divrem_1.asm
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上传日期:2022-08-06
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- dnl AMD K6 mpn_divrem_1 -- mpn by limb division.
- dnl Copyright 1999, 2000, 2001, 2002, 2003, 2007 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 K6: 20 cycles/limb
- C mp_limb_t mpn_divrem_1 (mp_ptr dst, mp_size_t xsize,
- C mp_srcptr src, mp_size_t size, 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, mp_limb_t divisor,
- C mp_limb_t carry);
- C
- C The code here is basically the same as mpn/x86/divrem_1.asm, but uses loop
- C instead of decl+jnz, since it comes out 2 cycles/limb faster.
- C
- C A test is done to see if the high limb is less than the divisor, and if so
- C one less div is done. A div is 20 cycles, so assuming high<divisor about
- C half the time, then this test saves half that amount. The branch
- C misprediction penalty is less than that.
- C
- C Back-to-back div instructions run at 20 cycles, the same as the loop here,
- C so it seems there's nothing to gain by rearranging the loop. Pairing the
- C mov and loop instructions was found to gain nothing.
- C
- C Enhancements:
- C
- C The low-latency K6 multiply might be thought to suit a mul-by-inverse, but
- C that algorithm has been found to suffer from the relatively poor carry
- C handling on K6 and too many auxiliary instructions. The fractional part
- C however could be done at about 13 c/l, if it mattered enough.
- defframe(PARAM_CARRY, 24)
- defframe(PARAM_DIVISOR,20)
- defframe(PARAM_SIZE, 16)
- defframe(PARAM_SRC, 12)
- defframe(PARAM_XSIZE, 8)
- defframe(PARAM_DST, 4)
- TEXT
- ALIGN(32)
- PROLOGUE(mpn_divrem_1c)
- deflit(`FRAME',0)
- movl PARAM_SIZE, %ecx
- pushl %edi FRAME_pushl()
- movl PARAM_SRC, %edi
- pushl %esi FRAME_pushl()
- movl PARAM_DIVISOR, %esi
- pushl %ebx FRAME_pushl()
- movl PARAM_DST, %ebx
- pushl %ebp FRAME_pushl()
- movl PARAM_XSIZE, %ebp
- orl %ecx, %ecx C size
- movl PARAM_CARRY, %edx
- jz L(fraction) C if size==0
- leal -4(%ebx,%ebp,4), %ebx C dst one limb below integer part
- jmp L(integer_top)
- EPILOGUE()
- ALIGN(16)
- PROLOGUE(mpn_divrem_1)
- deflit(`FRAME',0)
- movl PARAM_SIZE, %ecx
- pushl %edi FRAME_pushl()
- movl PARAM_SRC, %edi
- pushl %esi FRAME_pushl()
- movl PARAM_DIVISOR, %esi
- orl %ecx,%ecx C size
- jz L(size_zero)
- pushl %ebx FRAME_pushl()
- movl -4(%edi,%ecx,4), %eax C src high limb
- xorl %edx, %edx
- movl PARAM_DST, %ebx
- pushl %ebp FRAME_pushl()
- movl PARAM_XSIZE, %ebp
- cmpl %esi, %eax
- leal -4(%ebx,%ebp,4), %ebx C dst one limb below integer part
- jae L(integer_entry)
- C high<divisor, so high of dst is zero, and avoid one div
- movl %edx, (%ebx,%ecx,4)
- decl %ecx
- movl %eax, %edx
- jz L(fraction)
- L(integer_top):
- C eax scratch (quotient)
- C ebx dst+4*xsize-4
- C ecx counter
- C edx scratch (remainder)
- C esi divisor
- C edi src
- C ebp xsize
- movl -4(%edi,%ecx,4), %eax
- L(integer_entry):
- divl %esi
- movl %eax, (%ebx,%ecx,4)
- loop L(integer_top)
- L(fraction):
- orl %ebp, %ecx
- jz L(done)
- movl PARAM_DST, %ebx
- L(fraction_top):
- C eax scratch (quotient)
- C ebx dst
- C ecx counter
- C edx scratch (remainder)
- C esi divisor
- C edi
- C ebp
- xorl %eax, %eax
- divl %esi
- movl %eax, -4(%ebx,%ecx,4)
- loop L(fraction_top)
- L(done):
- popl %ebp
- movl %edx, %eax
- popl %ebx
- popl %esi
- popl %edi
- ret
- L(size_zero):
- deflit(`FRAME',8)
- movl PARAM_XSIZE, %ecx
- xorl %eax, %eax
- movl PARAM_DST, %edi
- cld C better safe than sorry, see mpn/x86/README
- rep
- stosl
- popl %esi
- popl %edi
- ret
- EPILOGUE()