divrem_1.asm
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- dnl Intel Pentium-II mpn_divrem_1 -- mpn by limb division.
- dnl Copyright 1999, 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 P6MMX: 25.0 cycles/limb integer part, 17.5 cycles/limb fraction part.
- C mp_limb_t mpn_divrem_1 (mp_ptr dst, mp_size_t xsize,
- C mp_srcptr src, mp_size_t size,
- C mp_limb_t divisor);
- C mp_limb_t mpn_divrem_1c (mp_ptr dst, mp_size_t xsize,
- C mp_srcptr src, mp_size_t size,
- C mp_limb_t divisor, mp_limb_t carry);
- C mp_limb_t mpn_preinv_divrem_1 (mp_ptr dst, mp_size_t xsize,
- C mp_srcptr src, mp_size_t size,
- C mp_limb_t divisor, mp_limb_t inverse,
- C unsigned shift);
- C
- C This code is a lightly reworked version of mpn/x86/k7/mmx/divrem_1.asm,
- C see that file for some comments. It's possible what's here can be improved.
- dnl MUL_THRESHOLD is the value of xsize+size at which the multiply by
- dnl inverse method is used, rather than plain "divl"s. Minimum value 1.
- dnl
- dnl The different speeds of the integer and fraction parts means that using
- dnl xsize+size isn't quite right. The threshold wants to be a bit higher
- dnl for the integer part and a bit lower for the fraction part. (Or what's
- dnl really wanted is to speed up the integer part!)
- dnl
- dnl The threshold is set to make the integer part right. At 4 limbs the
- dnl div and mul are about the same there, but on the fractional part the
- dnl mul is much faster.
- deflit(MUL_THRESHOLD, 4)
- defframe(PARAM_PREINV_SHIFT, 28) dnl mpn_preinv_divrem_1
- defframe(PARAM_PREINV_INVERSE, 24) dnl mpn_preinv_divrem_1
- defframe(PARAM_CARRY, 24) dnl mpn_divrem_1c
- defframe(PARAM_DIVISOR,20)
- defframe(PARAM_SIZE, 16)
- defframe(PARAM_SRC, 12)
- defframe(PARAM_XSIZE, 8)
- defframe(PARAM_DST, 4)
- defframe(SAVE_EBX, -4)
- defframe(SAVE_ESI, -8)
- defframe(SAVE_EDI, -12)
- defframe(SAVE_EBP, -16)
- defframe(VAR_NORM, -20)
- defframe(VAR_INVERSE, -24)
- defframe(VAR_SRC, -28)
- defframe(VAR_DST, -32)
- defframe(VAR_DST_STOP,-36)
- deflit(STACK_SPACE, 36)
- TEXT
- ALIGN(16)
- PROLOGUE(mpn_preinv_divrem_1)
- deflit(`FRAME',0)
- movl PARAM_XSIZE, %ecx
- subl $STACK_SPACE, %esp FRAME_subl_esp(STACK_SPACE)
- movl %esi, SAVE_ESI
- movl PARAM_SRC, %esi
- movl %ebx, SAVE_EBX
- movl PARAM_SIZE, %ebx
- movl %ebp, SAVE_EBP
- movl PARAM_DIVISOR, %ebp
- movl %edi, SAVE_EDI
- movl PARAM_DST, %edx
- movl -4(%esi,%ebx,4), %eax C src high limb
- xorl %edi, %edi C initial carry (if can't skip a div)
- C
- leal 8(%edx,%ecx,4), %edx C &dst[xsize+2]
- xor %ecx, %ecx
- movl %edx, VAR_DST_STOP C &dst[xsize+2]
- cmpl %ebp, %eax C high cmp divisor
- cmovc( %eax, %edi) C high is carry if high<divisor
