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+dnl x86 mpn_divrem_1 -- mpn by limb division extending to fractional quotient.
+
+dnl Copyright 1999-2003, 2007 Free Software Foundation, Inc.
+
+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 modify
+dnl it under the terms of either:
+dnl
+dnl * the GNU Lesser General Public License as published by the Free
+dnl Software Foundation; either version 3 of the License, or (at your
+dnl option) any later version.
+dnl
+dnl or
+dnl
+dnl * the GNU General Public License as published by the Free Software
+dnl Foundation; either version 2 of the License, or (at your option) any
+dnl later version.
+dnl
+dnl or both in parallel, as here.
+dnl
+dnl The GNU MP Library is distributed in the hope that it will be useful, but
+dnl WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+dnl or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+dnl for more details.
+dnl
+dnl You should have received copies of the GNU General Public License and the
+dnl GNU Lesser General Public License along with the GNU MP Library. If not,
+dnl see https://www.gnu.org/licenses/.
+
+include(`../config.m4')
+
+
+C cycles/limb
+C 486 approx 43 maybe
+C P5 44
+C P6 39
+C P6MMX 39
+C K6 22
+C K7 42
+C P4 58
+
+
+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 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 advantage that we get the desired divl
+C instruction even when gcc is not being used (when longlong.h only has the
+C rather slow generic C udiv_qrnnd().
+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 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 Notes for P5:
+C
+C It might be thought that moving the load down to pair with the store would
+C save 1 cycle, but that doesn't seem to happen in practice, and in any case
+C would be a mere 2.2% saving, so it's hardly worth bothering about.
+C
+C A mul-by-inverse might be a possibility for P5, as done in
+C mpn/x86/pentium/mod_1.asm. The number of auxiliary instructions required
+C is a hinderance, but there could be a 10-15% speedup available.
+C
+C
+C Notes for K6:
+C
+C K6 has its own version of this code, using loop and paying attention to
+C cache line boundary crossings. The target 20 c/l can be had with the
+C decl+jnz of the present code by pairing up the load and store in the
+C loops. But it's considered easier not to introduce complexity just for
+C that, but instead let k6 have its own code.
+C
+
+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 L(fraction)
+
+ leal -4(%ebx,%ebp,4), %ebx C dst one limb below integer part
+ jmp L(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)
+ decl %ecx
+ jnz 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)
+ decl %ecx
+ jnz 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()