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boringssl/crypto/modes/asm/ghash-x86.pl
Brian Smith 18a37a4211 Remove unused "pure" MMX x86 GCM implementation. 
BoringSSL will always use the SSE version so this is all dead code.

Change-Id: I0f3b51ee29144b5c83d2553c92bebae901b6366f
Reviewed-on: https://boringssl-review.googlesource.com/13023
Reviewed-by: Adam Langley <alangley@gmail.com>
2017-01-13 01:19:01 +00:00

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#!/usr/bin/env perl
#
# ====================================================================
# Written by Andy Polyakov <appro@openssl.org> 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/.
# ====================================================================
#
# March, May, June 2010
#
# The module implements "4-bit" GCM GHASH function and underlying
# single multiplication operation in GF(2^128). "4-bit" means that it
# uses 256 bytes per-key table [+64/128 bytes fixed table]. It has two
# code paths: vanilla x86 and vanilla SSE. Former will be executed on
# 486 and Pentium, latter on all others. SSE GHASH features so called
# "528B" variant of "4-bit" method utilizing additional 256+16 bytes
# of per-key storage [+512 bytes shared table]. Performance results
# are for streamed GHASH subroutine and are expressed in cycles per
# processed byte, less is better:
#
# gcc 2.95.3(*) SSE assembler x86 assembler
#
# Pentium 105/111(**) - 50
# PIII 68 /75 12.2 24
# P4 125/125 17.8 84(***)
# Opteron 66 /70 10.1 30
# Core2 54 /67 8.4 18
# Atom 105/105 16.8 53
# VIA Nano 69 /71 13.0 27
#
# (*) gcc 3.4.x was observed to generate few percent slower code,
# which is one of reasons why 2.95.3 results were chosen,
# another reason is lack of 3.4.x results for older CPUs;
# comparison with SSE results is not completely fair, because C
# results are for vanilla "256B" implementation, while
# assembler results are for "528B";-)
# (**) second number is result for code compiled with -fPIC flag,
# which is actually more relevant, because assembler code is
# position-independent;
# (***) see comment in non-MMX routine for further details;
#
# To summarize, it's >2-5 times faster than gcc-generated code. To
# anchor it to something else SHA1 assembler processes one byte in
# ~7 cycles on contemporary x86 cores. As for choice of MMX/SSE
# in particular, see comment at the end of the file...
# May 2010
#
# Add PCLMULQDQ version performing at 2.10 cycles per processed byte.
# The question is how close is it to theoretical limit? The pclmulqdq
# instruction latency appears to be 14 cycles and there can't be more
# than 2 of them executing at any given time. This means that single
# Karatsuba multiplication would take 28 cycles *plus* few cycles for
# pre- and post-processing. Then multiplication has to be followed by
# modulo-reduction. Given that aggregated reduction method [see
# "Carry-less Multiplication and Its Usage for Computing the GCM Mode"
# white paper by Intel] allows you to perform reduction only once in
# a while we can assume that asymptotic performance can be estimated
# as (28+Tmod/Naggr)/16, where Tmod is time to perform reduction
# and Naggr is the aggregation factor.
#
# Before we proceed to this implementation let's have closer look at
# the best-performing code suggested by Intel in their white paper.
# By tracing inter-register dependencies Tmod is estimated as ~19
# cycles and Naggr chosen by Intel is 4, resulting in 2.05 cycles per
# processed byte. As implied, this is quite optimistic estimate,
# because it does not account for Karatsuba pre- and post-processing,
# which for a single multiplication is ~5 cycles. Unfortunately Intel
# does not provide performance data for GHASH alone. But benchmarking
# AES_GCM_encrypt ripped out of Fig. 15 of the white paper with aadt
# alone resulted in 2.46 cycles per byte of out 16KB buffer. Note that
# the result accounts even for pre-computing of degrees of the hash
# key H, but its portion is negligible at 16KB buffer size.
#
# Moving on to the implementation in question. Tmod is estimated as
# ~13 cycles and Naggr is 2, giving asymptotic performance of ...
# 2.16. How is it possible that measured performance is better than
# optimistic theoretical estimate? There is one thing Intel failed
# to recognize. By serializing GHASH with CTR in same subroutine
# former's performance is really limited to above (Tmul + Tmod/Naggr)
# equation. But if GHASH procedure is detached, the modulo-reduction
# can be interleaved with Naggr-1 multiplications at instruction level
# and under ideal conditions even disappear from the equation. So that
# optimistic theoretical estimate for this implementation is ...
# 28/16=1.75, and not 2.16. Well, it's probably way too optimistic,
# at least for such small Naggr. I'd argue that (28+Tproc/Naggr),
# where Tproc is time required for Karatsuba pre- and post-processing,
# is more realistic estimate. In this case it gives ... 1.91 cycles.
