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/* 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 2 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, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*
* 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
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