/* Intel Pentium-4 mpn_sub_n -- mpn subtraction.
*
* Copyright 2001, 2002 Free Software Foundation, Inc.
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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.
*/
#include "sysdep.h"
#include "asm-syntax.h"
/*******************
* mpi_limb_t
* _gcry_mpih_sub_n( mpi_ptr_t res_ptr, (sp + 4)
* mpi_ptr_t s1_ptr, (sp + 8)
* mpi_ptr_t s2_ptr, (sp + 12)
* mpi_size_t size) (sp + 16)
*
* P4 Willamette, Northwood: 4.0 cycles/limb if dst!=src1 and dst!=src2
* 6.0 cycles/limb if dst==src1 or dst==src2
* P4 Prescott: >= 5 cycles/limb
*
* The main loop code is 2x unrolled so that the carry bit can alternate
* between mm0 and mm1.
*/
.text
ALIGN (3)
.globl C_SYMBOL_NAME(_gcry_mpih_sub_n)
C_SYMBOL_NAME(_gcry_mpih_sub_n:)
pxor %mm0, %mm0
.Lstart_nc:
movl 8(%esp), %eax
movl %ebx, 8(%esp)
movl 12(%esp), %ebx
movl 4(%esp), %edx
movl 16(%esp), %ecx
leal (%eax,%ecx,4), %eax
leal (%ebx,%ecx,4), %ebx
leal (%edx,%ecx,4), %edx
negl %ecx
.Ltop:
/*
C eax src1 end
C ebx src2 end
C ecx counter, limbs, negative
C edx dst end
C mm0 carry bit
*/
movd (%eax,%ecx,4), %mm1
movd (%ebx,%ecx,4), %mm2
psubq %mm2, %mm1
psubq %mm0, %mm1
movd %mm1, (%edx,%ecx,4)
psrlq $63, %mm1
addl $1, %ecx
jz .Ldone_mm1
movd (%eax,%ecx,4), %mm0
movd (%ebx,%ecx,4), %mm2
psubq %mm2, %mm0
psubq %mm1, %mm0
movd %mm0, (%edx,%ecx,4)
psrlq $63, %mm0
addl $1, %ecx
jnz .Ltop
movd %mm0, %eax
movl 8(%esp), %ebx
emms
ret
.Ldone_mm1:
movd %mm1, %eax
movl 8(%esp), %ebx
emms
ret