# Or in other words, depending on how well we can interleave reduction
# and one of the two multiplications the performance should be betwen
# 1.91 and 2.16. As already mentioned, this implementation processes
# one byte out of 8KB buffer in 2.10 cycles, while x86_64 counterpart
# - in 2.02. x86_64 performance is better, because larger register
# bank allows to interleave reduction and multiplication better.
#
# Does it make sense to increase Naggr? To start with it's virtually
# impossible in 32-bit mode, because of limited register bank
# capacity. Otherwise improvement has to be weighed agiainst slower
# setup, as well as code size and complexity increase. As even
# optimistic estimate doesn't promise 30% performance improvement,
# there are currently no plans to increase Naggr.
#
# Special thanks to David Woodhouse <dwmw2@infradead.org> for
# providing access to a Westmere-based system on behalf of Intel
# Open Source Technology Centre.
# January 2010
#
# Tweaked to optimize transitions between integer and FP operations
# on same XMM register, PCLMULQDQ subroutine was measured to process
# one byte in 2.07 cycles on Sandy Bridge, and in 2.12 - on Westmere.
# The minor regression on Westmere is outweighed by ~15% improvement
# on Sandy Bridge. Strangely enough attempt to modify 64-bit code in
# similar manner resulted in almost 20% degradation on Sandy Bridge,
# where original 64-bit code processes one byte in 1.95 cycles.
#####################################################################
# For reference, AMD Bulldozer processes one byte in 1.98 cycles in
# 32-bit mode and 1.89 in 64-bit.
# February 2013
#
# Overhaul: aggregate Karatsuba post-processing, improve ILP in
# reduction_alg9. Resulting performance is 1.96 cycles per byte on
# Westmere, 1.95 - on Sandy/Ivy Bridge, 1.76 - on Bulldozer.
$0 =~ m/(.*[\/\\])[^\/\\]+$/; $dir=$1;
push(@INC,"${dir}","${dir}../../perlasm");
require "x86asm.pl";
$output=pop;
open STDOUT,">$output";
&asm_init($ARGV[0],"ghash-x86.pl",$x86only = $ARGV[$#ARGV] eq "386");
$sse2=0;
for (@ARGV) { $sse2=1 if (/-DOPENSSL_IA32_SSE2/); }
($Zhh,$Zhl,$Zlh,$Zll) = ("ebp","edx","ecx","ebx");
$inp = "edi";
$Htbl = "esi";
$unroll = 0; # Affects x86 loop. Folded loop performs ~7% worse
# than unrolled, which has to be weighted against
# 2.5x x86-specific code size reduction.
sub x86_loop {
my $off = shift;
my $rem = "eax";
&mov ($Zhh,&DWP(4,$Htbl,$Zll));
&mov ($Zhl,&DWP(0,$Htbl,$Zll));
&mov ($Zlh,&DWP(12,$Htbl,$Zll));
&mov ($Zll,&DWP(8,$Htbl,$Zll));
&xor ($rem,$rem); # avoid partial register stalls on PIII
# shrd practically kills P4, 2.5x deterioration, but P4 has
# MMX code-path to execute. shrd runs tad faster [than twice
# the shifts, move's and or's] on pre-MMX Pentium (as well as
# PIII and Core2), *but* minimizes code size, spares register
# and thus allows to fold the loop...
if (!$unroll) {
my $cnt = $inp;
&mov ($cnt,15);
&jmp (&label("x86_loop"));
&set_label("x86_loop",16);
for($i=1;$i<=2;$i++) {
&mov (&LB($rem),&LB($Zll));
&shrd ($Zll,$Zlh,4);
&and (&LB($rem),0xf);
&shrd ($Zlh,$Zhl,4);
&shrd ($Zhl,$Zhh,4);
&shr ($Zhh,4);
&xor ($Zhh,&DWP($off+16,"esp",$rem,4));
&mov (&LB($rem),&BP($off,"esp",$cnt));
if ($i&1) {
&and (&LB($rem),0xf0);
} else {
&shl (&LB($rem),4);
}
&xor ($Zll,&DWP(8,$Htbl,$rem));
&xor ($Zlh,&DWP(12,$Htbl,$rem));
&xor ($Zhl,&DWP(0,$Htbl,$rem));
&xor ($Zhh,&DWP(4,$Htbl,$rem));
if ($i&1) {
&dec ($cnt);
&js (&label("x86_break"));
} else {
&jmp (&label("x86_loop"));
}
}
&set_label("x86_break",16);
} else {
for($i=1;$i<32;$i++) {
&comment($i);
&mov (&LB($rem),&LB($Zll));
&shrd ($Zll,$Zlh,4);
&and (&LB($rem),0xf);
&shrd ($Zlh,$Zhl,4);
&shrd ($Zhl,$Zhh,4);
&shr ($Zhh,4);
&xor ($Zhh,&DWP($off+16,"esp",$rem,4));
if ($i&1) {
&mov (&LB($rem),&BP($off+15-($i>>1),"esp"));
&and (&LB($rem),0xf0);
} else {
&mov (&LB($rem),&BP($off+15-($i>>1),"esp"));
&shl (&LB($rem),4);
}
&xor ($Zll,&DWP(8,$Htbl,$rem));
&xor ($Zlh,&DWP(12,$Htbl,$rem));
&xor ($Zhl,&DWP(0,$Htbl,$rem));
&xor ($Zhh,&DWP(4,$Htbl,$rem));
}
}
&bswap ($Zll);
&bswap ($Zlh);
&bswap ($Zhl);
if (!$x86only) {
&bswap ($Zhh);
} else {
&mov ("eax",$Zhh);
&bswap ("eax");
&mov ($Zhh,"eax");
}
}
if ($unroll) {
&function_begin_B("_x86_gmult_4bit_inner");
&x86_loop(4);
&ret ();
&function_end_B("_x86_gmult_4bit_inner");
}
sub deposit_rem_4bit {
my $bias = shift;
&mov (&DWP($bias+0, "esp"),0x0000<<16);
&mov (&DWP($bias+4, "esp"),0x1C20<<16);
&mov (&DWP($bias+8, "esp"),0x3840<<16);
&mov (&DWP($bias+12,"esp"),0x2460<<16);
&mov (&DWP($bias+16,"esp"),0x7080<<16);
&mov (&DWP($bias+20,"esp"),0x6CA0<<16);
&mov (&DWP($bias+24,"esp"),0x48C0<<16);
&mov (&DWP($bias+28,"esp"),0x54E0<<16);
&mov (&DWP($bias+32,"esp"),0xE100<<16);
&mov (&DWP($bias+36,"esp"),0xFD20<<16);
&mov (&DWP($bias+40,"esp"),0xD940<<16);
&mov (&DWP($bias+44,"esp"),0xC560<<16);
&mov (&DWP($bias+48,"esp"),0x9180<<16);
&mov (&DWP($bias+52,"esp"),0x8DA0<<16);
&mov (&DWP($bias+56,"esp"),0xA9C0<<16);
&mov (&DWP($bias+60,"esp"),0xB5E0<<16);
}
if (!$x86only) {{{
&static_label("rem_4bit");
if (!$sse2) {{ # pure-MMX "May" version...
# This code was removed since SSE2 is required for BoringSSL. The
# outer structure of the code was retained to minimize future merge
# conflicts.
}} else {{ # "June" MMX version...
