--- /dev/null
+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()
projects / msp430-gcc.git / blobdiff