compilations.  Hopefully they can usually be inlined, but sometimes an out-of-line copy is necessary, if the address of the function is taken or if inlining fails.  In general, we emit an out-of-line copy in all translation units where one is needed.  As an exception, we only emit inline virtual functions with the vtable, since it will always require a copy.

     Local static variables and string constants used in an inline function are also considered to have vague linkage, since they must be shared between all inlined and out-of-line instances of the function.

VTables
     C++ virtual functions are implemented in most compilers using a lookup table, known as a vtable.  The vtable contains pointers to the virtual functions provided by a class, and each object of the class contains a pointer to its vtable (or vtables, in some multiple-inheritance situations).  If the class declares any non-inline, non-pure virtual functions, the first one is chosen as the ``key method'' for the class, and the vtable is only emitted in the translation unit where the key method is defined.

     Note: If the chosen key method is later defined as inline, the vtable will still be emitted in every translation unit which defines it. Make sure that any inline virtuals are declared inline in the class body, even if they are not defined there.

type_info objects
     C++ requires information about types to be written out in order to implement dynamic_cast, typeid and exception handling. For polymorphic classes (classes with virtual functions), the type_info object is written out along with the vtable so that dynamic_cast can determine the dynamic type of a class object at runtime.  For all other types, we write out the type_info object when it is used: when applying typeid to an expression, throwing an object, or referring to a type in a catch clause or exception specification.

Template Instantiations
     Most everything in this section also applies to template instantiations, but there are other options as well. See Where's the Template?.

When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of these constructs will be discarded at link time.  This is known as COMDAT support.

On targets that don't support COMDAT, but do support weak symbols, GCC will use them.  This way one copy will override all the others, but the unused copies will still take up space in the executable.

For targets which do not support either COMDAT or weak symbols, most entities with vague linkage will be emitted as local symbols to avoid duplicate definition errors from the linker.  This will not happen for local statics in inlines, however, as having multiple copies will almost certainly break things.

See Declarations and Definitions in One Header, for another way to control placement of these constructs.

#pragma interface and implementation
====================================

#pragma interface and #pragma implementation provide the user with a way of explicitly directing the compiler to emit entities with vague linkage (and debugging information) in a particular translation unit.

Note: As of GCC 2.7.2, these #pragmas are not useful in most cases, because of COMDAT support and the ``key method'' heuristic mentioned in Vague Linkage.  Using them can actually cause your program to grow due to unnecessary out-of-line copies of inline functions.  Currently (3.4) the only benefit of these #pragmas is reduced duplication of debugging information, and that should be addressed soon on DWARF 2 targets with the use of COMDAT groups.

#pragma interface
#pragma interface "SUBDIR/OBJECTS.h"
     Use this directive in header files that define object classes, to save space in most of the object files that use those classes.  Normally, local copies of certain information (backup copies of inline member functions, debugging information, and the internal tables that implement virtual functions) must be kept in each object file that includes class definitions.  You can use this pragma to avoid such duplication.  When a header file containing #pragma interface is included in a compilation, this auxiliary information will not be generated (unless the main input source file itself uses #pragma implementation). Instead, the object files will contain references to be resolved at link time.

     The second form of this directive is useful for the case where you have multiple headers with the same name in different directories.  If you use this form, you must specify the same string to #pragma implementation.

#pragma implementation
#pragma implementation "OBJECTS.h"
     Use this pragma in a main input file, when you want full output from included header files to be generated (and made globally visible).  The included header file, in turn, should use #pragma interface. Backup copies of inline member functions, debugging information, and the internal tables used to implement virtual functions are all generated in implementation files.

     If you use #pragma implementation with no argument, it applies to an include file with the same basename (A file's basename was the name stripped of all leading path information and of trailing suffixes, such as .h or .C or .cc.) as your source file.  For example, in allclass.cc, giving just #pragma implementation by itself is equivalent to #pragma implementation "allclass.h".

     In versions of GNU C++ prior to 2.6.0 allclass.h was treated as an implementation file whenever you would include it from allclass.cc even if you never specified #pragma implementation.  This was deemed to be more trouble than it was worth, however, and disabled.

