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dnl Intel Pentium mpn_divexact_1 -- mpn by limb exact division.
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 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 divisor
C odd even
C P54: 24.5 30.5 cycles/limb
C P55: 23.0 28.0
C void mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size,
C mp_limb_t divisor);
C
C Plain divl is used for small sizes, since the inverse takes a while to
C setup. Multiplying works out faster for size>=3 when the divisor is odd,
C or size>=4 when the divisor is even. Actually on P55 size==2 for odd or
C size==3 for even are about the same speed for both divl or mul, but the
C former is used since it will use up less code cache.
C
C The P55 speeds noted above, 23 cycles odd or 28 cycles even, are as
C expected. On P54 in the even case the shrdl pairing nonsense (see
C mpn/x86/pentium/README) costs 1 cycle, but it's not clear why there's a
C further 1.5 slowdown for both odd and even.
defframe(PARAM_DIVISOR,16)
defframe(PARAM_SIZE, 12)
defframe(PARAM_SRC, 8)
defframe(PARAM_DST, 4)
dnl re-use parameter space
define(VAR_INVERSE,`PARAM_DST')
TEXT
ALIGN(32)
PROLOGUE(mpn_divexact_1)
deflit(`FRAME',0)
movl PARAM_DIVISOR, %eax
movl PARAM_SIZE, %ecx
pushl %esi FRAME_pushl()
push %edi FRAME_pushl()
movl PARAM_SRC, %esi
andl $1, %eax
movl PARAM_DST, %edi
addl %ecx, %eax C size if even, size+1 if odd
cmpl $4, %eax
jae L(mul_by_inverse)
xorl %edx, %edx
L(div_top):
movl -4(%esi,%ecx,4), %eax
divl PARAM_DIVISOR
movl %eax, -4(%edi,%ecx,4)
decl %ecx
jnz L(div_top)
popl %edi
popl %esi
ret
L(mul_by_inverse):
movl PARAM_DIVISOR, %eax
movl $-1, %ecx
L(strip_twos):
ASSERT(nz, `orl %eax, %eax')
shrl %eax
incl %ecx C shift count
jnc L(strip_twos)
leal 1(%eax,%eax), %edx C d
andl $127, %eax C d/2, 7 bits
pushl %ebx FRAME_pushl()
pushl %ebp FRAME_pushl()
ifdef(`PIC',`
call L(here)
L(here):
popl %ebp C eip
addl $_GLOBAL_OFFSET_TABLE_+[.-L(here)], %ebp
C AGI
movl modlimb_invert_table@GOT(%ebp), %ebp
C AGI
movzbl (%eax,%ebp), %eax
',`
dnl non-PIC
movzbl modlimb_invert_table(%eax), %eax C inv 8 bits
')
movl %eax, %ebp C inv
addl %eax, %eax C 2*inv
imull %ebp, %ebp C inv*inv
imull %edx, %ebp C inv*inv*d
subl %ebp, %eax C inv = 2*inv - inv*inv*d
movl PARAM_SIZE, %ebx
movl %eax, %ebp
addl %eax, %eax C 2*inv
imull %ebp, %ebp C inv*inv
imull %edx, %ebp C inv*inv*d
subl %ebp, %eax C inv = 2*inv - inv*inv*d
movl %edx, PARAM_DIVISOR C d without twos
leal (%esi,%ebx,4), %esi C src end
leal (%edi,%ebx,4), %edi C dst end
negl %ebx C -size
ASSERT(e,` C expect d*inv == 1 mod 2^BITS_PER_MP_LIMB
pushl %eax FRAME_pushl()
imull PARAM_DIVISOR, %eax
cmpl $1, %eax
popl %eax FRAME_popl()')
movl %eax, VAR_INVERSE
xorl %ebp, %ebp C initial carry bit
movl (%esi,%ebx,4), %eax C src low limb
orl %ecx, %ecx C shift
movl 4(%esi,%ebx,4), %edx C src second limb (for even)
jz L(odd_entry)
shrdl( %cl, %edx, %eax)
incl %ebx
jmp L(even_entry)
ALIGN(8)
L(odd_top):
C eax scratch
C ebx counter, limbs, negative
C ecx
C edx
C esi src end
C edi dst end
C ebp carry bit, 0 or -1
mull PARAM_DIVISOR
movl (%esi,%ebx,4), %eax
subl %ebp, %edx
subl %edx, %eax
sbbl %ebp, %ebp
L(odd_entry):
imull VAR_INVERSE, %eax
movl %eax, (%edi,%ebx,4)
incl %ebx
jnz L(odd_top)
popl %ebp
popl %ebx
popl %edi
popl %esi
ret
L(even_top):
C eax scratch
C ebx counter, limbs, negative
C ecx twos
C edx
C esi src end
C edi dst end
C ebp carry bit, 0 or -1
mull PARAM_DIVISOR
subl %ebp, %edx C carry bit
movl -4(%esi,%ebx,4), %eax C src limb
movl (%esi,%ebx,4), %ebp C and one above it
shrdl( %cl, %ebp, %eax)
subl %edx, %eax C carry limb
sbbl %ebp, %ebp
L(even_entry):
imull VAR_INVERSE, %eax
movl %eax, -4(%edi,%ebx,4)
incl %ebx
jnz L(even_top)
mull PARAM_DIVISOR
movl -4(%esi), %eax C src high limb
subl %ebp, %edx
shrl %cl, %eax
subl %edx, %eax C no carry if division is exact
imull VAR_INVERSE, %eax
movl %eax, -4(%edi) C dst high limb
nop C protect against cache bank clash
popl %ebp
popl %ebx
popl %edi
popl %esi
ret
EPILOGUE()
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