- cmovnc( %eax, %ecx) C 0 if skip div, src high if not
- C (the latter in case src==dst)
- movl %ecx, -12(%edx,%ebx,4) C dst high limb
- sbbl $0, %ebx C skip one division if high<divisor
- movl PARAM_PREINV_SHIFT, %ecx
- leal -8(%edx,%ebx,4), %edx C &dst[xsize+size]
- movl $32, %eax
- movl %edx, VAR_DST C &dst[xsize+size]
- shll %cl, %ebp C d normalized
- subl %ecx, %eax
- movl %ecx, VAR_NORM
- movd %eax, %mm7 C rshift
- movl PARAM_PREINV_INVERSE, %eax
- jmp L(start_preinv)
- EPILOGUE()
- ALIGN(16)
- PROLOGUE(mpn_divrem_1c)
- deflit(`FRAME',0)
- movl PARAM_CARRY, %edx
- movl PARAM_SIZE, %ecx
- subl $STACK_SPACE, %esp
- deflit(`FRAME',STACK_SPACE)
- movl %ebx, SAVE_EBX
- movl PARAM_XSIZE, %ebx
- movl %edi, SAVE_EDI
- movl PARAM_DST, %edi
- movl %ebp, SAVE_EBP
- movl PARAM_DIVISOR, %ebp
- movl %esi, SAVE_ESI
- movl PARAM_SRC, %esi
- leal -4(%edi,%ebx,4), %edi
- jmp L(start_1c)
- EPILOGUE()
- C offset 0x31, close enough to aligned
- PROLOGUE(mpn_divrem_1)
- deflit(`FRAME',0)
- movl PARAM_SIZE, %ecx
- movl $0, %edx C initial carry (if can't skip a div)
- subl $STACK_SPACE, %esp
- deflit(`FRAME',STACK_SPACE)
- movl %ebp, SAVE_EBP
- movl PARAM_DIVISOR, %ebp
- movl %ebx, SAVE_EBX
- movl PARAM_XSIZE, %ebx
- movl %esi, SAVE_ESI
- movl PARAM_SRC, %esi
- orl %ecx, %ecx C size
- movl %edi, SAVE_EDI
- movl PARAM_DST, %edi
- leal -4(%edi,%ebx,4), %edi C &dst[xsize-1]
- jz L(no_skip_div) C if size==0
- movl -4(%esi,%ecx,4), %eax C src high limb
- xorl %esi, %esi
- cmpl %ebp, %eax C high cmp divisor
- cmovc( %eax, %edx) C high is carry if high<divisor
- cmovnc( %eax, %esi) C 0 if skip div, src high if not
- C (the latter in case src==dst)
- movl %esi, (%edi,%ecx,4) C dst high limb
- sbbl $0, %ecx C size-1 if high<divisor
- movl PARAM_SRC, %esi C reload
- L(no_skip_div):
- L(start_1c):
- C eax
- C ebx xsize
- C ecx size
- C edx carry
- C esi src
- C edi &dst[xsize-1]
- C ebp divisor
- leal (%ebx,%ecx), %eax C size+xsize
- cmpl $MUL_THRESHOLD, %eax
- jae L(mul_by_inverse)
- orl %ecx, %ecx
- jz L(divide_no_integer)
- L(divide_integer):
- C eax scratch (quotient)
- C ebx xsize
- C ecx counter
- C edx scratch (remainder)
- C esi src
- C edi &dst[xsize-1]
- C ebp divisor
- movl -4(%esi,%ecx,4), %eax
- divl %ebp
- movl %eax, (%edi,%ecx,4)
- decl %ecx
- jnz L(divide_integer)
- L(divide_no_integer):
- movl PARAM_DST, %edi
- orl %ebx, %ebx
- jnz L(divide_fraction)
- L(divide_done):
- movl SAVE_ESI, %esi
- movl SAVE_EDI, %edi
- movl SAVE_EBX, %ebx
- movl %edx, %eax
- movl SAVE_EBP, %ebp
- addl $STACK_SPACE, %esp
- ret
- L(divide_fraction):
- C eax scratch (quotient)
- C ebx counter
- C ecx
- C edx scratch (remainder)
- C esi
- C edi dst
- C ebp divisor
- movl $0, %eax
- divl %ebp
