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3ba1ef829c
openssl/crypto/bn/asm/x86-mont.pl
Andy Polyakov 3ba1ef829c bn/asm/x86[_64]-mont*.pl: implement slightly alternative page-walking. 
Original strategy for page-walking was adjust stack pointer and then
touch pages in order. This kind of asks for double-fault, because
if touch fails, then signal will be delivered to frame above adjusted
stack pointer. But touching pages prior adjusting stack pointer would
upset valgrind. As compromise let's adjust stack pointer in pages,
touching top of the stack. This still asks for double-fault, but at
least prevents corruption of neighbour stack if allocation is to
overstep the guard page.

Also omit predict-non-taken hints as they reportedly trigger illegal
instructions in some VM setups.

Reviewed-by: Richard Levitte <levitte@openssl.org>
2016-08-22 14:58:32 +02:00

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#! /usr/bin/env perl
# Copyright 2005-2016 The OpenSSL Project Authors. All Rights Reserved.
#
# Licensed under the OpenSSL license (the "License"). You may not use
# this file except in compliance with the License. You can obtain a copy
# in the file LICENSE in the source distribution or at
# https://www.openssl.org/source/license.html
# ====================================================================
# Written by Andy Polyakov <appro@fy.chalmers.se> for the OpenSSL
# project. The module is, however, dual licensed under OpenSSL and
# CRYPTOGAMS licenses depending on where you obtain it. For further
# details see http://www.openssl.org/~appro/cryptogams/.
# ====================================================================
# October 2005
#
# This is a "teaser" code, as it can be improved in several ways...
# First of all non-SSE2 path should be implemented (yes, for now it
# performs Montgomery multiplication/convolution only on SSE2-capable
# CPUs such as P4, others fall down to original code). Then inner loop
# can be unrolled and modulo-scheduled to improve ILP and possibly
# moved to 128-bit XMM register bank (though it would require input
# rearrangement and/or increase bus bandwidth utilization). Dedicated
# squaring procedure should give further performance improvement...
# Yet, for being draft, the code improves rsa512 *sign* benchmark by
# 110%(!), rsa1024 one - by 70% and rsa4096 - by 20%:-)
# December 2006
#
# Modulo-scheduling SSE2 loops results in further 15-20% improvement.
# Integer-only code [being equipped with dedicated squaring procedure]
# gives ~40% on rsa512 sign benchmark...
$0 =~ m/(.*[\/\\])[^\/\\]+$/; $dir=$1;
push(@INC,"${dir}","${dir}../../perlasm");
require "x86asm.pl";
$output = pop;
open STDOUT,">$output";
&asm_init($ARGV[0],$0);
$sse2=0;
for (@ARGV) { $sse2=1 if (/-DOPENSSL_IA32_SSE2/); }
&external_label("OPENSSL_ia32cap_P") if ($sse2);
&function_begin("bn_mul_mont");
$i="edx";
$j="ecx";
$ap="esi"; $tp="esi"; # overlapping variables!!!
$rp="edi"; $bp="edi"; # overlapping variables!!!
$np="ebp";
$num="ebx";
$_num=&DWP(4*0,"esp"); # stack top layout
$_rp=&DWP(4*1,"esp");
$_ap=&DWP(4*2,"esp");
$_bp=&DWP(4*3,"esp");
$_np=&DWP(4*4,"esp");
$_n0=&DWP(4*5,"esp"); $_n0q=&QWP(4*5,"esp");
$_sp=&DWP(4*6,"esp");
$_bpend=&DWP(4*7,"esp");
$frame=32; # size of above frame rounded up to 16n
&xor ("eax","eax");
&mov ("edi",&wparam(5)); # int num
&cmp ("edi",4);
&jl (&label("just_leave"));
&lea ("esi",&wparam(0)); # put aside pointer to argument block
&lea ("edx",&wparam(1)); # load ap
&add ("edi",2); # extra two words on top of tp
&neg ("edi");
&lea ("ebp",&DWP(-$frame,"esp","edi",4)); # future alloca($frame+4*(num+2))
&neg ("edi");
