divrem_1.asm
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上传日期:2022-08-06
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- dnl Intel Pentium-4 mpn_divrem_1 -- mpn by limb division.
- dnl Copyright 1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation,
- dnl 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 P4: 32 cycles/limb integer part, 30 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 Algorithm:
- C
- C The method and nomenclature follow part 8 of "Division by Invariant
- C Integers using Multiplication" by Granlund and Montgomery, reference in
- C gmp.texi.
- C
- C "m" is written for what is m' in the paper, and "d" for d_norm, which
- C won't cause any confusion since it's only the normalized divisor that's of
- C any use in the code. "b" is written for 2^N, the size of a limb, N being
- C 32 here.
- C
- C The step "sdword dr = n - 2^N*d + (2^N-1-q1) * d" is instead done as
- C "n-d - q1*d". This rearrangement gives the same two-limb answer but lets
- C us have just a psubq on the dependent chain.
- C
- C For reference, the way the k7 code uses "n-(q1+1)*d" would not suit here,
- C detecting an overflow of q1+1 when q1=0xFFFFFFFF would cost too much.
- C
- C Notes:
- C
- C mpn_divrem_1 and mpn_preinv_divrem_1 avoid one division if the src high
- C limb is less than the divisor. mpn_divrem_1c doesn't check for a zero
- C carry, since in normal circumstances that will be a very rare event.
- C
- C The test for skipping a division is branch free (once size>=1 is tested).
- C The store to the destination high limb is 0 when a divide is skipped, or
- C if it's not skipped then a copy of the src high limb is stored. The
- C latter is in case src==dst.
- C
- C There's a small bias towards expecting xsize==0, by having code for
- C xsize==0 in a straight line and xsize!=0 under forward jumps.
- C
- C Enhancements:
- C
- C The loop measures 32 cycles, but the dependent chain would suggest it
- C could be done with 30. Not sure where to start looking for the extras.
- C
- C Alternatives:
- C
- C If the divisor is normalized (high bit set) then a division step can
- C always be skipped, since the high destination limb is always 0 or 1 in
- C that case. It doesn't seem worth checking for this though, since it
- C probably occurs infrequently.
- 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 inverse takes about 80-90 cycles to calculate, but after that the
- dnl multiply is 32 c/l versus division at about 58 c/l.
- dnl
- dnl At 4 limbs the div is a touch faster than the mul (and of course
- dnl simpler), so start the mul from 5 limbs.
- deflit(MUL_THRESHOLD, 5)
- 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)
- dnl re-use parameter space
- define(SAVE_ESI,`PARAM_SIZE')
- define(SAVE_EBP,`PARAM_SRC')
- define(SAVE_EDI,`PARAM_DIVISOR')