- movl %eax, -4(%edi,%ebx,4)
- decl %ebx
- jnz L(divide_fraction)
- jmp L(divide_done)
- C -----------------------------------------------------------------------------
- L(mul_by_inverse):
- C eax
- C ebx xsize
- C ecx size
- C edx carry
- C esi src
- C edi &dst[xsize-1]
- C ebp divisor
- leal 12(%edi), %ebx C &dst[xsize+2], loop dst stop
- movl %ebx, VAR_DST_STOP
- leal 4(%edi,%ecx,4), %edi C &dst[xsize+size]
- movl %edi, VAR_DST
- movl %ecx, %ebx C size
- bsrl %ebp, %ecx C 31-l
- movl %edx, %edi C carry
- leal 1(%ecx), %eax C 32-l
- xorl $31, %ecx C l
- movl %ecx, VAR_NORM
- movl $-1, %edx
- shll %cl, %ebp C d normalized
- movd %eax, %mm7
- movl $-1, %eax
- subl %ebp, %edx C (b-d)-1 giving edx:eax = b*(b-d)-1
- divl %ebp C floor (b*(b-d)-1) / d
- L(start_preinv):
- C eax inverse
- C ebx size
- C ecx shift
- C edx
- C esi src
- C edi carry
- C ebp divisor
- C
- C mm7 rshift
- movl %eax, VAR_INVERSE
- orl %ebx, %ebx C size
- leal -12(%esi,%ebx,4), %eax C &src[size-3]
- movl %eax, VAR_SRC
- jz L(start_zero)
- movl 8(%eax), %esi C src high limb
- cmpl $1, %ebx
- jz L(start_one)
- L(start_two_or_more):
- movl 4(%eax), %edx C src second highest limb
- shldl( %cl, %esi, %edi) C n2 = carry,high << l
- shldl( %cl, %edx, %esi) C n10 = high,second << l
- cmpl $2, %ebx
- je L(integer_two_left)
- jmp L(integer_top)
- L(start_one):
- shldl( %cl, %esi, %edi) C n2 = carry,high << l
- shll %cl, %esi C n10 = high << l
- jmp L(integer_one_left)
- L(start_zero):
- C Can be here with xsize==0 if mpn_preinv_divrem_1 had size==1 and
- C skipped a division.
- shll %cl, %edi C n2 = carry << l
- movl %edi, %eax C return value for zero_done
- cmpl $0, PARAM_XSIZE
- je L(zero_done)
- jmp L(fraction_some)
- C -----------------------------------------------------------------------------
- C
- C This loop runs at about 25 cycles, which is probably sub-optimal, and
- C certainly more than the dependent chain would suggest. A better loop, or
- C a better rough analysis of what's possible, would be welcomed.
- C
- C In the current implementation, the following successively dependent
- C micro-ops seem to exist.
- C
- C uops
- C n2+n1 1 (addl)
- C mul 5
- C q1+1 3 (addl/adcl)
- C mul 5
- C sub 3 (subl/sbbl)
- C addback 2 (cmov)
- C ---
- C 19
- C
- C Lack of registers hinders explicit scheduling and it might be that the
- C normal out of order execution isn't able to hide enough under the mul
- C latencies.
- C
- C Using sarl/negl to pick out n1 for the n2+n1 stage is a touch faster than
- C cmov (and takes one uop off the dependent chain). A sarl/andl/addl
- C combination was tried for the addback (despite the fact it would lengthen
- C the dependent chain) but found to be no faster.