# minimize cache contention by arraning 2K window between stack
# pointer and ap argument [np is also position sensitive vector,
# but it's assumed to be near ap, as it's allocated at ~same
# time].
&mov ("eax","ebp");
&sub ("eax","edx");
&and ("eax",2047);
&sub ("ebp","eax"); # this aligns sp and ap modulo 2048
&xor ("edx","ebp");
&and ("edx",2048);
&xor ("edx",2048);
&sub ("ebp","edx"); # this splits them apart modulo 4096
&and ("ebp",-64); # align to cache line
# An OS-agnostic version of __chkstk.
#
# Some OSes (Windows) insist on stack being "wired" to
# physical memory in strictly sequential manner, i.e. if stack
# allocation spans two pages, then reference to farmost one can
# be punishable by SEGV. But page walking can do good even on
# other OSes, because it guarantees that villain thread hits
# the guard page before it can make damage to innocent one...
&mov ("eax","esp");
&sub ("eax","ebp");
&and ("eax",-4096);
&mov ("edx","esp"); # saved stack pointer!
&lea ("esp",&DWP(0,"ebp","eax"));
&mov ("eax",&DWP(0,"esp"));
&cmp ("esp","ebp");
&ja (&label("page_walk"));
&jmp (&label("page_walk_done"));
&set_label("page_walk",16);
&lea ("esp",&DWP(-4096,"esp"));
&mov ("eax",&DWP(0,"esp"));
&cmp ("esp","ebp");
&ja (&label("page_walk"));
&set_label("page_walk_done");
################################# load argument block...
&mov ("eax",&DWP(0*4,"esi"));# BN_ULONG *rp
&mov ("ebx",&DWP(1*4,"esi"));# const BN_ULONG *ap
&mov ("ecx",&DWP(2*4,"esi"));# const BN_ULONG *bp
&mov ("ebp",&DWP(3*4,"esi"));# const BN_ULONG *np
&mov ("esi",&DWP(4*4,"esi"));# const BN_ULONG *n0
#&mov ("edi",&DWP(5*4,"esi"));# int num
&mov ("esi",&DWP(0,"esi")); # pull n0[0]
&mov ($_rp,"eax"); # ... save a copy of argument block
&mov ($_ap,"ebx");
&mov ($_bp,"ecx");
&mov ($_np,"ebp");
&mov ($_n0,"esi");
&lea ($num,&DWP(-3,"edi")); # num=num-1 to assist modulo-scheduling
#&mov ($_num,$num); # redundant as $num is not reused
&mov ($_sp,"edx"); # saved stack pointer!