# ... has slower "April" gcm_gmult_4bit_mmx with folded
# loop. This is done to conserve code size...
$S=16; # shift factor for rem_4bit
sub mmx_loop() {
# MMX version performs 2.8 times better on P4 (see comment in non-MMX
# routine for further details), 40% better on Opteron and Core2, 50%
# better on PIII... In other words effort is considered to be well
# spent...
my $inp = shift;
my $rem_4bit = shift;
my $cnt = $Zhh;
my $nhi = $Zhl;
my $nlo = $Zlh;
my $rem = $Zll;
my ($Zlo,$Zhi) = ("mm0","mm1");
my $tmp = "mm2";
&xor ($nlo,$nlo); # avoid partial register stalls on PIII
&mov ($nhi,$Zll);
&mov (&LB($nlo),&LB($nhi));
&mov ($cnt,14);
&shl (&LB($nlo),4);
&and ($nhi,0xf0);
&movq ($Zlo,&QWP(8,$Htbl,$nlo));
&movq ($Zhi,&QWP(0,$Htbl,$nlo));
&movd ($rem,$Zlo);
&jmp (&label("mmx_loop"));
&set_label("mmx_loop",16);
&psrlq ($Zlo,4);
&and ($rem,0xf);
&movq ($tmp,$Zhi);
&psrlq ($Zhi,4);
&pxor ($Zlo,&QWP(8,$Htbl,$nhi));
&mov (&LB($nlo),&BP(0,$inp,$cnt));
&psllq ($tmp,60);
&pxor ($Zhi,&QWP(0,$rem_4bit,$rem,8));
&dec ($cnt);
&movd ($rem,$Zlo);
&pxor ($Zhi,&QWP(0,$Htbl,$nhi));
&mov ($nhi,$nlo);
&pxor ($Zlo,$tmp);
&js (&label("mmx_break"));
&shl (&LB($nlo),4);
&and ($rem,0xf);
&psrlq ($Zlo,4);
&and ($nhi,0xf0);
&movq ($tmp,$Zhi);
&psrlq ($Zhi,4);
&pxor ($Zlo,&QWP(8,$Htbl,$nlo));
&psllq ($tmp,60);
&pxor ($Zhi,&QWP(0,$rem_4bit,$rem,8));
&movd ($rem,$Zlo);
&pxor ($Zhi,&QWP(0,$Htbl,$nlo));
&pxor ($Zlo,$tmp);
&jmp (&label("mmx_loop"));
&set_label("mmx_break",16);
&shl (&LB($nlo),4);
&and ($rem,0xf);
&psrlq ($Zlo,4);
&and ($nhi,0xf0);
&movq ($tmp,$Zhi);
&psrlq ($Zhi,4);
&pxor ($Zlo,&QWP(8,$Htbl,$nlo));
&psllq ($tmp,60);
&pxor ($Zhi,&QWP(0,$rem_4bit,$rem,8));
&movd ($rem,$Zlo);
&pxor ($Zhi,&QWP(0,$Htbl,$nlo));
&pxor ($Zlo,$tmp);
&psrlq ($Zlo,4);
&and ($rem,0xf);
&movq ($tmp,$Zhi);
&psrlq ($Zhi,4);
&pxor ($Zlo,&QWP(8,$Htbl,$nhi));
&psllq ($tmp,60);
&pxor ($Zhi,&QWP(0,$rem_4bit,$rem,8));
&movd ($rem,$Zlo);
&pxor ($Zhi,&QWP(0,$Htbl,$nhi));
&pxor ($Zlo,$tmp);
&psrlq ($Zlo,32); # lower part of Zlo is already there
&movd ($Zhl,$Zhi);
&psrlq ($Zhi,32);
&movd ($Zlh,$Zlo);
&movd ($Zhh,$Zhi);
&bswap ($Zll);
&bswap ($Zhl);
&bswap ($Zlh);
&bswap ($Zhh);
}
&function_begin("gcm_gmult_4bit_mmx");
&mov ($inp,&wparam(0)); # load Xi
&mov ($Htbl,&wparam(1)); # load Htable
&call (&label("pic_point"));
&set_label("pic_point");
&blindpop("eax");
&lea ("eax",&DWP(&label("rem_4bit")."-".&label("pic_point"),"eax"));
&movz ($Zll,&BP(15,$inp));
&mmx_loop($inp,"eax");
&emms ();
&mov (&DWP(12,$inp),$Zll);
&mov (&DWP(4,$inp),$Zhl);
&mov (&DWP(8,$inp),$Zlh);
&mov (&DWP(0,$inp),$Zhh);
&function_end("gcm_gmult_4bit_mmx");
######################################################################
# Below subroutine is "528B" variant of "4-bit" GCM GHASH function
# (see gcm128.c for details). It provides further 20-40% performance
# improvement over above mentioned "May" version.
&static_label("rem_8bit");
&function_begin("gcm_ghash_4bit_mmx");
{ my ($Zlo,$Zhi) = ("mm7","mm6");
my $rem_8bit = "esi";
my $Htbl = "ebx";
# parameter block
&mov ("eax",&wparam(0)); # Xi
&mov ("ebx",&wparam(1)); # Htable
&mov ("ecx",&wparam(2)); # inp
&mov ("edx",&wparam(3)); # len
&mov ("ebp","esp"); # original %esp
&call (&label("pic_point"));
&set_label ("pic_point");
&blindpop ($rem_8bit);
&lea ($rem_8bit,&DWP(&label("rem_8bit")."-".&label("pic_point"),$rem_8bit));
&sub ("esp",512+16+16); # allocate stack frame...
&and ("esp",-64); # ...and align it
&sub ("esp",16); # place for (u8)(H[]<<4)
&add ("edx","ecx"); # pointer to the end of input
&mov (&DWP(528+16+0,"esp"),"eax"); # save Xi
&mov (&DWP(528+16+8,"esp"),"edx"); # save inp+len
&mov (&DWP(528+16+12,"esp"),"ebp"); # save original %esp
{ my @lo = ("mm0","mm1","mm2");
my @hi = ("mm3","mm4","mm5");
my @tmp = ("mm6","mm7");
my ($off1,$off2,$i) = (0,0,);
&add ($Htbl,128); # optimize for size
&lea ("edi",&DWP(16+128,"esp"));
&lea ("ebp",&DWP(16+256+128,"esp"));