- ALIGN(16)
- L(integer_top):
- C eax scratch
- C ebx scratch (nadj, q1)
- C ecx scratch (src, dst)
- C edx scratch
- C esi n10
- C edi n2
- C ebp d
- C
- C mm0 scratch (src qword)
- C mm7 rshift for normalization
- movl %esi, %eax
- movl %ebp, %ebx
- sarl $31, %eax C -n1
- movl VAR_SRC, %ecx
- andl %eax, %ebx C -n1 & d
- negl %eax C n1
- addl %esi, %ebx C nadj = n10 + (-n1 & d), ignoring overflow
- addl %edi, %eax C n2+n1
- movq (%ecx), %mm0 C next src limb and the one below it
- mull VAR_INVERSE C m*(n2+n1)
- subl $4, %ecx
- movl %ecx, VAR_SRC
- C
- C
- addl %ebx, %eax C m*(n2+n1) + nadj, low giving carry flag
- movl %ebp, %eax C d
- leal 1(%edi), %ebx C n2+1
- adcl %edx, %ebx C 1 + high(n2<<32 + m*(n2+n1) + nadj) = q1+1
- jz L(q1_ff)
- mull %ebx C (q1+1)*d
- movl VAR_DST, %ecx
- psrlq %mm7, %mm0
- C
- C
- C
- subl %eax, %esi
- movl VAR_DST_STOP, %eax
- sbbl %edx, %edi C n - (q1+1)*d
- movl %esi, %edi C remainder -> n2
- leal (%ebp,%esi), %edx
- cmovc( %edx, %edi) C n - q1*d if underflow from using q1+1
- movd %mm0, %esi
- sbbl $0, %ebx C q
- subl $4, %ecx
- movl %ebx, (%ecx)
- cmpl %eax, %ecx
- movl %ecx, VAR_DST
- jne L(integer_top)
- L(integer_loop_done):
- C -----------------------------------------------------------------------------
- C
- C Here, and in integer_one_left below, an sbbl $0 is used rather than a jz
- C q1_ff special case. This make the code a bit smaller and simpler, and
- C costs only 2 cycles (each).
- L(integer_two_left):
- C eax scratch
- C ebx scratch (nadj, q1)
- C ecx scratch (src, dst)
- C edx scratch
- C esi n10
- C edi n2
- C ebp divisor
- C
- C mm7 rshift
- movl %esi, %eax
- movl %ebp, %ebx
- sarl $31, %eax C -n1
- movl PARAM_SRC, %ecx
- andl %eax, %ebx C -n1 & d
- negl %eax C n1
- addl %esi, %ebx C nadj = n10 + (-n1 & d), ignoring overflow
- addl %edi, %eax C n2+n1
- mull VAR_INVERSE C m*(n2+n1)
- movd (%ecx), %mm0 C src low limb
- movl VAR_DST_STOP, %ecx
- C
- C
- addl %ebx, %eax C m*(n2+n1) + nadj, low giving carry flag
- leal 1(%edi), %ebx C n2+1
- movl %ebp, %eax C d
- adcl %edx, %ebx C 1 + high(n2<<32 + m*(n2+n1) + nadj) = q1+1
- sbbl $0, %ebx
- mull %ebx C (q1+1)*d
- psllq $32, %mm0
- psrlq %mm7, %mm0
- C
- C
- subl %eax, %esi
- sbbl %edx, %edi C n - (q1+1)*d
- movl %esi, %edi C remainder -> n2
- leal (%ebp,%esi), %edx
- cmovc( %edx, %edi) C n - q1*d if underflow from using q1+1
- movd %mm0, %esi
- sbbl $0, %ebx C q
- movl %ebx, -4(%ecx)
- C -----------------------------------------------------------------------------
- L(integer_one_left):
- C eax scratch
- C ebx scratch (nadj, q1)
- C ecx scratch (dst)
- C edx scratch
- C esi n10
- C edi n2
- C ebp divisor
- C
- C mm7 rshift
- movl %esi, %eax
- movl %ebp, %ebx
- sarl $31, %eax C -n1
- movl VAR_DST_STOP, %ecx
- andl %eax, %ebx C -n1 & d
- negl %eax C n1
