mul_1.asm
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上传日期:2022-08-06
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- dnl Intel Pentium MMX mpn_mul_1 -- mpn by limb multiplication.
- 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 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 cycles/limb
- C P5: 12.0 for 32-bit multiplier
- C 7.0 for 16-bit multiplier
- C mp_limb_t mpn_mul_1 (mp_ptr dst, mp_srcptr src, mp_size_t size,
- C mp_limb_t multiplier);
- C
- C When the multiplier is 16 bits some special case MMX code is used. Small
- C multipliers might arise reasonably often from mpz_mul_ui etc. If the size
- C is odd there's roughly a 5 cycle penalty, so times for say size==7 and
- C size==8 end up being quite close. If src isn't aligned to an 8 byte
- C boundary then one limb is processed separately with roughly a 5 cycle
- C penalty, so in that case it's say size==8 and size==9 which are close.
- C
- C Alternatives:
- C
- C MMX is not believed to be of any use for 32-bit multipliers, since for
- C instance the current method would just have to be more or less duplicated
- C for the high and low halves of the multiplier, and would probably
- C therefore run at about 14 cycles, which is slower than the plain integer
- C at 12.
- C
- C Adding the high and low MMX products using integer code seems best. An
- C attempt at using paddd and carry bit propagation with pcmpgtd didn't give
- C any joy. Perhaps something could be done keeping the values signed and
- C thereby avoiding adjustments to make pcmpgtd into an unsigned compare, or
- C perhaps not.
- C
- C Future:
- C
- C An mpn_mul_1c entrypoint would need a double carry out of the low result
- C limb in the 16-bit code, unless it could be assumed the carry fits in 16
- C bits, possibly as carry<multiplier, this being true of a big calculation
- C done piece by piece. But let's worry about that if/when mul_1c is
- C actually used.
- defframe(PARAM_MULTIPLIER,16)
- defframe(PARAM_SIZE, 12)
- defframe(PARAM_SRC, 8)
- defframe(PARAM_DST, 4)
- TEXT
- ALIGN(8)
- PROLOGUE(mpn_mul_1)
- deflit(`FRAME',0)
- movl PARAM_SIZE, %ecx
- movl PARAM_SRC, %edx
- cmpl $1, %ecx
- jne L(two_or_more)
- C one limb only
- movl PARAM_MULTIPLIER, %eax
- movl PARAM_DST, %ecx
- mull (%edx)
- movl %eax, (%ecx)
- movl %edx, %eax
- ret
- L(two_or_more):
- C eax size
- C ebx
- C ecx carry
- C edx
- C esi src
- C edi
- C ebp
- pushl %esi FRAME_pushl()
- pushl %edi FRAME_pushl()
- movl %edx, %esi C src
- movl PARAM_DST, %edi
- movl PARAM_MULTIPLIER, %eax
- pushl %ebx FRAME_pushl()
- leal (%esi,%ecx,4), %esi C src end
- leal (%edi,%ecx,4), %edi C dst end
- negl %ecx C -size
- pushl %ebp FRAME_pushl()
- cmpl $65536, %eax
- jb L(small)
- L(big):
- xorl %ebx, %ebx C carry limb
- sarl %ecx C -size/2
- jnc L(top) C with carry flag clear
- C size was odd, process one limb separately
- mull 4(%esi,%ecx,8) C m * src[0]
- movl %eax, 4(%edi,%ecx,8)
- incl %ecx
- orl %edx, %ebx C carry limb, and clear carry flag
- L(top):
- C eax
- C ebx carry
- C ecx counter, negative
- C edx
- C esi src end
- C edi dst end
- C ebp (scratch carry)
- adcl $0, %ebx
- movl (%esi,%ecx,8), %eax
- mull PARAM_MULTIPLIER
- movl %edx, %ebp
- addl %eax, %ebx
- adcl $0, %ebp
- movl 4(%esi,%ecx,8), %eax
- mull PARAM_MULTIPLIER
- movl %ebx, (%edi,%ecx,8)
- addl %ebp, %eax
- movl %eax, 4(%edi,%ecx,8)
- incl %ecx
- movl %edx, %ebx
- jnz L(top)
- adcl $0, %ebx
- popl %ebp
- movl %ebx, %eax
- popl %ebx
- popl %edi
- popl %esi
- ret
- L(small):
- C Special case for 16-bit multiplier.
- C
- C eax multiplier
- C ebx
- C ecx -size
- C edx src
- C esi src end
- C edi dst end
- C ebp multiplier
- C size<3 not supported here. At size==3 we're already a couple of
- C cycles faster, so there's no threshold as such, just use the MMX
- C as soon as possible.
