rshift.asm
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上传日期:2022-08-06
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- dnl Intel P5 mpn_rshift -- mpn right shift.
- dnl Copyright 2000, 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 P5: 1.75 cycles/limb.
- C mp_limb_t mpn_rshift (mp_ptr dst, mp_srcptr src, mp_size_t size,
- C unsigned shift);
- C
- C Shift src,size right by shift many bits and store the result in dst,size.
- C Zeros are shifted in at the left. Return the bits shifted out at the
- C right.
- C
- C It takes 6 mmx instructions to process 2 limbs, making 1.5 cycles/limb,
- C and with a 4 limb loop and 1 cycle of loop overhead the total is 1.75 c/l.
- C
- C Full speed depends on source and destination being aligned. Unaligned mmx
- C loads and stores on P5 don't pair and have a 2 cycle penalty. Some hairy
- C setups and finish-ups are done to ensure alignment for the loop.
- C
- C MMX shifts work out a bit faster even for the simple loop.
- defframe(PARAM_SHIFT,16)
- defframe(PARAM_SIZE, 12)
- defframe(PARAM_SRC, 8)
- defframe(PARAM_DST, 4)
- deflit(`FRAME',0)
- dnl Minimum 5, because the unrolled loop can't handle less.
- deflit(UNROLL_THRESHOLD, 5)
- TEXT
- ALIGN(8)
- PROLOGUE(mpn_rshift)
- pushl %ebx
- pushl %edi
- deflit(`FRAME',8)
- movl PARAM_SIZE, %eax
- movl PARAM_DST, %edx
- movl PARAM_SRC, %ebx
- movl PARAM_SHIFT, %ecx
- cmp $UNROLL_THRESHOLD, %eax
- jae L(unroll)
- decl %eax
- movl (%ebx), %edi C src low limb
- jnz L(simple)
- shrdl( %cl, %edi, %eax) C eax was decremented to zero
- shrl %cl, %edi
- movl %edi, (%edx) C dst low limb
- popl %edi C risk of data cache bank clash
- popl %ebx
- ret
- C -----------------------------------------------------------------------------
- ALIGN(8)
- L(simple):
- C eax size-1
- C ebx src
- C ecx shift
- C edx dst
- C esi
- C edi
- C ebp
- deflit(`FRAME',8)
- movd (%ebx), %mm5 C src[0]
- leal (%ebx,%eax,4), %ebx C &src[size-1]
- movd %ecx, %mm6 C rshift
- leal -4(%edx,%eax,4), %edx C &dst[size-2]
- psllq $32, %mm5
- negl %eax
- C This loop is 5 or 8 cycles, with every second load unaligned and a wasted
- C cycle waiting for the mm0 result to be ready. For comparison a shrdl is 4
- C cycles and would be 8 in a simple loop. Using mmx helps the return value
- C and last limb calculations too.
- L(simple_top):
- C eax counter, limbs, negative
- C ebx &src[size-1]
- C ecx return value
- C edx &dst[size-2]
- C
- C mm0 scratch
- C mm5 return value
- C mm6 shift
- movq (%ebx,%eax,4), %mm0
- incl %eax
- psrlq %mm6, %mm0
- movd %mm0, (%edx,%eax,4)
- jnz L(simple_top)
- movd (%ebx), %mm0
- psrlq %mm6, %mm5 C return value
- psrlq %mm6, %mm0
- popl %edi
- movd %mm5, %eax
- popl %ebx
- movd %mm0, 4(%edx)
- emms
- ret
- C -----------------------------------------------------------------------------
- ALIGN(8)
- L(unroll):
- C eax size
- C ebx src
- C ecx shift
- C edx dst
- C esi
- C edi
- C ebp
- deflit(`FRAME',8)
- movd (%ebx), %mm5 C src[0]
- movl $4, %edi
- movd %ecx, %mm6 C rshift
- testl %edi, %ebx
- psllq $32, %mm5
- jz L(start_src_aligned)
- C src isn't aligned, process low limb separately (marked xxx) and
- C step src and dst by one limb, making src aligned.
- C
- C source ebx
- C --+-------+-------+-------+
- C | xxx |
- C --+-------+-------+-------+
- C 4mod8 0mod8 4mod8
- C
- C dest edx
- C --+-------+-------+
- C | | xxx |
- C --+-------+-------+
- movq (%ebx), %mm0 C unaligned load
- psrlq %mm6, %mm0
- addl $4, %ebx
- decl %eax
- movd %mm0, (%edx)
- addl $4, %edx
- L(start_src_aligned):
- movq (%ebx), %mm1
- testl %edi, %edx
- psrlq %mm6, %mm5 C retval
- jz L(start_dst_aligned)
- C dst isn't aligned, add 4 to make it so, and pretend the shift is
- C 32 bits extra. Low limb of dst (marked xxx) handled here
- C separately.