# decompose Htable (low and high parts are kept separately),
# generate Htable[]>>4, (u8)(Htable[]<<4), save to stack...
for ($i=0;$i<18;$i++) {
&mov ("edx",&DWP(16*$i+8-128,$Htbl)) if ($i<16);
&movq ($lo[0],&QWP(16*$i+8-128,$Htbl)) if ($i<16);
&psllq ($tmp[1],60) if ($i>1);
&movq ($hi[0],&QWP(16*$i+0-128,$Htbl)) if ($i<16);
&por ($lo[2],$tmp[1]) if ($i>1);
&movq (&QWP($off1-128,"edi"),$lo[1]) if ($i>0 && $i<17);
&psrlq ($lo[1],4) if ($i>0 && $i<17);
&movq (&QWP($off1,"edi"),$hi[1]) if ($i>0 && $i<17);
&movq ($tmp[0],$hi[1]) if ($i>0 && $i<17);
&movq (&QWP($off2-128,"ebp"),$lo[2]) if ($i>1);
&psrlq ($hi[1],4) if ($i>0 && $i<17);
&movq (&QWP($off2,"ebp"),$hi[2]) if ($i>1);
&shl ("edx",4) if ($i<16);
&mov (&BP($i,"esp"),&LB("edx")) if ($i<16);
unshift (@lo,pop(@lo)); # "rotate" registers
unshift (@hi,pop(@hi));
unshift (@tmp,pop(@tmp));
$off1 += 8 if ($i>0);
$off2 += 8 if ($i>1);
}
}
&movq ($Zhi,&QWP(0,"eax"));
&mov ("ebx",&DWP(8,"eax"));
&mov ("edx",&DWP(12,"eax")); # load Xi
&set_label("outer",16);
{ my $nlo = "eax";
my $dat = "edx";
my @nhi = ("edi","ebp");
my @rem = ("ebx","ecx");
my @red = ("mm0","mm1","mm2");
my $tmp = "mm3";
&xor ($dat,&DWP(12,"ecx")); # merge input data
&xor ("ebx",&DWP(8,"ecx"));
&pxor ($Zhi,&QWP(0,"ecx"));
&lea ("ecx",&DWP(16,"ecx")); # inp+=16
#&mov (&DWP(528+12,"esp"),$dat); # save inp^Xi
&mov (&DWP(528+8,"esp"),"ebx");
&movq (&QWP(528+0,"esp"),$Zhi);
&mov (&DWP(528+16+4,"esp"),"ecx"); # save inp
&xor ($nlo,$nlo);
&rol ($dat,8);
&mov (&LB($nlo),&LB($dat));
&mov ($nhi[1],$nlo);
&and (&LB($nlo),0x0f);
&shr ($nhi[1],4);
&pxor ($red[0],$red[0]);
&rol ($dat,8); # next byte
&pxor ($red[1],$red[1]);
&pxor ($red[2],$red[2]);
# Just like in "May" verson modulo-schedule for critical path in
# 'Z.hi ^= rem_8bit[Z.lo&0xff^((u8)H[nhi]<<4)]<<48'. Final 'pxor'
# is scheduled so late that rem_8bit[] has to be shifted *right*
# by 16, which is why last argument to pinsrw is 2, which
# corresponds to <<32=<<48>>16...
for ($j=11,$i=0;$i<15;$i++) {
if ($i>0) {
&pxor ($Zlo,&QWP(16,"esp",$nlo,8)); # Z^=H[nlo]
&rol ($dat,8); # next byte
&pxor ($Zhi,&QWP(16+128,"esp",$nlo,8));
&pxor ($Zlo,$tmp);
&pxor ($Zhi,&QWP(16+256+128,"esp",$nhi[0],8));
&xor (&LB($rem[1]),&BP(0,"esp",$nhi[0])); # rem^(H[nhi]<<4)
} else {
&movq ($Zlo,&QWP(16,"esp",$nlo,8));
&movq ($Zhi,&QWP(16+128,"esp",$nlo,8));
}
&mov (&LB($nlo),&LB($dat));
&mov ($dat,&DWP(528+$j,"esp")) if (--$j%4==0);
&movd ($rem[0],$Zlo);
&movz ($rem[1],&LB($rem[1])) if ($i>0);
&psrlq ($Zlo,8); # Z>>=8
&movq ($tmp,$Zhi);
&mov ($nhi[0],$nlo);
&psrlq ($Zhi,8);
&pxor ($Zlo,&QWP(16+256+0,"esp",$nhi[1],8)); # Z^=H[nhi]>>4
&and (&LB($nlo),0x0f);
&psllq ($tmp,56);
&pxor ($Zhi,$red[1]) if ($i>1);
&shr ($nhi[0],4);
&pinsrw ($red[0],&WP(0,$rem_8bit,$rem[1],2),2) if ($i>0);
unshift (@red,pop(@red)); # "rotate" registers
unshift (@rem,pop(@rem));
unshift (@nhi,pop(@nhi));
}
&pxor ($Zlo,&QWP(16,"esp",$nlo,8)); # Z^=H[nlo]
&pxor ($Zhi,&QWP(16+128,"esp",$nlo,8));
&xor (&LB($rem[1]),&BP(0,"esp",$nhi[0])); # rem^(H[nhi]<<4)
&pxor ($Zlo,$tmp);
&pxor ($Zhi,&QWP(16+256+128,"esp",$nhi[0],8));
&movz ($rem[1],&LB($rem[1]));
&pxor ($red[2],$red[2]); # clear 2nd word
&psllq ($red[1],4);
&movd ($rem[0],$Zlo);
&psrlq ($Zlo,4); # Z>>=4
&movq ($tmp,$Zhi);
&psrlq ($Zhi,4);
&shl ($rem[0],4); # rem<<4
&pxor ($Zlo,&QWP(16,"esp",$nhi[1],8)); # Z^=H[nhi]
&psllq ($tmp,60);
&movz ($rem[0],&LB($rem[0]));
&pxor ($Zlo,$tmp);
&pxor ($Zhi,&QWP(16+128,"esp",$nhi[1],8));
&pinsrw ($red[0],&WP(0,$rem_8bit,$rem[1],2),2);
&pxor ($Zhi,$red[1]);
&movd ($dat,$Zlo);
&pinsrw ($red[2],&WP(0,$rem_8bit,$rem[0],2),3); # last is <<48
&psllq ($red[0],12); # correct by <<16>>4
&pxor ($Zhi,$red[0]);
&psrlq ($Zlo,32);
&pxor ($Zhi,$red[2]);
&mov ("ecx",&DWP(528+16+4,"esp")); # restore inp
&movd ("ebx",$Zlo);
&movq ($tmp,$Zhi); # 01234567
&psllw ($Zhi,8); # 1.3.5.7.
&psrlw ($tmp,8); # .0.2.4.6
&por ($Zhi,$tmp); # 10325476
&bswap ($dat);
&pshufw ($Zhi,$Zhi,0b00011011); # 76543210
&bswap ("ebx");
&cmp ("ecx",&DWP(528+16+8,"esp")); # are we done?
