--- /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