if($sse2) {
$acc0="mm0"; # mmx register bank layout
$acc1="mm1";
$car0="mm2";
$car1="mm3";
$mul0="mm4";
$mul1="mm5";
$temp="mm6";
$mask="mm7";
&picmeup("eax","OPENSSL_ia32cap_P");
&bt (&DWP(0,"eax"),26);
&jnc (&label("non_sse2"));
&mov ("eax",-1);
&movd ($mask,"eax"); # mask 32 lower bits
&mov ($ap,$_ap); # load input pointers
&mov ($bp,$_bp);
&mov ($np,$_np);
&xor ($i,$i); # i=0
&xor ($j,$j); # j=0
&movd ($mul0,&DWP(0,$bp)); # bp[0]
&movd ($mul1,&DWP(0,$ap)); # ap[0]
&movd ($car1,&DWP(0,$np)); # np[0]
&pmuludq($mul1,$mul0); # ap[0]*bp[0]
&movq ($car0,$mul1);
&movq ($acc0,$mul1); # I wish movd worked for
&pand ($acc0,$mask); # inter-register transfers
&pmuludq($mul1,$_n0q); # *=n0
&pmuludq($car1,$mul1); # "t[0]"*np[0]*n0
&paddq ($car1,$acc0);
&movd ($acc1,&DWP(4,$np)); # np[1]
&movd ($acc0,&DWP(4,$ap)); # ap[1]
&psrlq ($car0,32);
&psrlq ($car1,32);
&inc ($j); # j++
&set_label("1st",16);
&pmuludq($acc0,$mul0); # ap[j]*bp[0]
&pmuludq($acc1,$mul1); # np[j]*m1
&paddq ($car0,$acc0); # +=c0
&paddq ($car1,$acc1); # +=c1
&movq ($acc0,$car0);
&pand ($acc0,$mask);
&movd ($acc1,&DWP(4,$np,$j,4)); # np[j+1]
&paddq ($car1,$acc0); # +=ap[j]*bp[0];
&movd ($acc0,&DWP(4,$ap,$j,4)); # ap[j+1]
&psrlq ($car0,32);
&movd (&DWP($frame-4,"esp",$j,4),$car1); # tp[j-1]=
&psrlq ($car1,32);
&lea ($j,&DWP(1,$j));
&cmp ($j,$num);
&jl (&label("1st"));
&pmuludq($acc0,$mul0); # ap[num-1]*bp[0]
&pmuludq($acc1,$mul1); # np[num-1]*m1
&paddq ($car0,$acc0); # +=c0
&paddq ($car1,$acc1); # +=c1
&movq ($acc0,$car0);
&pand ($acc0,$mask);
&paddq ($car1,$acc0); # +=ap[num-1]*bp[0];
&movd (&DWP($frame-4,"esp",$j,4),$car1); # tp[num-2]=
&psrlq ($car0,32);
&psrlq ($car1,32);
&paddq ($car1,$car0);
&movq (&QWP($frame,"esp",$num,4),$car1); # tp[num].tp[num-1]
&inc ($i); # i++
&set_label("outer");
&xor ($j,$j); # j=0
&movd ($mul0,&DWP(0,$bp,$i,4)); # bp[i]
&movd ($mul1,&DWP(0,$ap)); # ap[0]
&movd ($temp,&DWP($frame,"esp")); # tp[0]
&movd ($car1,&DWP(0,$np)); # np[0]
&pmuludq($mul1,$mul0); # ap[0]*bp[i]
&paddq ($mul1,$temp); # +=tp[0]
&movq ($acc0,$mul1);
&movq ($car0,$mul1);
&pand ($acc0,$mask);
&pmuludq($mul1,$_n0q); # *=n0
&pmuludq($car1,$mul1);
&paddq ($car1,$acc0);
&movd ($temp,&DWP($frame+4,"esp")); # tp[1]
&movd ($acc1,&DWP(4,$np)); # np[1]
&movd ($acc0,&DWP(4,$ap)); # ap[1]
&psrlq ($car0,32);
&psrlq ($car1,32);
&paddq ($car0,$temp); # +=tp[1]
&inc ($j); # j++
&dec ($num);
&set_label("inner");
&pmuludq($acc0,$mul0); # ap[j]*bp[i]