- addl %esi, %ebx C nadj = n10 + (-n1 & d), ignoring overflow
- addl %edi, %eax C n2+n1
- mull VAR_INVERSE C m*(n2+n1)
- C
- C
- C
- addl %ebx, %eax C m*(n2+n1) + nadj, low giving carry flag
- leal 1(%edi), %ebx C n2+1
- movl %ebp, %eax C d
- C
- adcl %edx, %ebx C 1 + high(n2<<32 + m*(n2+n1) + nadj) = q1+1
- sbbl $0, %ebx C q1 if q1+1 overflowed
- mull %ebx
- C
- C
- C
- C
- subl %eax, %esi
- movl PARAM_XSIZE, %eax
- sbbl %edx, %edi C n - (q1+1)*d
- movl %esi, %edi C remainder -> n2
- leal (%ebp,%esi), %edx
- cmovc( %edx, %edi) C n - q1*d if underflow from using q1+1
- sbbl $0, %ebx C q
- movl %ebx, -8(%ecx)
- subl $8, %ecx
- orl %eax, %eax C xsize
- jnz L(fraction_some)
- movl %edi, %eax
- L(fraction_done):
- movl VAR_NORM, %ecx
- L(zero_done):
- movl SAVE_EBP, %ebp
- movl SAVE_EDI, %edi
- movl SAVE_ESI, %esi
- movl SAVE_EBX, %ebx
- addl $STACK_SPACE, %esp
- shrl %cl, %eax
- emms
- ret
- C -----------------------------------------------------------------------------
- C
- C Special case for q1=0xFFFFFFFF, giving q=0xFFFFFFFF meaning the low dword
- C of q*d is simply -d and the remainder n-q*d = n10+d
- L(q1_ff):
- C eax (divisor)
- C ebx (q1+1 == 0)
- C ecx
- C edx
- C esi n10
- C edi n2
- C ebp divisor
- movl VAR_DST, %ecx
- movl VAR_DST_STOP, %edx
- subl $4, %ecx
- movl %ecx, VAR_DST
- psrlq %mm7, %mm0
- leal (%ebp,%esi), %edi C n-q*d remainder -> next n2
- movl $-1, (%ecx)
- movd %mm0, %esi C next n10
- cmpl %ecx, %edx
- jne L(integer_top)
- jmp L(integer_loop_done)
- C -----------------------------------------------------------------------------
- C
- C In the current implementation, the following successively dependent
- C micro-ops seem to exist.
- C
- C uops
- C mul 5
- C q1+1 1 (addl)
- C mul 5
- C sub 3 (negl/sbbl)
- C addback 2 (cmov)
- C ---
- C 16
- C
- C The loop in fact runs at about 17.5 cycles. Using a sarl/andl/addl for
- C the addback was found to be a touch slower.
- ALIGN(16)
- L(fraction_some):
- C eax
- C ebx
- C ecx
- C edx
- C esi
- C edi carry
- C ebp divisor
- movl PARAM_DST, %esi
- movl VAR_DST_STOP, %ecx C &dst[xsize+2]
- movl %edi, %eax
- subl $8, %ecx C &dst[xsize]
- ALIGN(16)
- L(fraction_top):
- C eax n2, then scratch
- C ebx scratch (nadj, q1)
- C ecx dst, decrementing
- C edx scratch
- C esi dst stop point
- C edi n2
- C ebp divisor
- mull VAR_INVERSE C m*n2
- movl %ebp, %eax C d
- subl $4, %ecx C dst
- leal 1(%edi), %ebx
- C
- C
- C
- addl %edx, %ebx C 1 + high(n2<<32 + m*n2) = q1+1
- mull %ebx C (q1+1)*d
- C
- C
- C
- C
- negl %eax C low of n - (q1+1)*d
- sbbl %edx, %edi C high of n - (q1+1)*d, caring only about carry
- leal (%ebp,%eax), %edx
- cmovc( %edx, %eax) C n - q1*d if underflow from using q1+1
- sbbl $0, %ebx C q
- movl %eax, %edi C remainder->n2
- cmpl %esi, %ecx
- movl %ebx, (%ecx) C previous q
- jne L(fraction_top)
- jmp L(fraction_done)
- EPILOGUE()