- cmpl $-3, %ecx
- ja L(big)
- movd %eax, %mm7 C m
- pxor %mm6, %mm6 C initial carry word
- punpcklwd %mm7, %mm7 C m replicated 2 times
- addl $2, %ecx C -size+2
- punpckldq %mm7, %mm7 C m replicated 4 times
- andl $4, %edx C test alignment, clear carry flag
- movq %mm7, %mm0 C m
- jz L(small_entry)
- C Source is unaligned, process one limb separately.
- C
- C Plain integer code is used here, since it's smaller and is about
- C the same 13 cycles as an mmx block would be.
- C
- C An "addl $1,%ecx" doesn't clear the carry flag when size==3, hence
- C the use of separate incl and orl.
- mull -8(%esi,%ecx,4) C m * src[0]
- movl %eax, -8(%edi,%ecx,4) C dst[0]
- incl %ecx C one limb processed
- movd %edx, %mm6 C initial carry
- orl %eax, %eax C clear carry flag
- jmp L(small_entry)
- C The scheduling here is quite tricky, since so many instructions have
- C pairing restrictions. In particular the js won't pair with a movd, and
- C can't be paired with an adc since it wants flags from the inc, so
- C instructions are rotated to the top of the loop to find somewhere useful
- C for it.
- C
- C Trouble has been taken to avoid overlapping successive loop iterations,
- C since that would greatly increase the size of the startup and finishup
- C code. Actually there's probably not much advantage to be had from
- C overlapping anyway, since the difficulties are mostly with pairing, not
- C with latencies as such.
- C
- C In the comments x represents the src data and m the multiplier (16
- C bits, but replicated 4 times).
- C
- C The m signs calculated in %mm3 are a loop invariant and could be held in
- C say %mm5, but that would save only one instruction and hence be no faster.
- L(small_top):
- C eax l.low, then l.high
- C ebx (h.low)
- C ecx counter, -size+2 to 0 or 1
- C edx (h.high)
- C esi &src[size]
- C edi &dst[size]
- C ebp
- C
- C %mm0 (high products)
- C %mm1 (low products)
- C %mm2 (adjust for m using x signs)
- C %mm3 (adjust for x using m signs)
- C %mm4
- C %mm5
- C %mm6 h.low, then carry
- C %mm7 m replicated 4 times
- movd %mm6, %ebx C h.low
- psrlq $32, %mm1 C l.high
- movd %mm0, %edx C h.high
- movq %mm0, %mm6 C new c
- adcl %eax, %ebx
- incl %ecx
- movd %mm1, %eax C l.high
- movq %mm7, %mm0
- adcl %eax, %edx
- movl %ebx, -16(%edi,%ecx,4)
- movl %edx, -12(%edi,%ecx,4)
- psrlq $32, %mm6 C c
- L(small_entry):
- pmulhw -8(%esi,%ecx,4), %mm0 C h = (x*m).high
- movq %mm7, %mm1
- pmullw -8(%esi,%ecx,4), %mm1 C l = (x*m).low
- movq %mm7, %mm3
- movq -8(%esi,%ecx,4), %mm2 C x
- psraw $15, %mm3 C m signs
- pand -8(%esi,%ecx,4), %mm3 C x selected by m signs
- psraw $15, %mm2 C x signs
- paddw %mm3, %mm0 C add x to h if m neg
- pand %mm7, %mm2 C m selected by x signs
- paddw %mm2, %mm0 C add m to h if x neg
- incl %ecx
- movd %mm1, %eax C l.low
- punpcklwd %mm0, %mm6 C c + h.low << 16
- psrlq $16, %mm0 C h.high
- js L(small_top)
- movd %mm6, %ebx C h.low
- psrlq $32, %mm1 C l.high
- adcl %eax, %ebx
- popl %ebp FRAME_popl()
- movd %mm0, %edx C h.high
- psrlq $32, %mm0 C l.high
- movd %mm1, %eax C l.high
- adcl %eax, %edx
- movl %ebx, -12(%edi,%ecx,4)
- movd %mm0, %eax C c
- adcl $0, %eax
- movl %edx, -8(%edi,%ecx,4)
- orl %ecx, %ecx
- jnz L(small_done) C final %ecx==1 means even, ==0 odd
- C Size odd, one extra limb to process.
- C Plain integer code is used here, since it's smaller and is about
- C the same speed as another mmx block would be.
- movl %eax, %ecx
- movl PARAM_MULTIPLIER, %eax
- mull -4(%esi)
- addl %ecx, %eax
- adcl $0, %edx
- movl %eax, -4(%edi)
- movl %edx, %eax
- L(small_done):
- popl %ebx
- popl %edi
- popl %esi
- emms
- ret
- EPILOGUE()