&pmuludq($acc1,$mul1); # np[j]*m1
&paddq ($car0,$acc0); # +=c0
&paddq ($car1,$acc1); # +=c1
&movq ($acc0,$car0);
&movd ($temp,&DWP($frame+4,"esp",$j,4));# tp[j+1]
&pand ($acc0,$mask);
&movd ($acc1,&DWP(4,$np,$j,4)); # np[j+1]
&paddq ($car1,$acc0); # +=ap[j]*bp[i]+tp[j]
&movd ($acc0,&DWP(4,$ap,$j,4)); # ap[j+1]
&psrlq ($car0,32);
&movd (&DWP($frame-4,"esp",$j,4),$car1);# tp[j-1]=
&psrlq ($car1,32);
&paddq ($car0,$temp); # +=tp[j+1]
&dec ($num);
&lea ($j,&DWP(1,$j)); # j++
&jnz (&label("inner"));
&mov ($num,$j);
&pmuludq($acc0,$mul0); # ap[num-1]*bp[i]
&pmuludq($acc1,$mul1); # np[num-1]*m1
&paddq ($car0,$acc0); # +=c0
&paddq ($car1,$acc1); # +=c1
&movq ($acc0,$car0);
&pand ($acc0,$mask);
&paddq ($car1,$acc0); # +=ap[num-1]*bp[i]+tp[num-1]
&movd (&DWP($frame-4,"esp",$j,4),$car1); # tp[num-2]=
&psrlq ($car0,32);
&psrlq ($car1,32);
&movd ($temp,&DWP($frame+4,"esp",$num,4)); # += tp[num]
&paddq ($car1,$car0);
&paddq ($car1,$temp);
&movq (&QWP($frame,"esp",$num,4),$car1); # tp[num].tp[num-1]
&lea ($i,&DWP(1,$i)); # i++
&cmp ($i,$num);
&jle (&label("outer"));
&emms (); # done with mmx bank
&jmp (&label("common_tail"));
&set_label("non_sse2",16);
}
if (0) {
&mov ("esp",$_sp);
&xor ("eax","eax"); # signal "not fast enough [yet]"
&jmp (&label("just_leave"));
# While the below code provides competitive performance for
# all key lengths on modern Intel cores, it's still more
# than 10% slower for 4096-bit key elsewhere:-( "Competitive"
# means compared to the original integer-only assembler.
# 512-bit RSA sign is better by ~40%, but that's about all
# one can say about all CPUs...
} else {
$inp="esi"; # integer path uses these registers differently
$word="edi";
$carry="ebp";
&mov ($inp,$_ap);
&lea ($carry,&DWP(1,$num));
&mov ($word,$_bp);
&xor ($j,$j); # j=0
&mov ("edx",$inp);
&and ($carry,1); # see if num is even
&sub ("edx",$word); # see if ap==bp
&lea ("eax",&DWP(4,$word,$num,4)); # &bp[num]
&or ($carry,"edx");
&mov ($word,&DWP(0,$word)); # bp[0]
&jz (&label("bn_sqr_mont"));
&mov ($_bpend,"eax");
&mov ("eax",&DWP(0,$inp));
&xor ("edx","edx");
&set_label("mull",16);
&mov ($carry,"edx");
&mul ($word); # ap[j]*bp[0]
&add ($carry,"eax");
&lea ($j,&DWP(1,$j));
&adc ("edx",0);
&mov ("eax",&DWP(0,$inp,$j,4)); # ap[j+1]
&cmp ($j,$num);
&mov (&DWP($frame-4,"esp",$j,4),$carry); # tp[j]=
&jl (&label("mull"));
&mov ($carry,"edx");
&mul ($word); # ap[num-1]*bp[0]
&mov ($word,$_n0);
&add ("eax",$carry);
&mov ($inp,$_np);
&adc ("edx",0);