     Use the string argument if you want a single implementation file to include code from multiple header files.  (You must also use #include to include the header file; #pragma implementation only specifies how to use the file---it doesn't actually include it.)

     There is no way to split up the contents of a single header file into multiple implementation files.

#pragma implementation and #pragma interface also have an effect on function inlining.

If you define a class in a header file marked with #pragma interface, the effect on an inline function defined in that class is similar to an explicit extern declaration---the compiler emits no code at all to define an independent version of the function.  Its definition is used only for inlining with its callers.

Conversely, when you include the same header file in a main source file that declares it as #pragma implementation, the compiler emits code for the function itself; this defines a version of the function that can be found via pointers (or by callers compiled without inlining).  If all calls to the function can be inlined, you can avoid emitting the function by compiling with -fno-implement-inlines. If any calls were not inlined, you will get linker errors.

Where's the Template?
=====================

C++ templates are the first language feature to require more intelligence from the environment than one usually finds on a UNIX system.  Somehow the compiler and linker have to make sure that each template instance occurs exactly once in the executable if it is needed, and not at all otherwise.  There are two basic approaches to this problem, which are referred to as the Borland model and the Cfront model.

Borland model
     Borland C++ solved the template instantiation problem by adding the code equivalent of common blocks to their linker; the compiler emits template instances in each translation unit that uses them, and the linker collapses them together.  The advantage of this model is that the linker only has to consider the object files themselves; there is no external complexity to worry about.  This disadvantage is that compilation time is increased because the template code is being compiled repeatedly. Code written for this model tends to include definitions of all templates in the header file, since they must be seen to be instantiated.

Cfront model
     The AT&T C++ translator, Cfront, solved the template instantiation problem by creating the notion of a template repository, an automatically maintained place where template instances are stored.  A more modern version of the repository works as follows: As individual object files are built, the compiler places any template definitions and instantiations encountered in the repository.  At link time, the link wrapper adds in the objects in the repository and compiles any needed instances that were not previously emitted.  The advantages of this model are more optimal compilation speed and the ability to use the system linker; to implement the Borland model a compiler vendor also needs to replace the linker.  The disadvantages are vastly increased complexity, and thus potential for error; for some code this can be just as transparent, but in practice it can been very difficult to build multiple programs in one directory and one program in multiple directories.  Code written for this model tends to separate definitions of non-inline member templates into a separate file, which should be compiled separately.

When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the Borland model.  On other systems, G++ implements neither automatic model.

A future version of G++ will support a hybrid model whereby the compiler will emit any instantiations for which the template definition is included in the compile, and store template definitions and instantiation context information into the object file for the rest. The link wrapper will extract that information as necessary and invoke the compiler to produce the remaining instantiations.  The linker will then combine duplicate instantiations.

In the mean time, you have the following options for dealing with template instantiations:

 1. Compile your template-using code with -frepo.  The compiler will generate files with the extension .rpo listing all of the template instantiations used in the corresponding object files which could be instantiated there; the link wrapper, collect2, will then update the .rpo files to tell the compiler where to place those instantiations and rebuild any affected object files.  The link-time overhead is negligible after the first pass, as the compiler will continue to place the instantiations in the same files.

     This is your best option for application code written for the Borland model, as it will just work.  Code written for the Cfront model will need to be modified so that the template definitions are available at one or more points of instantiation; usually this is as simple as adding #include <tmethods.cc> to the end of each template header.

     For library code, if you want the library to provide all of the template instantiations it needs, just try to link all of its object files together; the link will fail, but cause the instantiations to be generated as a side effect.  Be warned, however, that this may cause conflicts if multiple libraries try to provide the same instantiations. For greater control, use explicit instantiation as described in the next option.

 2. Compile your code with -fno-implicit-templates to disable the implicit generation of template instances, and explicitly instantiate all the ones you use.  This approach requires more knowledge of exactly which instances you need than do the others, but it's less mysterious and allows greater control.  You can scatter the explicit instantiations throughout your program, perhaps putting them in the translation units where the instances are used or the translation units that define the templates themselves; you can put all of the explicit instantiations you need into one big file; or you can create small files like

          #include "Foo.h"
          #include "Foo.cc"

          template class Foo<int>;
          template ostream& operator <<
                          (ostream&, const Foo<int>&);

     for each of the instances you need, and create a template instantiation library from those.