&jne (&label("outer"));
}
&mov ("eax",&DWP(528+16+0,"esp")); # restore Xi
&mov (&DWP(12,"eax"),"edx");
&mov (&DWP(8,"eax"),"ebx");
&movq (&QWP(0,"eax"),$Zhi);
&mov ("esp",&DWP(528+16+12,"esp")); # restore original %esp
&emms ();
}
&function_end("gcm_ghash_4bit_mmx");
}}
if ($sse2) {{
######################################################################
# PCLMULQDQ version.
$Xip="eax";
$Htbl="edx";
$const="ecx";
$inp="esi";
$len="ebx";
($Xi,$Xhi)=("xmm0","xmm1"); $Hkey="xmm2";
($T1,$T2,$T3)=("xmm3","xmm4","xmm5");
($Xn,$Xhn)=("xmm6","xmm7");
&static_label("bswap");
sub clmul64x64_T2 { # minimal "register" pressure
my ($Xhi,$Xi,$Hkey,$HK)=@_;
&movdqa ($Xhi,$Xi); #
&pshufd ($T1,$Xi,0b01001110);
&pshufd ($T2,$Hkey,0b01001110) if (!defined($HK));
&pxor ($T1,$Xi); #
&pxor ($T2,$Hkey) if (!defined($HK));
$HK=$T2 if (!defined($HK));
&pclmulqdq ($Xi,$Hkey,0x00); #######
&pclmulqdq ($Xhi,$Hkey,0x11); #######
&pclmulqdq ($T1,$HK,0x00); #######
&xorps ($T1,$Xi); #
&xorps ($T1,$Xhi); #
&movdqa ($T2,$T1); #
&psrldq ($T1,8);
&pslldq ($T2,8); #
&pxor ($Xhi,$T1);
&pxor ($Xi,$T2); #
}
sub clmul64x64_T3 {
# Even though this subroutine offers visually better ILP, it
# was empirically found to be a tad slower than above version.
# At least in gcm_ghash_clmul context. But it's just as well,
# because loop modulo-scheduling is possible only thanks to
# minimized "register" pressure...
my ($Xhi,$Xi,$Hkey)=@_;
&movdqa ($T1,$Xi); #
&movdqa ($Xhi,$Xi);
&pclmulqdq ($Xi,$Hkey,0x00); #######
&pclmulqdq ($Xhi,$Hkey,0x11); #######
&pshufd ($T2,$T1,0b01001110); #
&pshufd ($T3,$Hkey,0b01001110);
&pxor ($T2,$T1); #
&pxor ($T3,$Hkey);
&pclmulqdq ($T2,$T3,0x00); #######
&pxor ($T2,$Xi); #
&pxor ($T2,$Xhi); #
&movdqa ($T3,$T2); #
&psrldq ($T2,8);
&pslldq ($T3,8); #
&pxor ($Xhi,$T2);
&pxor ($Xi,$T3); #
}
if (1) { # Algorithm 9 with <<1 twist.
# Reduction is shorter and uses only two
# temporary registers, which makes it better
# candidate for interleaving with 64x64
# multiplication. Pre-modulo-scheduled loop
# was found to be ~20% faster than Algorithm 5
# below. Algorithm 9 was therefore chosen for
# further optimization...
sub reduction_alg9 { # 17/11 times faster than Intel version
my ($Xhi,$Xi) = @_;
# 1st phase
&movdqa ($T2,$Xi); #
&movdqa ($T1,$Xi);
&psllq ($Xi,5);
&pxor ($T1,$Xi); #
&psllq ($Xi,1);
&pxor ($Xi,$T1); #
&psllq ($Xi,57); #
&movdqa ($T1,$Xi); #
&pslldq ($Xi,8);
&psrldq ($T1,8); #
&pxor ($Xi,$T2);
&pxor ($Xhi,$T1); #
# 2nd phase
&movdqa ($T2,$Xi);
&psrlq ($Xi,1);
&pxor ($Xhi,$T2); #
&pxor ($T2,$Xi);
&psrlq ($Xi,5);
&pxor ($Xi,$T2); #
&psrlq ($Xi,1); #
&pxor ($Xi,$Xhi) #
}
&function_begin_B("gcm_init_clmul");
&mov ($Htbl,&wparam(0));
&mov ($Xip,&wparam(1));
&call (&label("pic"));
&set_label("pic");
&blindpop ($const);
&lea ($const,&DWP(&label("bswap")."-".&label("pic"),$const));
&movdqu ($Hkey,&QWP(0,$Xip));
&pshufd ($Hkey,$Hkey,0b01001110);# dword swap
# <<1 twist
&pshufd ($T2,$Hkey,0b11111111); # broadcast uppermost dword
&movdqa ($T1,$Hkey);
&psllq ($Hkey,1);
&pxor ($T3,$T3); #
&psrlq ($T1,63);
&pcmpgtd ($T3,$T2); # broadcast carry bit
&pslldq ($T1,8);
&por ($Hkey,$T1); # H<<=1
# magic reduction
&pand ($T3,&QWP(16,$const)); # 0x1c2_polynomial
&pxor ($Hkey,$T3); # if(carry) H^=0x1c2_polynomial
# calculate H^2
&movdqa ($Xi,$Hkey);
&clmul64x64_T2 ($Xhi,$Xi,$Hkey);
&reduction_alg9 ($Xhi,$Xi);
&pshufd ($T1,$Hkey,0b01001110);
&pshufd ($T2,$Xi,0b01001110);
&pxor ($T1,$Hkey); # Karatsuba pre-processing
&movdqu (&QWP(0,$Htbl),$Hkey); # save H
&pxor ($T2,$Xi); # Karatsuba pre-processing
&movdqu (&QWP(16,$Htbl),$Xi); # save H^2
&palignr ($T2,$T1,8); # low part is H.lo^H.hi
&movdqu (&QWP(32,$Htbl),$T2); # save Karatsuba "salt"
&ret ();
&function_end_B("gcm_init_clmul");
&function_begin_B("gcm_gmult_clmul");
&mov ($Xip,&wparam(0));
&mov ($Htbl,&wparam(1));
&call (&label("pic"));
&set_label("pic");