- define(SAVE_EBX,`PARAM_DST')
- TEXT
- ALIGN(16)
- PROLOGUE(mpn_preinv_divrem_1)
- deflit(`FRAME',0)
- movl PARAM_SIZE, %ecx
- xorl %edx, %edx C carry if can't skip a div
- movl %esi, SAVE_ESI
- movl PARAM_SRC, %esi
- movl %ebp, SAVE_EBP
- movl PARAM_DIVISOR, %ebp
- movl %edi, SAVE_EDI
- movl PARAM_DST, %edi
- movl -4(%esi,%ecx,4), %eax C src high limb
- movl %ebx, SAVE_EBX
- movl PARAM_XSIZE, %ebx
- movd PARAM_PREINV_INVERSE, %mm4
- movd PARAM_PREINV_SHIFT, %mm7 C l
- cmpl %ebp, %eax C high cmp divisor
- cmovc( %eax, %edx) C high is carry if high<divisor
- movd %edx, %mm0 C carry
- movd %edx, %mm1 C carry
- movl $0, %edx
- movd %ebp, %mm5 C d
- cmovnc( %eax, %edx) C 0 if skip div, src high if not
- C (the latter in case src==dst)
- leal -4(%edi,%ebx,4), %edi C &dst[xsize-1]
- movl %edx, (%edi,%ecx,4) C dst high limb
- sbbl $0, %ecx C skip one division if high<divisor
- movl $32, %eax
- subl PARAM_PREINV_SHIFT, %eax
- psllq %mm7, %mm5 C d normalized
- leal (%edi,%ecx,4), %edi C &dst[xsize+size-1]
- leal -4(%esi,%ecx,4), %esi C &src[size-1]
- movd %eax, %mm6 C 32-l
- jmp L(start_preinv)
- EPILOGUE()
- ALIGN(16)
- PROLOGUE(mpn_divrem_1c)
- deflit(`FRAME',0)
- movl PARAM_CARRY, %edx
- movl PARAM_SIZE, %ecx
- movl %esi, SAVE_ESI
- movl PARAM_SRC, %esi
- movl %ebp, SAVE_EBP
- movl PARAM_DIVISOR, %ebp
- movl %edi, SAVE_EDI
- movl PARAM_DST, %edi
- movl %ebx, SAVE_EBX
- movl PARAM_XSIZE, %ebx
- leal -4(%edi,%ebx,4), %edi C &dst[xsize-1]
- jmp L(start_1c)
- EPILOGUE()
- ALIGN(16)
- PROLOGUE(mpn_divrem_1)
- deflit(`FRAME',0)
- movl PARAM_SIZE, %ecx
- xorl %edx, %edx C initial carry (if can't skip a div)
- movl %esi, SAVE_ESI
- movl PARAM_SRC, %esi
- movl %ebp, SAVE_EBP
- movl PARAM_DIVISOR, %ebp
- movl %edi, SAVE_EDI
- movl PARAM_DST, %edi
- movl %ebx, SAVE_EBX
- movl PARAM_XSIZE, %ebx
- leal -4(%edi,%ebx,4), %edi C &dst[xsize-1]
- orl %ecx, %ecx C size
- jz L(no_skip_div) C if size==0
- movl -4(%esi,%ecx,4), %eax C src high limb
- cmpl %ebp, %eax C high cmp divisor
- cmovnc( %eax, %edx) C 0 if skip div, src high if not
- movl %edx, (%edi,%ecx,4) C dst high limb
- movl $0, %edx
- cmovc( %eax, %edx) C high is carry if high<divisor
- sbbl $0, %ecx C size-1 if high<divisor
- 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
- leal -4(%esi,%ecx,4), %esi C &src[size-1]
- leal (%edi,%ecx,4), %edi C &dst[size+xsize-1]
- cmpl $MUL_THRESHOLD, %eax
- jae L(mul_by_inverse)
- orl %ecx, %ecx
- jz L(divide_no_integer) C if size==0
- L(divide_integer):
- C eax scratch (quotient)
- C ebx xsize
- C ecx counter
- C edx carry
- C esi src, decrementing
- C edi dst, decrementing
- C ebp divisor
- movl (%esi), %eax
- subl $4, %esi
- divl %ebp
- movl %eax, (%edi)
- subl $4, %edi
- subl $1, %ecx
- jnz L(divide_integer)
- L(divide_no_integer):
- orl %ebx, %ebx
- jnz L(divide_fraction) C if xsize!=0