     If you are using Cfront-model code, you can probably get away with not using -fno-implicit-templates when compiling files that don't #include the member template definitions.

     If you use one big file to do the instantiations, you may want to compile it without -fno-implicit-templates so you get all of the instances required by your explicit instantiations (but not by any other files) without having to specify them as well.

     G++ has extended the template instantiation syntax given in the ISO standard to allow forward declaration of explicit instantiations (with extern), instantiation of the compiler support data for a template class (i.e. the vtable) without instantiating any of its members (with inline), and instantiation of only the static data members of a template class, without the support data or member functions (with (static):

          extern template int max (int, int);
          inline template class Foo<int>;
          static template class Foo<int>;

 3. Do nothing.  Pretend G++ does implement automatic instantiation management.  Code written for the Borland model will work fine, but each translation unit will contain instances of each of the templates it uses.  In a large program, this can lead to an unacceptable amount of code duplication.

Extracting the function pointer from a bound pointer to member function
=======================================================================

In C++, pointer to member functions (PMFs) are implemented using a wide pointer of sorts to handle all the possible call mechanisms; the PMF needs to store information about how to adjust the this pointer, and if the function pointed to is virtual, where to find the vtable, and where in the vtable to look for the member function.  If you are using PMFs in an inner loop, you should really reconsider that decision.  If that is not an option, you can extract the pointer to the function that would be called for a given object/PMF pair and call it directly inside the inner loop, to save a bit of time.

Note that you will still be paying the penalty for the call through a function pointer; on most modern architectures, such a call defeats the branch prediction features of the CPU.  This is also true of normal virtual function calls.

The syntax for this extension is

     extern A a;
     extern int (A::*fp)();
     typedef int (*fptr)(A *);

     fptr p = (fptr)(a.*fp);

For PMF constants (i.e. expressions of the form &Klasse::Member), no object is needed to obtain the address of the function.  They can be converted to function pointers directly:

     fptr p1 = (fptr)(&A::foo);

You must specify -Wno-pmf-conversions to use this extension.

C++-Specific Variable, Function, and Type Attributes
====================================================

Some attributes only make sense for C++ programs.

init_priority (PRIORITY)

     In Standard C++, objects defined at namespace scope are guaranteed to be initialized in an order in strict accordance with that of their definitions in a given translation unit.  No guarantee is made for initializations across translation units.  However, GNU C++ allows users to control the order of initialization of objects defined at namespace scope with the init_priority attribute by specifying a relative PRIORITY, a constant integral expression currently bounded between 101 and 65535 inclusive.  Lower numbers indicate a higher priority.

     In the following example, A would normally be created before B, but the init_priority attribute has reversed that order:

          Some_Class  A  __attribute__ ((init_priority (2000)));
          Some_Class  B  __attribute__ ((init_priority (543)));

     Note that the particular values of PRIORITY do not matter; only their relative ordering.

java_interface

     This type attribute informs C++ that the class is a Java interface.  It may only be applied to classes declared within an extern "Java" block. Calls to methods declared in this interface will be dispatched using GCJ's interface table mechanism, instead of regular virtual table dispatch.

See also Namespace Association.

Namespace Association
=====================

Caution: The semantics of this extension are not fully defined.  Users should refrain from using this extension as its semantics may change subtly over time.  It is possible that this extension will be removed in future versions of G++.

A using-directive with __attribute ((strong)) is stronger than a normal using-directive in two ways:

  * Templates from the used namespace can be specialized and explicitly instantiated as though they were members of the using namespace.

  * The using namespace is considered an associated namespace of all templates in the used namespace for purposes of argument-dependent name lookup.

The used namespace must be nested within the using namespace so that normal unqualified lookup works properly.

