dnl  AMD K6 mpn_divexact_by3 -- mpn division by 3, expecting no remainder.

dnl  Copyright 2000, 2001, 2002 Free Software Foundation, Inc.
dnl
dnl  This file is part of the GNU MP Library.
dnl
dnl  The GNU MP Library is free software; you can redistribute it and/or
dnl  modify it under the terms of the GNU Lesser General Public License as
dnl  published by the Free Software Foundation; either version 3 of the
dnl  License, or (at your option) any later version.
dnl
dnl  The GNU MP Library is distributed in the hope that it will be useful,
dnl  but WITHOUT ANY WARRANTY; without even the implied warranty of
dnl  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
dnl  Lesser General Public License for more details.
dnl
dnl  You should have received a copy of the GNU Lesser General Public License
dnl  along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.

include(`../config.m4')


C K6: 10.0 cycles/limb


C mp_limb_t mpn_divexact_by3c (mp_ptr dst, mp_srcptr src, mp_size_t size,
C                              mp_limb_t carry);
C
C Using %esi in (%esi,%ecx,4) or 0(%esi,%ecx,4) addressing modes doesn't
C lead to vector decoding, unlike plain (%esi) does.

defframe(PARAM_CARRY,16)
defframe(PARAM_SIZE, 12)
defframe(PARAM_SRC,   8)
defframe(PARAM_DST,   4)

dnl  multiplicative inverse of 3, modulo 2^32
deflit(INVERSE_3, 0xAAAAAAAB)

	TEXT
	ALIGN(16)

	nop	C code alignment

PROLOGUE(mpn_divexact_by3c)
deflit(`FRAME',0)

	movl	PARAM_SIZE, %ecx
	pushl	%esi		defframe_pushl(SAVE_ESI)

	movl	PARAM_SRC, %esi
	pushl	%edi		defframe_pushl(SAVE_EDI)

	movl	PARAM_DST, %edi
	pushl	%ebx		defframe_pushl(SAVE_EBX)

	movl	PARAM_CARRY, %edx
	leal	(%esi,%ecx,4), %esi

	pushl	%ebp		defframe_pushl(SAVE_EBP)
	movl	$3, %ebp

	leal	0(%edi,%ecx,4), %edi
	negl	%ecx


L(top):
	C eax	scratch, low product
	C ebx	carry limb (0 to 2)
	C ecx	counter, limbs, negative
	C edx	scratch, high product
	C esi	&src[size]
	C edi	&dst[size]
	C ebp	3

	movl	(%esi,%ecx,4), %eax
	subl	%edx, %eax

	sbbl	%ebx, %ebx		C borrow 0 or -1

	imull	$INVERSE_3, %eax, %eax

	movl	%eax, (%edi,%ecx,4)
	addl	$2, %ecx

	mull	%ebp

	subl	%ebx, %edx		C new carry
	loop	L(top)


	movl	SAVE_ESI, %esi
	movl	%edx, %eax

	movl	SAVE_EBX, %ebx

	movl	SAVE_EBP, %ebp

	movl	SAVE_EDI, %edi
	addl	$FRAME, %esp

	ret

EPILOGUE()