&blindpop ($const);
&lea ($const,&DWP(&label("bswap")."-".&label("pic"),$const));
&movdqu ($Xi,&QWP(0,$Xip));
&movdqa ($T3,&QWP(0,$const));
&movups ($Hkey,&QWP(0,$Htbl));
&pshufb ($Xi,$T3);
&movups ($T2,&QWP(32,$Htbl));
&clmul64x64_T2 ($Xhi,$Xi,$Hkey,$T2);
&reduction_alg9 ($Xhi,$Xi);
&pshufb ($Xi,$T3);
&movdqu (&QWP(0,$Xip),$Xi);
&ret ();
&function_end_B("gcm_gmult_clmul");
&function_begin("gcm_ghash_clmul");
&mov ($Xip,&wparam(0));
&mov ($Htbl,&wparam(1));
&mov ($inp,&wparam(2));
&mov ($len,&wparam(3));
&call (&label("pic"));
&set_label("pic");
&blindpop ($const);
&lea ($const,&DWP(&label("bswap")."-".&label("pic"),$const));
&movdqu ($Xi,&QWP(0,$Xip));
&movdqa ($T3,&QWP(0,$const));
&movdqu ($Hkey,&QWP(0,$Htbl));
&pshufb ($Xi,$T3);
&sub ($len,0x10);
&jz (&label("odd_tail"));
#######
# Xi+2 =[H*(Ii+1 + Xi+1)] mod P =
# [(H*Ii+1) + (H*Xi+1)] mod P =
# [(H*Ii+1) + H^2*(Ii+Xi)] mod P
#
&movdqu ($T1,&QWP(0,$inp)); # Ii
&movdqu ($Xn,&QWP(16,$inp)); # Ii+1
&pshufb ($T1,$T3);
&pshufb ($Xn,$T3);
&movdqu ($T3,&QWP(32,$Htbl));
&pxor ($Xi,$T1); # Ii+Xi
&pshufd ($T1,$Xn,0b01001110); # H*Ii+1
&movdqa ($Xhn,$Xn);
&pxor ($T1,$Xn); #
&lea ($inp,&DWP(32,$inp)); # i+=2
&pclmulqdq ($Xn,$Hkey,0x00); #######
&pclmulqdq ($Xhn,$Hkey,0x11); #######
&pclmulqdq ($T1,$T3,0x00); #######
&movups ($Hkey,&QWP(16,$Htbl)); # load H^2
&nop ();
&sub ($len,0x20);
&jbe (&label("even_tail"));
&jmp (&label("mod_loop"));
&set_label("mod_loop",32);
&pshufd ($T2,$Xi,0b01001110); # H^2*(Ii+Xi)
&movdqa ($Xhi,$Xi);
&pxor ($T2,$Xi); #
&nop ();
&pclmulqdq ($Xi,$Hkey,0x00); #######
&pclmulqdq ($Xhi,$Hkey,0x11); #######
&pclmulqdq ($T2,$T3,0x10); #######
&movups ($Hkey,&QWP(0,$Htbl)); # load H
&xorps ($Xi,$Xn); # (H*Ii+1) + H^2*(Ii+Xi)
&movdqa ($T3,&QWP(0,$const));
&xorps ($Xhi,$Xhn);
&movdqu ($Xhn,&QWP(0,$inp)); # Ii
&pxor ($T1,$Xi); # aggregated Karatsuba post-processing
&movdqu ($Xn,&QWP(16,$inp)); # Ii+1
&pxor ($T1,$Xhi); #
&pshufb ($Xhn,$T3);
&pxor ($T2,$T1); #
&movdqa ($T1,$T2); #
&psrldq ($T2,8);
&pslldq ($T1,8); #
&pxor ($Xhi,$T2);
&pxor ($Xi,$T1); #
&pshufb ($Xn,$T3);
&pxor ($Xhi,$Xhn); # "Ii+Xi", consume early
&movdqa ($Xhn,$Xn); #&clmul64x64_TX ($Xhn,$Xn,$Hkey); H*Ii+1
&movdqa ($T2,$Xi); #&reduction_alg9($Xhi,$Xi); 1st phase
&movdqa ($T1,$Xi);
&psllq ($Xi,5);
&pxor ($T1,$Xi); #
&psllq ($Xi,1);
&pxor ($Xi,$T1); #
&pclmulqdq ($Xn,$Hkey,0x00); #######
&movups ($T3,&QWP(32,$Htbl));
&psllq ($Xi,57); #
&movdqa ($T1,$Xi); #
&pslldq ($Xi,8);
&psrldq ($T1,8); #
&pxor ($Xi,$T2);
&pxor ($Xhi,$T1); #
&pshufd ($T1,$Xhn,0b01001110);
&movdqa ($T2,$Xi); # 2nd phase
&psrlq ($Xi,1);
&pxor ($T1,$Xhn);
&pxor ($Xhi,$T2); #
&pclmulqdq ($Xhn,$Hkey,0x11); #######
&movups ($Hkey,&QWP(16,$Htbl)); # load H^2
&pxor ($T2,$Xi);
&psrlq ($Xi,5);
&pxor ($Xi,$T2); #
&psrlq ($Xi,1); #
&pxor ($Xi,$Xhi) #
&pclmulqdq ($T1,$T3,0x00); #######
&lea ($inp,&DWP(32,$inp));
&sub ($len,0x20);
&ja (&label("mod_loop"));
&set_label("even_tail");
&pshufd ($T2,$Xi,0b01001110); # H^2*(Ii+Xi)
&movdqa ($Xhi,$Xi);
&pxor ($T2,$Xi); #
&pclmulqdq ($Xi,$Hkey,0x00); #######
&pclmulqdq ($Xhi,$Hkey,0x11); #######
&pclmulqdq ($T2,$T3,0x10); #######
&movdqa ($T3,&QWP(0,$const));
&xorps ($Xi,$Xn); # (H*Ii+1) + H^2*(Ii+Xi)
&xorps ($Xhi,$Xhn);
&pxor ($T1,$Xi); # aggregated Karatsuba post-processing
&pxor ($T1,$Xhi); #
&pxor ($T2,$T1); #
&movdqa ($T1,$T2); #
&psrldq ($T2,8);
&pslldq ($T1,8); #
&pxor ($Xhi,$T2);
&pxor ($Xi,$T1); #
&reduction_alg9 ($Xhi,$Xi);
&test ($len,$len);
&jnz (&label("done"));
&movups ($Hkey,&QWP(0,$Htbl)); # load H
&set_label("odd_tail");
&movdqu ($T1,&QWP(0,$inp)); # Ii
&pshufb ($T1,$T3);
&pxor ($Xi,$T1); # Ii+Xi
&clmul64x64_T2 ($Xhi,$Xi,$Hkey); # H*(Ii+Xi)
&reduction_alg9 ($Xhi,$Xi);
&set_label("done");
&pshufb ($Xi,$T3);
&movdqu (&QWP(0,$Xip),$Xi);
&function_end("gcm_ghash_clmul");
} else { # Algorith 5. Kept for reference purposes.
