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

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

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

	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()