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dnl x86 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 2.1 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
dnl License along with the GNU MP Library; see the file COPYING.LIB. If
dnl not, write to the Free Software Foundation, Inc., 51 Franklin Street,
dnl Fifth Floor, Boston, MA 02110-1301, USA.
include(`../config.m4')
C cycles/limb
C P54 18.0
C P55 17.0
C P6 14.0
C K6 14.0
C K7 10.0
C P4 24.0
C mp_limb_t mpn_divexact_by3c (mp_ptr dst, mp_srcptr src, mp_size_t size,
C mp_limb_t carry);
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)
dnl ceil(b/3) and ceil(b*2/3) where b=2^32
deflit(ONE_THIRD_CEIL, 0x55555556)
deflit(TWO_THIRDS_CEIL, 0xAAAAAAAB)
TEXT
ALIGN(8)
PROLOGUE(mpn_divexact_by3c)
deflit(`FRAME',0)
movl PARAM_SRC, %ecx
pushl %ebp FRAME_pushl()
movl PARAM_SIZE, %ebp
pushl %edi FRAME_pushl()
movl PARAM_DST, %edi
pushl %esi FRAME_pushl()
movl $INVERSE_3, %esi
pushl %ebx FRAME_pushl()
leal (%ecx,%ebp,4), %ecx
movl PARAM_CARRY, %ebx
leal (%edi,%ebp,4), %edi
negl %ebp
ALIGN(8)
L(top):
C eax scratch, low product
C ebx carry limb (0 to 3)
C ecx &src[size]
C edx scratch, high product
C esi multiplier
C edi &dst[size]
C ebp counter, limbs, negative
movl (%ecx,%ebp,4), %eax
subl %ebx, %eax
setc %bl
imull %esi
cmpl $ONE_THIRD_CEIL, %eax
movl %eax, (%edi,%ebp,4)
sbbl $-1, %ebx C +1 if eax>=ceil(b/3)
cmpl $TWO_THIRDS_CEIL, %eax
sbbl $-1, %ebx C +1 if eax>=ceil(b*2/3)
incl %ebp
jnz L(top)
movl %ebx, %eax
popl %ebx
popl %esi
popl %edi
popl %ebp
ret
EPILOGUE()
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