dnl  Intel Pentium-4 mpn_divexact_by3 -- mpn exact division by 3.

dnl  Copyright 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 Library General Public License as
dnl  published by the Free Software Foundation; either version 2 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  Library General Public License for more details.
dnl 
dnl  You should have received a copy of the GNU Library General Public
dnl  License along with the GNU MP Library; see the file COPYING.LIB.  If
dnl  not, write to the Free Software Foundation, Inc., 59 Temple Place -
dnl  Suite 330, Boston, MA 02111-1307, USA.

include(`../config.m4')


C P4: 18.0 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 The dependent chain in the loop is as follows, and this is what the code
C measures.
C
C	psubq     (src-cbit) - climb	2
C	pmuludq   s*inverse		8
C	pand      mask q		2
C	psllq     2*q			2
C	paddq     q+2*q			2
C	psrlq     high(3*q)		2
C				       --
C				       18
C
C Perhaps the s*inverse can be taken off the dependent chain as described in
C mpn/generic/diveby3.c, with a modified 3*q calculation that can give
C high(3*q)*inv too.


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

	RODATA
C multiplicative inverse of 3, modulo 2^32
	ALIGN(4)
L(inverse):
	.long	0xAAAAAAAB

	TEXT
	ALIGN(16)

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

	movl	PARAM_SRC, %eax
	pxor	%mm0, %mm0

	movd	PARAM_CARRY, %mm1
	pcmpeqd	%mm6, %mm6

	movd	L(inverse), %mm7

	movl	PARAM_DST, %edx
	psrlq	$32, %mm6		C 0x00000000FFFFFFFF

	movl	PARAM_SIZE, %ecx

L(top):
	C eax	src, incrementing
	C ebx
	C ecx	counter, limbs, decrementing
	C edx	dst, incrementing
	C
	C mm0	carry bit
	C mm1	carry limb
	C mm6	0x00000000FFFFFFFF
	C mm7	inverse

	movd	(%eax), %mm2
	addl	$4, %eax

	psubq	%mm0, %mm2		C src - cbit

	psubq	%mm1, %mm2		C src - cbit - climb
	movq	%mm2, %mm0
	psrlq	$63, %mm0		C new cbit

	pmuludq	%mm7, %mm2		C s*inverse
	movd	%mm2, (%edx)		C q
	addl	$4, %edx

	movq	%mm6, %mm1

	pand	%mm2, %mm1

	pand	%mm6, %mm2

	psllq	$1, %mm1

	C

	paddq	%mm2, %mm1

	C

	psrlq	$32, %mm1

	subl	$1, %ecx
	jnz	L(top)


	paddd	%mm1, %mm0
	movd	%mm0, %eax
	emms
	ret

EPILOGUE()