- L(divide_done):
- movl SAVE_ESI, %esi
- movl SAVE_EDI, %edi
- movl SAVE_EBX, %ebx
- movl SAVE_EBP, %ebp
- movl %edx, %eax
- ret
- L(divide_fraction):
- C eax scratch (quotient)
- C ebx counter
- C ecx
- C edx carry
- C esi
- C edi dst, decrementing
- C ebp divisor
- movl $0, %eax
- divl %ebp
- movl %eax, (%edi)
- subl $4, %edi
- subl $1, %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[size-1]
- C edi &dst[size+xsize-1]
- C ebp divisor
- bsrl %ebp, %eax C 31-l
- movd %edx, %mm0 C carry
- movd %edx, %mm1 C carry
- movl %ecx, %edx C size
- movl $31, %ecx
- C
- xorl %eax, %ecx C l = leading zeros on d
- addl $1, %eax
- shll %cl, %ebp C d normalized
- movd %ecx, %mm7 C l
- movl %edx, %ecx C size
- movd %eax, %mm6 C 32-l
- movl $-1, %edx
- movl $-1, %eax
- C
- subl %ebp, %edx C (b-d)-1 so edx:eax = b*(b-d)-1
- divl %ebp C floor (b*(b-d)-1 / d)
- movd %ebp, %mm5 C d
- C
- movd %eax, %mm4 C m
- L(start_preinv):
- C eax inverse
- C ebx xsize
- C ecx size
- C edx
- C esi &src[size-1]
- C edi &dst[size+xsize-1]
- C ebp
- C
- C mm0 carry
- C mm1 carry
- C mm2
- C mm4 m
- C mm5 d
- C mm6 31-l
- C mm7 l
- psllq %mm7, %mm0 C n2 = carry << l, for size==0
- subl $1, %ecx
- jb L(integer_none)
- movd (%esi), %mm0 C src high limb
- punpckldq %mm1, %mm0
- psrlq %mm6, %mm0 C n2 = high (carry:srchigh << l)
- jz L(integer_last)
- C The dependent chain here consists of
- C
- C 2 paddd n1+n2
- C 8 pmuludq m*(n1+n2)
- C 2 paddq n2:nadj + m*(n1+n2)
- C 2 psrlq q1
- C 8 pmuludq d*q1
- C 2 psubq (n-d)-q1*d
- C 2 psrlq high n-(q1+1)*d mask
- C 2 pand d masked
- C 2 paddd n2+d addback
- C --
- C 30
- C
- C But it seems to run at 32 cycles, so presumably there's something else
- C going on.
- ALIGN(16)
- L(integer_top):
- C eax
- C ebx
- C ecx counter, size-1 to 0
- C edx
- C esi src, decrementing
- C edi dst, decrementing
- C
- C mm0 n2
- C mm4 m
- C mm5 d
- C mm6 32-l
- C mm7 l
- ASSERT(b,`C n2<d
- movd %mm0, %eax
- movd %mm5, %edx
- cmpl %edx, %eax')
- movd -4(%esi), %mm1 C next src limbs
- movd (%esi), %mm2
- leal -4(%esi), %esi
- punpckldq %mm2, %mm1
- psrlq %mm6, %mm1 C n10
- movq %mm1, %mm2 C n10
- movq %mm1, %mm3 C n10
- psrad $31, %mm1 C -n1
- pand %mm5, %mm1 C -n1 & d
- paddd %mm2, %mm1 C nadj = n10+(-n1&d), ignore overflow
- psrld $31, %mm2 C n1
- paddd %mm0, %mm2 C n2+n1
- punpckldq %mm0, %mm1 C n2:nadj
- pmuludq %mm4, %mm2 C m*(n2+n1)
- C
- paddq %mm2, %mm1 C n2:nadj + m*(n2+n1)
- pxor %mm2, %mm2 C break dependency, saves 4 cycles
- pcmpeqd %mm2, %mm2 C FF...FF
- psrlq $63, %mm2 C 1
- psrlq $32, %mm1 C q1 = high(n2:nadj + m*(n2+n1))
- paddd %mm1, %mm2 C q1+1
- pmuludq %mm5, %mm1 C q1*d
- punpckldq %mm0, %mm3 C n = n2:n10
- pxor %mm0, %mm0
- psubq %mm5, %mm3 C n - d
- C
- psubq %mm1, %mm3 C n - (q1+1)*d
- por %mm3, %mm0 C copy remainder -> new n2
- psrlq $32, %mm3 C high n - (q1+1)*d, 0 or -1