sub reduction_alg5 { # 19/16 times faster than Intel version
my ($Xhi,$Xi)=@_;
# <<1
&movdqa ($T1,$Xi); #
&movdqa ($T2,$Xhi);
&pslld ($Xi,1);
&pslld ($Xhi,1); #
&psrld ($T1,31);
&psrld ($T2,31); #
&movdqa ($T3,$T1);
&pslldq ($T1,4);
&psrldq ($T3,12); #
&pslldq ($T2,4);
&por ($Xhi,$T3); #
&por ($Xi,$T1);
&por ($Xhi,$T2); #
# 1st phase
&movdqa ($T1,$Xi);
&movdqa ($T2,$Xi);
&movdqa ($T3,$Xi); #
&pslld ($T1,31);
&pslld ($T2,30);
&pslld ($Xi,25); #
&pxor ($T1,$T2);
&pxor ($T1,$Xi); #
&movdqa ($T2,$T1); #
&pslldq ($T1,12);
&psrldq ($T2,4); #
&pxor ($T3,$T1);
# 2nd phase
&pxor ($Xhi,$T3); #
&movdqa ($Xi,$T3);
&movdqa ($T1,$T3);
&psrld ($Xi,1); #
&psrld ($T1,2);
&psrld ($T3,7); #
&pxor ($Xi,$T1);
&pxor ($Xhi,$T2);
&pxor ($Xi,$T3); #
&pxor ($Xi,$Xhi); #
}
&function_begin_B("gcm_init_clmul");
&mov ($Htbl,&wparam(0));
&mov ($Xip,&wparam(1));
&call (&label("pic"));
&set_label("pic");
&blindpop ($const);
&lea ($const,&DWP(&label("bswap")."-".&label("pic"),$const));
&movdqu ($Hkey,&QWP(0,$Xip));
&pshufd ($Hkey,$Hkey,0b01001110);# dword swap
# calculate H^2
&movdqa ($Xi,$Hkey);
&clmul64x64_T3 ($Xhi,$Xi,$Hkey);
&reduction_alg5 ($Xhi,$Xi);
&movdqu (&QWP(0,$Htbl),$Hkey); # save H
&movdqu (&QWP(16,$Htbl),$Xi); # save H^2
&ret ();
&function_end_B("gcm_init_clmul");
&function_begin_B("gcm_gmult_clmul");
&mov ($Xip,&wparam(0));
&mov ($Htbl,&wparam(1));
&call (&label("pic"));
&set_label("pic");
&blindpop ($const);
&lea ($const,&DWP(&label("bswap")."-".&label("pic"),$const));
&movdqu ($Xi,&QWP(0,$Xip));
&movdqa ($Xn,&QWP(0,$const));
&movdqu ($Hkey,&QWP(0,$Htbl));
&pshufb ($Xi,$Xn);
&clmul64x64_T3 ($Xhi,$Xi,$Hkey);
&reduction_alg5 ($Xhi,$Xi);
&pshufb ($Xi,$Xn);
&movdqu (&QWP(0,$Xip),$Xi);
&ret ();
&function_end_B("gcm_gmult_clmul");
&function_begin("gcm_ghash_clmul");
&mov ($Xip,&wparam(0));
&mov ($Htbl,&wparam(1));
&mov ($inp,&wparam(2));
&mov ($len,&wparam(3));
&call (&label("pic"));
&set_label("pic");
&blindpop ($const);
&lea ($const,&DWP(&label("bswap")."-".&label("pic"),$const));
&movdqu ($Xi,&QWP(0,$Xip));
&movdqa ($T3,&QWP(0,$const));
&movdqu ($Hkey,&QWP(0,$Htbl));
&pshufb ($Xi,$T3);
&sub ($len,0x10);
&jz (&label("odd_tail"));
#######
# Xi+2 =[H*(Ii+1 + Xi+1)] mod P =
# [(H*Ii+1) + (H*Xi+1)] mod P =
# [(H*Ii+1) + H^2*(Ii+Xi)] mod P
#
&movdqu ($T1,&QWP(0,$inp)); # Ii
&movdqu ($Xn,&QWP(16,$inp)); # Ii+1
&pshufb ($T1,$T3);
&pshufb ($Xn,$T3);
&pxor ($Xi,$T1); # Ii+Xi
&clmul64x64_T3 ($Xhn,$Xn,$Hkey); # H*Ii+1
&movdqu ($Hkey,&QWP(16,$Htbl)); # load H^2
&sub ($len,0x20);
&lea ($inp,&DWP(32,$inp)); # i+=2
&jbe (&label("even_tail"));
&set_label("mod_loop");
&clmul64x64_T3 ($Xhi,$Xi,$Hkey); # H^2*(Ii+Xi)
&movdqu ($Hkey,&QWP(0,$Htbl)); # load H
&pxor ($Xi,$Xn); # (H*Ii+1) + H^2*(Ii+Xi)
&pxor ($Xhi,$Xhn);
&reduction_alg5 ($Xhi,$Xi);
#######
&movdqa ($T3,&QWP(0,$const));
&movdqu ($T1,&QWP(0,$inp)); # Ii
&movdqu ($Xn,&QWP(16,$inp)); # Ii+1
&pshufb ($T1,$T3);
&pshufb ($Xn,$T3);
&pxor ($Xi,$T1); # Ii+Xi
&clmul64x64_T3 ($Xhn,$Xn,$Hkey); # H*Ii+1
&movdqu ($Hkey,&QWP(16,$Htbl)); # load H^2
&sub ($len,0x20);
&lea ($inp,&DWP(32,$inp));
&ja (&label("mod_loop"));
&set_label("even_tail");
&clmul64x64_T3 ($Xhi,$Xi,$Hkey); # H^2*(Ii+Xi)
&pxor ($Xi,$Xn); # (H*Ii+1) + H^2*(Ii+Xi)
&pxor ($Xhi,$Xhn);
&reduction_alg5 ($Xhi,$Xi);
&movdqa ($T3,&QWP(0,$const));
&test ($len,$len);
&jnz (&label("done"));
&movdqu ($Hkey,&QWP(0,$Htbl)); # load H
&set_label("odd_tail");
&movdqu ($T1,&QWP(0,$inp)); # Ii
&pshufb ($T1,$T3);
&pxor ($Xi,$T1); # Ii+Xi
&clmul64x64_T3 ($Xhi,$Xi,$Hkey); # H*(Ii+Xi)
&reduction_alg5 ($Xhi,$Xi);
&movdqa ($T3,&QWP(0,$const));
&set_label("done");
&pshufb ($Xi,$T3);
&movdqu (&QWP(0,$Xip),$Xi);
&function_end("gcm_ghash_clmul");
}
&set_label("bswap",64);
&data_byte(15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0);
&data_byte(1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0xc2); # 0x1c2_polynomial
&set_label("rem_8bit",64);
&data_short(0x0000,0x01C2,0x0384,0x0246,0x0708,0x06CA,0x048C,0x054E);
&data_short(0x0E10,0x0FD2,0x0D94,0x0C56,0x0918,0x08DA,0x0A9C,0x0B5E);
&data_short(0x1C20,0x1DE2,0x1FA4,0x1E66,0x1B28,0x1AEA,0x18AC,0x196E);
