gnupg/mpi/i586/mpih-rshift.S

/* i80586   rshift
 *
 *      Copyright (C) 1992, 1994, 1998,
 *                    2001 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 *
 * Note: This code is heavily based on the GNU MP Library.
 *	 Actually it's the same code with only minor changes in the
 *	 way the data is stored; this is to support the abstraction
 *	 of an optional secure memory allocation which may be used
 *	 to avoid revealing of sensitive data due to paging etc.
 *	 The GNU MP Library itself is published under the LGPL;
 *	 however I decided to publish this code under the plain GPL.
 */


#include "sysdep.h"
#include "asm-syntax.h"



/*******************
 * mpi_limb_t
 * mpihelp_rshift( mpi_ptr_t wp,	(sp + 4)
 *		   mpi_ptr_t up,	(sp + 8)
 *		   mpi_size_t usize,	(sp + 12)
 *		   unsigned cnt)	(sp + 16)
 */

.text
	ALIGN (3)
	.globl C_SYMBOL_NAME(mpihelp_rshift)
C_SYMBOL_NAME(mpihelp_rshift:)
	pushl	%edi
	pushl	%esi
	pushl	%ebx
	pushl	%ebp

	movl	20(%esp),%edi		/* res_ptr */
	movl	24(%esp),%esi		/* s_ptr */
	movl	28(%esp),%ebp		/* size */
	movl	32(%esp),%ecx		/* cnt */

/* We can use faster code for shift-by-1 under certain conditions.  */
	cmp	$1,%ecx
	jne	Rnormal
	leal	4(%edi),%eax
	cmpl	%esi,%eax
	jnc	Rspecial		/* jump if res_ptr + 1 >= s_ptr */
	leal	(%edi,%ebp,4),%eax
	cmpl	%eax,%esi
	jnc	Rspecial		/* jump if s_ptr >= res_ptr + size */

Rnormal:
	movl	(%esi),%edx
	addl	$4,%esi
	xorl	%eax,%eax
	shrdl	%cl,%edx,%eax		/* compute carry limb */
	pushl	%eax			/* push carry limb onto stack */

	decl	%ebp
	pushl	%ebp
	shrl	$3,%ebp
	jz	Rend

	movl	(%edi),%eax		/* fetch destination cache line */

	ALIGN	(2)
Roop:	movl	28(%edi),%eax		/* fetch destination cache line */
	movl	%edx,%ebx

	movl	(%esi),%eax
	movl	4(%esi),%edx
	shrdl	%cl,%eax,%ebx
	shrdl	%cl,%edx,%eax
	movl	%ebx,(%edi)
	movl	%eax,4(%edi)

	movl	8(%esi),%ebx
	movl	12(%esi),%eax
	shrdl	%cl,%ebx,%edx
	shrdl	%cl,%eax,%ebx
	movl	%edx,8(%edi)
	movl	%ebx,12(%edi)

	movl	16(%esi),%edx
	movl	20(%esi),%ebx
	shrdl	%cl,%edx,%eax
	shrdl	%cl,%ebx,%edx
	movl	%eax,16(%edi)
	movl	%edx,20(%edi)

	movl	24(%esi),%eax
	movl	28(%esi),%edx
	shrdl	%cl,%eax,%ebx
	shrdl	%cl,%edx,%eax
	movl	%ebx,24(%edi)
	movl	%eax,28(%edi)

	addl	$32,%esi
	addl	$32,%edi
	decl	%ebp
	jnz	Roop

Rend:	popl	%ebp
	andl	$7,%ebp
	jz	Rend2
Roop2:	movl	(%esi),%eax
	shrdl	%cl,%eax,%edx		/* compute result limb */
	movl	%edx,(%edi)
	movl	%eax,%edx
	addl	$4,%esi
	addl	$4,%edi
	decl	%ebp
	jnz	Roop2

Rend2:	shrl	%cl,%edx		/* compute most significant limb */
	movl	%edx,(%edi)		/* store it */

	popl	%eax			/* pop carry limb */

	popl	%ebp
	popl	%ebx
	popl	%esi
	popl	%edi
	ret

/* We loop from least significant end of the arrays, which is only
   permissable if the source and destination don't overlap, since the
   function is documented to work for overlapping source and destination.
*/

Rspecial:
	leal	-4(%edi,%ebp,4),%edi
	leal	-4(%esi,%ebp,4),%esi

	movl	(%esi),%edx
	subl	$4,%esi

	decl	%ebp
	pushl	%ebp
	shrl	$3,%ebp

	shrl	$1,%edx
	incl	%ebp
	decl	%ebp
	jz	RLend

	movl	(%edi),%eax		/* fetch destination cache line */

	ALIGN	(2)
RLoop:	movl	-28(%edi),%eax		/* fetch destination cache line */
	movl	%edx,%ebx

	movl	(%esi),%eax
	movl	-4(%esi),%edx
	rcrl	$1,%eax
	movl	%ebx,(%edi)
	rcrl	$1,%edx
	movl	%eax,-4(%edi)

	movl	-8(%esi),%ebx
	movl	-12(%esi),%eax
	rcrl	$1,%ebx
	movl	%edx,-8(%edi)
	rcrl	$1,%eax
	movl	%ebx,-12(%edi)

	movl	-16(%esi),%edx
	movl	-20(%esi),%ebx
	rcrl	$1,%edx
	movl	%eax,-16(%edi)
	rcrl	$1,%ebx
	movl	%edx,-20(%edi)

	movl	-24(%esi),%eax
	movl	-28(%esi),%edx
	rcrl	$1,%eax
	movl	%ebx,-24(%edi)
	rcrl	$1,%edx
	movl	%eax,-28(%edi)

	leal	-32(%esi),%esi		/* use leal not to clobber carry */
	leal	-32(%edi),%edi
	decl	%ebp
	jnz	RLoop

RLend:	popl	%ebp
	sbbl	%eax,%eax		/* save carry in %eax */
	andl	$7,%ebp
	jz	RLend2
	addl	%eax,%eax		/* restore carry from eax */
RLoop2: movl	%edx,%ebx
	movl	(%esi),%edx
	rcrl	$1,%edx
	movl	%ebx,(%edi)

	leal	-4(%esi),%esi		/* use leal not to clobber carry */
	leal	-4(%edi),%edi
	decl	%ebp
	jnz	RLoop2

	jmp	RL1
RLend2: addl	%eax,%eax		/* restore carry from eax */
RL1:	movl	%edx,(%edi)		/* store last limb */

	movl	$0,%eax
	rcrl	$1,%eax

	popl	%ebp
	popl	%ebx
	popl	%esi
	popl	%edi
	ret