- ASSERT(be,`C 0 or -1
- movd %mm3, %eax
- addl $1, %eax
- cmpl $1, %eax')
- paddd %mm3, %mm2 C q
- pand %mm5, %mm3 C mask & d
- paddd %mm3, %mm0 C addback if necessary
- movd %mm2, (%edi)
- leal -4(%edi), %edi
- subl $1, %ecx
- ja L(integer_top)
- L(integer_last):
- C eax
- C ebx xsize
- C ecx
- C edx
- C esi &src[0]
- C edi &dst[xsize]
- C
- C mm0 n2
- C mm4 m
- C mm5 d
- C mm6
- C mm7 l
- ASSERT(b,`C n2<d
- movd %mm0, %eax
- movd %mm5, %edx
- cmpl %edx, %eax')
- movd (%esi), %mm1 C src[0]
- psllq %mm7, %mm1 C n10
- movq %mm1, %mm2 C n10
- movq %mm1, %mm3 C n10
- psrad $31, %mm1 C -n1
- pand %mm5, %mm1 C -n1 & d
- paddd %mm2, %mm1 C nadj = n10+(-n1&d), ignore overflow
- psrld $31, %mm2 C n1
- paddd %mm0, %mm2 C n2+n1
- punpckldq %mm0, %mm1 C n2:nadj
- pmuludq %mm4, %mm2 C m*(n2+n1)
- C
- paddq %mm2, %mm1 C n2:nadj + m*(n2+n1)
- pcmpeqd %mm2, %mm2 C FF...FF
- psrlq $63, %mm2 C 1
- psrlq $32, %mm1 C q1 = high(n2:nadj + m*(n2+n1))
- paddd %mm1, %mm2 C q1
- pmuludq %mm5, %mm1 C q1*d
- punpckldq %mm0, %mm3 C n
- psubq %mm5, %mm3 C n - d
- pxor %mm0, %mm0
- C
- psubq %mm1, %mm3 C n - (q1+1)*d
- por %mm3, %mm0 C remainder -> n2
- psrlq $32, %mm3 C high n - (q1+1)*d, 0 or -1
- ASSERT(be,`C 0 or -1
- movd %mm3, %eax
- addl $1, %eax
- cmpl $1, %eax')
- paddd %mm3, %mm2 C q
- pand %mm5, %mm3 C mask & d
- paddd %mm3, %mm0 C addback if necessary
- movd %mm2, (%edi)
- leal -4(%edi), %edi
- L(integer_none):
- C eax
- C ebx xsize
- orl %ebx, %ebx
- jnz L(fraction_some) C if xsize!=0
- L(fraction_done):
- movl SAVE_EBP, %ebp
- psrld %mm7, %mm0 C remainder
- movl SAVE_EDI, %edi
- movd %mm0, %eax
- movl SAVE_ESI, %esi
- movl SAVE_EBX, %ebx
- emms
- ret
- C -----------------------------------------------------------------------------
- C
- L(fraction_some):
- C eax
- C ebx xsize
- C ecx
- C edx
- C esi
- C edi &dst[xsize-1]
- C ebp
- L(fraction_top):
- C eax
- C ebx counter, xsize iterations
- C ecx
- C edx
- C esi src, decrementing
- C edi dst, decrementing
- C
- C mm0 n2
- C mm4 m
- C mm5 d
- C mm6 32-l
- C mm7 l
- ASSERT(b,`C n2<d
- movd %mm0, %eax
- movd %mm5, %edx
- cmpl %edx, %eax')
- movq %mm0, %mm1 C n2
- pmuludq %mm4, %mm0 C m*n2
- pcmpeqd %mm2, %mm2
- psrlq $63, %mm2
- C
- psrlq $32, %mm0 C high(m*n2)
- paddd %mm1, %mm0 C q1 = high(n2:0 + m*n2)
- paddd %mm0, %mm2 C q1+1
- pmuludq %mm5, %mm0 C q1*d
- psllq $32, %mm1 C n = n2:0
- psubq %mm5, %mm1 C n - d
- C
- psubq %mm0, %mm1 C r = n - (q1+1)*d
- pxor %mm0, %mm0
- por %mm1, %mm0 C r -> n2
- psrlq $32, %mm1 C high n - (q1+1)*d, 0 or -1
- ASSERT(be,`C 0 or -1
- movd %mm1, %eax
- addl $1, %eax
- cmpl $1, %eax')
- paddd %mm1, %mm2 C q
- pand %mm5, %mm1 C mask & d
- paddd %mm1, %mm0 C addback if necessary
- movd %mm2, (%edi)
- leal -4(%edi), %edi
- subl $1, %ebx
- jne L(fraction_top)
- jmp L(fraction_done)
- EPILOGUE()