/* Copyright (C) 1992, 1993, 2000 artofcode LLC.  All rights reserved.
  
  This program is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the
  Free Software Foundation; either version 2 of the License, or (at your
  option) any later version.

  This program is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  General Public License for more details.

  You should have received a copy of the GNU General Public License along
  with this program; if not, write to the Free Software Foundation, Inc.,
  59 Temple Place, Suite 330, Boston, MA, 02111-1307.

*/

/*$Id: gxfrac.h,v 1.3.4.1.2.1 2003/01/17 00:49:03 giles Exp $ */
/* Fraction representation for Ghostscript */

#ifndef gxfrac_INCLUDED
#  define gxfrac_INCLUDED

/*
 * Represent a fraction in [0.0..1.0].  Note that the 1.0 endpoint is
 * included.  Since undercolor removal requires a signed frac, we limit
 * fracs to 15 bits rather than 16.
 */
typedef short frac;
typedef short signed_frac;

#define arch_log2_sizeof_frac arch_log2_sizeof_short
#define arch_sizeof_frac arch_sizeof_short
#define frac_bits 15
#define frac_0 ((frac)0)

/*
 * Normally one would represent a fractional value of this kind as a short
 * integer, in [-32767..32767].  Unfortunately, this approach cannot
 * represent any of the common values like 1/2, 1/3, or 1/5 exactly, causing
 * rounding errors.  Instead, we opt for using the range [-32760..32760],
 * which allows exact representation of almost all commonly used fractions
 * (e.g., N/360 for 0<=N<=360).
 */
#define frac_1_0bits 3
#define frac_1 ((frac)0x7ff8)
#define frac_1_long ((long)frac_1)
#define frac_1_float ((float)frac_1)
/* Conversion between fracs and floats. */
#define frac2float(fr) ((fr) / frac_1_float)
#define float2frac(fl) ((frac)(((fl) + 0.5 / frac_1_float) * frac_1_float))

/*
 * Conversion between unsigned fracs and bytes (or, in general,
 * shorter integers) representing fractions. This is highly dependent
 * on the definition of frac_1 above.
 */
#define _frac2s(fr)\
  (((fr) >> (frac_bits - frac_1_0bits)) + (fr))
#define frac2bits(fr, nb)\
  ((uint)(_frac2s(fr) >> (frac_bits - (nb))))
#define frac2byte(fr) ((byte)frac2bits(fr, 8))
/* bits2frac requires frac_bits / 2 <= nb <= frac_bits. */
#define bits2frac(v, nb) ((frac)(\
  ((frac)(v) << (frac_bits - (nb))) +\
   ((v) >> ((nb) * 2 - frac_bits)) -\
   ((v) >> ((nb) - frac_1_0bits)) ))
#define byte2frac(b) bits2frac(b, 8)
/* Produce a result that is guaranteed to convert back to a frac */
/* not exceeding the original value fr. */
#define frac2bits_floor(fr, nb)\
  ((uint)((_frac2s(fr) - (_frac2s(fr) >> (nb))) >> (frac_bits - (nb))))
/*
 * Conversion between fracs and unsigned shorts.
 */
#define ushort_bits (arch_sizeof_short * 8)
#define frac2ushort(fr) ((ushort)(\
  ((fr) << (ushort_bits - frac_bits)) +\
  ((fr) >> (frac_bits * 2 - ushort_bits - frac_1_0bits)) ))
#define ushort2frac(us) ((frac)(\
  ((us) >> (ushort_bits - frac_bits)) -\
  ((us) >> (ushort_bits - frac_1_0bits)) ))
/*
 * Compute the quotient Q = floor(P / frac_1),
 * where P is the (ulong) product of a uint or ushort V and a frac F.
 * See gxarith.h for the underlying algorithm.
 */
#define frac_1_quo(p)\
  ( (((p) >> frac_1_0bits) + ((p) >> frac_bits) + 1) >> (frac_bits - frac_1_0bits) )
/*
 * Compute the remainder similarly, having already computed the quotient.
 * This is, of course, P - Q * frac_1.
 */
#define frac_1_rem(p, q)\
  ((frac)( (uint)(p) - ((q) << frac_bits) + ((q) << frac_1_0bits) ))

#endif /* gxfrac_INCLUDED */