&imul ($word,&DWP($frame,"esp")); # n0*tp[0]
&mov (&DWP($frame,"esp",$num,4),"eax"); # tp[num-1]=
&xor ($j,$j);
&mov (&DWP($frame+4,"esp",$num,4),"edx"); # tp[num]=
&mov (&DWP($frame+8,"esp",$num,4),$j); # tp[num+1]=
&mov ("eax",&DWP(0,$inp)); # np[0]
&mul ($word); # np[0]*m
&add ("eax",&DWP($frame,"esp")); # +=tp[0]
&mov ("eax",&DWP(4,$inp)); # np[1]
&adc ("edx",0);
&inc ($j);
&jmp (&label("2ndmadd"));
&set_label("1stmadd",16);
&mov ($carry,"edx");
&mul ($word); # ap[j]*bp[i]
&add ($carry,&DWP($frame,"esp",$j,4)); # +=tp[j]
&lea ($j,&DWP(1,$j));
&adc ("edx",0);
&add ($carry,"eax");
&mov ("eax",&DWP(0,$inp,$j,4)); # ap[j+1]
&adc ("edx",0);
&cmp ($j,$num);
&mov (&DWP($frame-4,"esp",$j,4),$carry); # tp[j]=
&jl (&label("1stmadd"));
&mov ($carry,"edx");
&mul ($word); # ap[num-1]*bp[i]
&add ("eax",&DWP($frame,"esp",$num,4)); # +=tp[num-1]
&mov ($word,$_n0);
&adc ("edx",0);
&mov ($inp,$_np);
&add ($carry,"eax");
&adc ("edx",0);
&imul ($word,&DWP($frame,"esp")); # n0*tp[0]
&xor ($j,$j);
&add ("edx",&DWP($frame+4,"esp",$num,4)); # carry+=tp[num]
&mov (&DWP($frame,"esp",$num,4),$carry); # tp[num-1]=
&adc ($j,0);
&mov ("eax",&DWP(0,$inp)); # np[0]
&mov (&DWP($frame+4,"esp",$num,4),"edx"); # tp[num]=
&mov (&DWP($frame+8,"esp",$num,4),$j); # tp[num+1]=
&mul ($word); # np[0]*m
&add ("eax",&DWP($frame,"esp")); # +=tp[0]
&mov ("eax",&DWP(4,$inp)); # np[1]
&adc ("edx",0);
&mov ($j,1);
&set_label("2ndmadd",16);
&mov ($carry,"edx");
&mul ($word); # np[j]*m
&add ($carry,&DWP($frame,"esp",$j,4)); # +=tp[j]
&lea ($j,&DWP(1,$j));
&adc ("edx",0);
&add ($carry,"eax");
&mov ("eax",&DWP(0,$inp,$j,4)); # np[j+1]
&adc ("edx",0);
&cmp ($j,$num);
&mov (&DWP($frame-8,"esp",$j,4),$carry); # tp[j-1]=
&jl (&label("2ndmadd"));
&mov ($carry,"edx");
&mul ($word); # np[j]*m
&add ($carry,&DWP($frame,"esp",$num,4)); # +=tp[num-1]
&adc ("edx",0);
&add ($carry,"eax");
&adc ("edx",0);
&mov (&DWP($frame-4,"esp",$num,4),$carry); # tp[num-2]=
&xor ("eax","eax");
&mov ($j,$_bp); # &bp[i]
&add ("edx",&DWP($frame+4,"esp",$num,4)); # carry+=tp[num]
&adc ("eax",&DWP($frame+8,"esp",$num,4)); # +=tp[num+1]
&lea ($j,&DWP(4,$j));
&mov (&DWP($frame,"esp",$num,4),"edx"); # tp[num-1]=
&cmp ($j,$_bpend);
&mov (&DWP($frame+4,"esp",$num,4),"eax"); # tp[num]=
&je (&label("common_tail"));
&mov ($word,&DWP(0,$j)); # bp[i+1]
&mov ($inp,$_ap);
&mov ($_bp,$j); # &bp[++i]
&xor ($j,$j);
&xor ("edx","edx");
&mov ("eax",&DWP(0,$inp));
&jmp (&label("1stmadd"));
&set_label("bn_sqr_mont",16);
