+++ /dev/null
-dnl x86 mpn_divrem_1 -- mpn by limb division extending to fractional quotient.
-
-dnl Copyright (C) 1999, 2000 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 2.1 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
-dnl License along with the GNU MP Library; see the file COPYING.LIB. If
-dnl not, write to the Free Software Foundation, Inc., 59 Temple Place -
-dnl Suite 330, Boston, MA 02111-1307, USA.
-
-
-dnl cycles/limb
-dnl K6 20
-dnl P5 44
-dnl P6 39
-dnl 486 approx 43 maybe
-dnl
-dnl
-dnl The following have their own optimized divrem_1 implementations, but
-dnl for reference the code here runs as follows.
-dnl
-dnl cycles/limb
-dnl P6MMX 39
-dnl K7 42
-
-
-include(`../config.m4')
-
-
-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
-C Divide src,size by divisor and store the quotient in dst+xsize,size.
-C Extend the division to fractional quotient limbs in dst,xsize. Return the
-C remainder. Either or both xsize and size can be 0.
-C
-C mpn_divrem_1c takes a carry parameter which is an initial high limb,
-C effectively one extra limb at the top of src,size. Must have
-C carry<divisor.
-C
-C
-C Essentially the code is the same as the division based part of
-C mpn/generic/divrem_1.c, but has the following advantages.
-C
-C - If gcc isn't being used then divrem_1.c will get the generic C
-C udiv_qrnnd() and be rather slow.
-C
-C - On K6, using the loop instruction is a 10% speedup, but gcc doesn't
-C generate that instruction (as of gcc 2.95.2 at least).
-C
-C A test is done to see if the high limb is less the the divisor, and if so
-C one less div is done. A div is between 20 and 40 cycles on the various
-C x86s, so assuming high<divisor about half the time, then this test saves
-C half that amount. The branch misprediction penalty on each chip is less
-C than half a div.
-C
-C
-C K6: Back-to-back div instructions run at 20 cycles, the same as the loop
-C here, so it seems there's nothing to gain by rearranging the loop.
-C Pairing the mov and loop instructions was found to gain nothing. (The
-C same is true of the mpn/x86/mod_1.asm loop.)
-C
-C With a "decl/jnz" rather than a "loop" this code runs at 22 cycles.
-C The loop_or_decljnz macro is an easy way to get a 10% speedup.
-C
-C The fast K6 multiply might be thought to suit a multiply-by-inverse,
-C but that algorithm has been found to suffer from the releatively poor
-C carry handling on K6 and too many auxiliary instructions. The
-C fractional part however could be done at about 13 c/l.
-C
-C P5: Moving the load down to pair with the store might save 1 cycle, but
-C that doesn't seem worth bothering with, since it'd be only a 2.2%
-C saving.
-C
-C Again here the auxiliary instructions hinder a multiply-by-inverse,
-C though there might be a 10-15% speedup available
-
-
-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(16)
-
-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
-
- movl PARAM_CARRY, %edx
- jz LF(mpn_divrem_1,fraction)
-
- leal -4(%ebx,%ebp,4), %ebx C dst one limb below integer part
- jmp LF(mpn_divrem_1,integer_top)
-
-EPILOGUE()
-
-
-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
-
- 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_or_decljnz 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_or_decljnz 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.family
-
- rep
- stosl
-
- popl %esi
- popl %edi
- ret
-EPILOGUE()
projects / ghc-hetmet.git / blobdiff