&data_short(0x1230,0x13F2,0x11B4,0x1076,0x1538,0x14FA,0x16BC,0x177E);
&data_short(0x3840,0x3982,0x3BC4,0x3A06,0x3F48,0x3E8A,0x3CCC,0x3D0E);
&data_short(0x3650,0x3792,0x35D4,0x3416,0x3158,0x309A,0x32DC,0x331E);
&data_short(0x2460,0x25A2,0x27E4,0x2626,0x2368,0x22AA,0x20EC,0x212E);
&data_short(0x2A70,0x2BB2,0x29F4,0x2836,0x2D78,0x2CBA,0x2EFC,0x2F3E);
&data_short(0x7080,0x7142,0x7304,0x72C6,0x7788,0x764A,0x740C,0x75CE);
&data_short(0x7E90,0x7F52,0x7D14,0x7CD6,0x7998,0x785A,0x7A1C,0x7BDE);
&data_short(0x6CA0,0x6D62,0x6F24,0x6EE6,0x6BA8,0x6A6A,0x682C,0x69EE);
&data_short(0x62B0,0x6372,0x6134,0x60F6,0x65B8,0x647A,0x663C,0x67FE);
&data_short(0x48C0,0x4902,0x4B44,0x4A86,0x4FC8,0x4E0A,0x4C4C,0x4D8E);
&data_short(0x46D0,0x4712,0x4554,0x4496,0x41D8,0x401A,0x425C,0x439E);
&data_short(0x54E0,0x5522,0x5764,0x56A6,0x53E8,0x522A,0x506C,0x51AE);
&data_short(0x5AF0,0x5B32,0x5974,0x58B6,0x5DF8,0x5C3A,0x5E7C,0x5FBE);
&data_short(0xE100,0xE0C2,0xE284,0xE346,0xE608,0xE7CA,0xE58C,0xE44E);
&data_short(0xEF10,0xEED2,0xEC94,0xED56,0xE818,0xE9DA,0xEB9C,0xEA5E);
&data_short(0xFD20,0xFCE2,0xFEA4,0xFF66,0xFA28,0xFBEA,0xF9AC,0xF86E);
&data_short(0xF330,0xF2F2,0xF0B4,0xF176,0xF438,0xF5FA,0xF7BC,0xF67E);
&data_short(0xD940,0xD882,0xDAC4,0xDB06,0xDE48,0xDF8A,0xDDCC,0xDC0E);
&data_short(0xD750,0xD692,0xD4D4,0xD516,0xD058,0xD19A,0xD3DC,0xD21E);
&data_short(0xC560,0xC4A2,0xC6E4,0xC726,0xC268,0xC3AA,0xC1EC,0xC02E);
&data_short(0xCB70,0xCAB2,0xC8F4,0xC936,0xCC78,0xCDBA,0xCFFC,0xCE3E);
&data_short(0x9180,0x9042,0x9204,0x93C6,0x9688,0x974A,0x950C,0x94CE);
&data_short(0x9F90,0x9E52,0x9C14,0x9DD6,0x9898,0x995A,0x9B1C,0x9ADE);
&data_short(0x8DA0,0x8C62,0x8E24,0x8FE6,0x8AA8,0x8B6A,0x892C,0x88EE);
&data_short(0x83B0,0x8272,0x8034,0x81F6,0x84B8,0x857A,0x873C,0x86FE);
&data_short(0xA9C0,0xA802,0xAA44,0xAB86,0xAEC8,0xAF0A,0xAD4C,0xAC8E);
&data_short(0xA7D0,0xA612,0xA454,0xA596,0xA0D8,0xA11A,0xA35C,0xA29E);
&data_short(0xB5E0,0xB422,0xB664,0xB7A6,0xB2E8,0xB32A,0xB16C,0xB0AE);
&data_short(0xBBF0,0xBA32,0xB874,0xB9B6,0xBCF8,0xBD3A,0xBF7C,0xBEBE);
}} # $sse2
&set_label("rem_4bit",64);
&data_word(0,0x0000<<$S,0,0x1C20<<$S,0,0x3840<<$S,0,0x2460<<$S);
&data_word(0,0x7080<<$S,0,0x6CA0<<$S,0,0x48C0<<$S,0,0x54E0<<$S);
&data_word(0,0xE100<<$S,0,0xFD20<<$S,0,0xD940<<$S,0,0xC560<<$S);
&data_word(0,0x9180<<$S,0,0x8DA0<<$S,0,0xA9C0<<$S,0,0xB5E0<<$S);
}}} # !$x86only
&asciz("GHASH for x86, CRYPTOGAMS by <appro\@openssl.org>");
&asm_finish();
close STDOUT;
# A question was risen about choice of vanilla MMX. Or rather why wasn't
# SSE2 chosen instead? In addition to the fact that MMX runs on legacy
# CPUs such as PIII, "4-bit" MMX version was observed to provide better
# performance than *corresponding* SSE2 one even on contemporary CPUs.
# SSE2 results were provided by Peter-Michael Hager. He maintains SSE2
# implementation featuring full range of lookup-table sizes, but with
# per-invocation lookup table setup. Latter means that table size is
# chosen depending on how much data is to be hashed in every given call,
# more data - larger table. Best reported result for Core2 is ~4 cycles
# per processed byte out of 64KB block. This number accounts even for
# 64KB table setup overhead. As discussed in gcm128.c we choose to be
# more conservative in respect to lookup table sizes, but how do the
# results compare? Minimalistic "256B" MMX version delivers ~11 cycles
# on same platform. As also discussed in gcm128.c, next in line "8-bit
# Shoup's" or "4KB" method should deliver twice the performance of
# "256B" one, in other words not worse than ~6 cycles per byte. It
# should be also be noted that in SSE2 case improvement can be "super-
# linear," i.e. more than twice, mostly because >>8 maps to single
# instruction on SSE2 register. This is unlike "4-bit" case when >>4
# maps to same amount of instructions in both MMX and SSE2 cases.
# Bottom line is that switch to SSE2 is considered to be justifiable
# only in case we choose to implement "8-bit" method...
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