This is useful for composing a namespace transparently from implementation namespaces.  For example:

     namespace std {
       namespace debug {
         template <class T> struct A { };
       }
       using namespace debug __attribute ((__strong__));
       template <> struct A<int> { };   // ok to specialize

       template <class T> void f (A<T>);
     }

     int main()
     {
       f (std::A<float>());             // lookup finds std::f
       f (std::A<int>());
     }

Java Exceptions
===============

The Java language uses a slightly different exception handling model from C++.  Normally, GNU C++ will automatically detect when you are writing C++ code that uses Java exceptions, and handle them appropriately.  However, if C++ code only needs to execute destructors when Java exceptions are thrown through it, GCC will guess incorrectly. Sample problematic code is:

       struct S { ~S(); };
       extern void bar();    // is written in Java, and may throw exceptions
       void foo()
       {
         S s;
         bar();
       }

The usual effect of an incorrect guess is a link failure, complaining of a missing routine called __gxx_personality_v0.

You can inform the compiler that Java exceptions are to be used in a translation unit, irrespective of what it might think, by writing #pragma GCC java_exceptions at the head of the file.  This #pragma must appear before any functions that throw or catch exceptions, or run destructors when exceptions are thrown through them.

You cannot mix Java and C++ exceptions in the same translation unit.  It is believed to be safe to throw a C++ exception from one file through another file compiled for the Java exception model, or vice versa, but there may be bugs in this area.

Deprecated Features
===================

In the past, the GNU C++ compiler was extended to experiment with new features, at a time when the C++ language was still evolving.  Now that the C++ standard is complete, some of those features are superseded by superior alternatives.  Using the old features might cause a warning in some cases that the feature will be dropped in the future.  In other cases, the feature might be gone already.

While the list below is not exhaustive, it documents some of the options that are now deprecated:

-fexternal-templates
-falt-external-templates
     These are two of the many ways for G++ to implement template instantiation.  See Template Instantiation.  The C++ standard clearly defines how template definitions have to be organized across implementation units.  G++ has an implicit instantiation mechanism that should work just fine for standard-conforming code.

-fstrict-prototype
-fno-strict-prototype
     Previously it was possible to use an empty prototype parameter list to indicate an unspecified number of parameters (like C), rather than no parameters, as C++ demands.  This feature has been removed, except where it is required for backwards compatibility see Backwards Compatibility.

G++ allows a virtual function returning void * to be overridden by one returning a different pointer type.  This extension to the covariant return type rules is now deprecated and will be removed from a future version.

The G++ minimum and maximum operators (<? and >?) and their compound forms (<?=) and >?=) have been deprecated and will be removed in a future version.  Code using these operators should be modified to use std::min and std::max instead.

The named return value extension has been deprecated, and is now removed from G++.

The use of initializer lists with new expressions has been deprecated, and is now removed from G++.

Floating and complex non-type template parameters have been deprecated, and are now removed from G++.

The implicit typename extension has been deprecated and is now removed from G++.

The use of default arguments in function pointers, function typedefs and other places where they are not permitted by the standard is deprecated and will be removed from a future version of G++.

G++ allows floating-point literals to appear in integral constant expressions, e.g.  enum E { e = int(2.2 * 3.7) } This extension is deprecated and will be removed from a future version.

G++ allows static data members of const floating-point type to be declared with an initializer in a class definition. The standard only allows initializers for static members of const integral types and const enumeration types so this extension has been deprecated and will be removed from a future version.

Backwards Compatibility
=======================

Now that there is a definitive ISO standard C++, G++ has a specification to adhere to.  The C++ language evolved over time, and features that used to be acceptable in previous drafts of the standard, such as the ARM [Annotated C++ Reference Manual], are no longer accepted.  In order to allow compilation of C++ written to such drafts, G++ contains some backwards compatibilities.  All such backwards compatibility features are liable to disappear in future versions of G++. They should be considered deprecated see Deprecated Features.

For scope
     If a variable is declared at for scope, it used to remain in scope until the end of the scope which contained the for statement (rather than just within the for scope).  G++ retains this, but issues a warning, if such a variable is accessed outside the for scope.

Implicit C language
     Old C system header files did not contain an extern "C" {...} scope to set the language.  On such systems, all header files are implicitly scoped inside a C language scope.  Also, an empty prototype () will be treated as an unspecified number of arguments, rather than no arguments, as C++ demands.