- C
- C source ebx
- C --+-------+-------+
- C | mm1 |
- C --+-------+-------+
- C 4mod8 0mod8
- C
- C dest edx
- C --+-------+-------+-------+
- C | xxx |
- C --+-------+-------+-------+
- C 4mod8 0mod8 4mod8
- movq %mm1, %mm0
- addl $32, %ecx C new shift
- psrlq %mm6, %mm0
- movd %ecx, %mm6
- movd %mm0, (%edx)
- addl $4, %edx
- L(start_dst_aligned):
- movq 8(%ebx), %mm3
- negl %ecx
- movq %mm3, %mm2 C mm2 src qword
- addl $64, %ecx
- movd %ecx, %mm7
- psrlq %mm6, %mm1
- leal -12(%ebx,%eax,4), %ebx
- leal -20(%edx,%eax,4), %edx
- psllq %mm7, %mm3
- subl $7, %eax C size-7
- por %mm1, %mm3 C mm3 ready to store
- negl %eax C -(size-7)
- jns L(finish)
- C This loop is the important bit, the rest is just support. Careful
- C instruction scheduling achieves the claimed 1.75 c/l. The
- C relevant parts of the pairing rules are:
- C
- C - mmx loads and stores execute only in the U pipe
- C - only one mmx shift in a pair
- C - wait one cycle before storing an mmx register result
- C - the usual address generation interlock
- C
- C Two qword calculations are slightly interleaved. The instructions
- C marked "C" belong to the second qword, and the "C prev" one is for
- C the second qword from the previous iteration.
- ALIGN(8)
- L(unroll_loop):
- C eax counter, limbs, negative
- C ebx &src[size-12]
- C ecx
- C edx &dst[size-12]
- C esi
- C edi
- C
- C mm0
- C mm1
- C mm2 src qword from -8(%ebx,%eax,4)
- C mm3 dst qword ready to store to -8(%edx,%eax,4)
- C
- C mm5 return value
- C mm6 rshift
- C mm7 lshift
- movq (%ebx,%eax,4), %mm0
- psrlq %mm6, %mm2
- movq %mm0, %mm1
- psllq %mm7, %mm0
- movq %mm3, -8(%edx,%eax,4) C prev
- por %mm2, %mm0
- movq 8(%ebx,%eax,4), %mm3 C
- psrlq %mm6, %mm1 C
- movq %mm0, (%edx,%eax,4)
- movq %mm3, %mm2 C
- psllq %mm7, %mm3 C
- addl $4, %eax
- por %mm1, %mm3 C
- js L(unroll_loop)
- L(finish):
- C eax 0 to 3 representing respectively 3 to 0 limbs remaining
- testb $2, %al
- jnz L(finish_no_two)
- movq (%ebx,%eax,4), %mm0
- psrlq %mm6, %mm2
- movq %mm0, %mm1
- psllq %mm7, %mm0
- movq %mm3, -8(%edx,%eax,4) C prev
- por %mm2, %mm0
- movq %mm1, %mm2
- movq %mm0, %mm3
- addl $2, %eax
- L(finish_no_two):
- C eax 2 or 3 representing respectively 1 or 0 limbs remaining
- C
- C mm2 src prev qword, from -8(%ebx,%eax,4)
- C mm3 dst qword, for -8(%edx,%eax,4)
- testb $1, %al
- popl %edi
- movd %mm5, %eax C retval
- jnz L(finish_zero)
- C One extra limb, destination was aligned.
- C
- C source ebx
- C +-------+---------------+--
- C | | mm2 |
- C +-------+---------------+--
- C
- C dest edx
- C +-------+---------------+---------------+--
- C | | | mm3 |
- C +-------+---------------+---------------+--
- C
- C mm6 = shift
- C mm7 = ecx = 64-shift
- C One extra limb, destination was unaligned.
- C
- C source ebx
- C +-------+---------------+--
- C | | mm2 |
- C +-------+---------------+--
- C
- C dest edx
- C +---------------+---------------+--
- C | | mm3 |
- C +---------------+---------------+--
- C
- C mm6 = shift+32
- C mm7 = ecx = 64-(shift+32)
- C In both cases there's one extra limb of src to fetch and combine
- C with mm2 to make a qword at 8(%edx), and in the aligned case
- C there's a further extra limb of dst to be formed.
- movd 8(%ebx), %mm0
- psrlq %mm6, %mm2
- movq %mm0, %mm1
- psllq %mm7, %mm0
- movq %mm3, (%edx)
- por %mm2, %mm0
- psrlq %mm6, %mm1
- andl $32, %ecx
- popl %ebx
- jz L(finish_one_unaligned)
- C dst was aligned, must store one extra limb
- movd %mm1, 16(%edx)
- L(finish_one_unaligned):
- movq %mm0, 8(%edx)
- emms
- ret
- L(finish_zero):
- C No extra limbs, destination was aligned.
- C
- C source ebx
- C +---------------+--
- C | mm2 |
- C +---------------+--
- C
- C dest edx+4
- C +---------------+---------------+--
- C | | mm3 |
- C +---------------+---------------+--
- C
- C mm6 = shift
- C mm7 = ecx = 64-shift
- C No extra limbs, destination was unaligned.
- C
- C source ebx
- C +---------------+--
- C | mm2 |
- C +---------------+--
- C
- C dest edx+4
- C +-------+---------------+--
- C | | mm3 |
- C +-------+---------------+--
- C
- C mm6 = shift+32
- C mm7 = 64-(shift+32)
- C The movd for the unaligned case is clearly the same data as the
- C movq for the aligned case, it's just a choice between whether one
- C or two limbs should be written.
- movq %mm3, 4(%edx)
- psrlq %mm6, %mm2
- movd %mm2, 12(%edx)
- andl $32, %ecx
- popl %ebx
- jz L(finish_zero_unaligned)
- movq %mm2, 12(%edx)
- L(finish_zero_unaligned):
- emms
- ret
- EPILOGUE()