$sbit=$num;
&mov ($_num,$num);
&mov ($_bp,$j); # i=0
&mov ("eax",$word); # ap[0]
&mul ($word); # ap[0]*ap[0]
&mov (&DWP($frame,"esp"),"eax"); # tp[0]=
&mov ($sbit,"edx");
&shr ("edx",1);
&and ($sbit,1);
&inc ($j);
&set_label("sqr",16);
&mov ("eax",&DWP(0,$inp,$j,4)); # ap[j]
&mov ($carry,"edx");
&mul ($word); # ap[j]*ap[0]
&add ("eax",$carry);
&lea ($j,&DWP(1,$j));
&adc ("edx",0);
&lea ($carry,&DWP(0,$sbit,"eax",2));
&shr ("eax",31);
&cmp ($j,$_num);
&mov ($sbit,"eax");
&mov (&DWP($frame-4,"esp",$j,4),$carry); # tp[j]=
&jl (&label("sqr"));
&mov ("eax",&DWP(0,$inp,$j,4)); # ap[num-1]
&mov ($carry,"edx");
&mul ($word); # ap[num-1]*ap[0]
&add ("eax",$carry);
&mov ($word,$_n0);
&adc ("edx",0);
&mov ($inp,$_np);
&lea ($carry,&DWP(0,$sbit,"eax",2));
&imul ($word,&DWP($frame,"esp")); # n0*tp[0]
&shr ("eax",31);
&mov (&DWP($frame,"esp",$j,4),$carry); # tp[num-1]=
&lea ($carry,&DWP(0,"eax","edx",2));
&mov ("eax",&DWP(0,$inp)); # np[0]
&shr ("edx",31);
&mov (&DWP($frame+4,"esp",$j,4),$carry); # tp[num]=
&mov (&DWP($frame+8,"esp",$j,4),"edx"); # tp[num+1]=
&mul ($word); # np[0]*m
&add ("eax",&DWP($frame,"esp")); # +=tp[0]
&mov ($num,$j);
&adc ("edx",0);
&mov ("eax",&DWP(4,$inp)); # np[1]
&mov ($j,1);
&set_label("3rdmadd",16);
&mov ($carry,"edx");
&mul ($word); # np[j]*m
&add ($carry,&DWP($frame,"esp",$j,4)); # +=tp[j]
&adc ("edx",0);
&add ($carry,"eax");
&mov ("eax",&DWP(4,$inp,$j,4)); # np[j+1]
&adc ("edx",0);
&mov (&DWP($frame-4,"esp",$j,4),$carry); # tp[j-1]=
&mov ($carry,"edx");
&mul ($word); # np[j+1]*m
&add ($carry,&DWP($frame+4,"esp",$j,4)); # +=tp[j+1]
&lea ($j,&DWP(2,$j));
&adc ("edx",0);
&add ($carry,"eax");
&mov ("eax",&DWP(0,$inp,$j,4)); # np[j+2]
&adc ("edx",0);
&cmp ($j,$num);
&mov (&DWP($frame-8,"esp",$j,4),$carry); # tp[j]=
&jl (&label("3rdmadd"));
&mov ($carry,"edx");
&mul ($word); # np[j]*m
&add ($carry,&DWP($frame,"esp",$num,4)); # +=tp[num-1]
&adc ("edx",0);
&add ($carry,"eax");
&adc ("edx",0);
&mov (&DWP($frame-4,"esp",$num,4),$carry); # tp[num-2]=
&mov ($j,$_bp); # i
&xor ("eax","eax");
&mov ($inp,$_ap);
&add ("edx",&DWP($frame+4,"esp",$num,4)); # carry+=tp[num]
&adc ("eax",&DWP($frame+8,"esp",$num,4)); # +=tp[num+1]
&mov (&DWP($frame,"esp",$num,4),"edx"); # tp[num-1]=
&cmp ($j,$num);
&mov (&DWP($frame+4,"esp",$num,4),"eax"); # tp[num]=
&je (&label("common_tail"));
&mov ($word,&DWP(4,$inp,$j,4)); # ap[i]
&lea ($j,&DWP(1,$j));
&mov ("eax",$word);
&mov ($_bp,$j); # ++i
&mul ($word); # ap[i]*ap[i]
&add ("eax",&DWP($frame,"esp",$j,4)); # +=tp[i]
&adc ("edx",0);
&mov (&DWP($frame,"esp",$j,4),"eax"); # tp[i]=
&xor ($carry,$carry);
&cmp ($j,$num);
&lea ($j,&DWP(1,$j));
&je (&label("sqrlast"));
&mov ($sbit,"edx"); # zaps $num
&shr ("edx",1);
&and ($sbit,1);
&set_label("sqradd",16);
&mov ("eax",&DWP(0,$inp,$j,4)); # ap[j]
&mov ($carry,"edx");
&mul ($word); # ap[j]*ap[i]
&add ("eax",$carry);
&lea ($carry,&DWP(0,"eax","eax"));
&adc ("edx",0);
&shr ("eax",31);
&add ($carry,&DWP($frame,"esp",$j,4)); # +=tp[j]
&lea ($j,&DWP(1,$j));
&adc ("eax",0);
&add ($carry,$sbit);
&adc ("eax",0);
&cmp ($j,$_num);
&mov (&DWP($frame-4,"esp",$j,4),$carry); # tp[j]=
&mov ($sbit,"eax");
&jle (&label("sqradd"));
&mov ($carry,"edx");
&add ("edx","edx");
&shr ($carry,31);
&add ("edx",$sbit);
&adc ($carry,0);
&set_label("sqrlast");
&mov ($word,$_n0);
&mov ($inp,$_np);
&imul ($word,&DWP($frame,"esp")); # n0*tp[0]
&add ("edx",&DWP($frame,"esp",$j,4)); # +=tp[num]
&mov ("eax",&DWP(0,$inp)); # np[0]
&adc ($carry,0);
&mov (&DWP($frame,"esp",$j,4),"edx"); # tp[num]=
&mov (&DWP($frame+4,"esp",$j,4),$carry); # tp[num+1]=
&mul ($word); # np[0]*m
&add ("eax",&DWP($frame,"esp")); # +=tp[0]
&lea ($num,&DWP(-1,$j));
&adc ("edx",0);
&mov ($j,1);
&mov ("eax",&DWP(4,$inp)); # np[1]
&jmp (&label("3rdmadd"));
}
&set_label("common_tail",16);
&mov ($np,$_np); # load modulus pointer
&mov ($rp,$_rp); # load result pointer
&lea ($tp,&DWP($frame,"esp")); # [$ap and $bp are zapped]
&mov ("eax",&DWP(0,$tp)); # tp[0]
&mov ($j,$num); # j=num-1
&xor ($i,$i); # i=0 and clear CF!
&set_label("sub",16);
&sbb ("eax",&DWP(0,$np,$i,4));
&mov (&DWP(0,$rp,$i,4),"eax"); # rp[i]=tp[i]-np[i]
&dec ($j); # doesn't affect CF!
&mov ("eax",&DWP(4,$tp,$i,4)); # tp[i+1]
&lea ($i,&DWP(1,$i)); # i++
&jge (&label("sub"));
&sbb ("eax",0); # handle upmost overflow bit
&and ($tp,"eax");
&not ("eax");
&mov ($np,$rp);
&and ($np,"eax");
&or ($tp,$np); # tp=carry?tp:rp
&set_label("copy",16); # copy or in-place refresh
&mov ("eax",&DWP(0,$tp,$num,4));
&mov (&DWP(0,$rp,$num,4),"eax"); # rp[i]=tp[i]
&mov (&DWP($frame,"esp",$num,4),$j); # zap temporary vector
&dec ($num);
&jge (&label("copy"));
&mov ("esp",$_sp); # pull saved stack pointer
&mov ("eax",1);
&set_label("just_leave");
&function_end("bn_mul_mont");
&asciz("Montgomery Multiplication for x86, CRYPTOGAMS by <appro\@openssl.org>");
&asm_finish();
close STDOUT;
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