crypto/fipsmodule/modes/asm/ghash-ssse3-x86_64.pl - boringssl - Git at Google

 #!/usr/bin/env perl
 # Copyright (c) 2019, Google Inc.
 #
 # Permission to use, copy, modify, and/or distribute this software for any
 # purpose with or without fee is hereby granted, provided that the above
 # copyright notice and this permission notice appear in all copies.
 #
 # THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 # SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 # OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 # CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

 # ghash-ssse3-x86_64.pl is a constant-time variant of the traditional 4-bit
 # table-based GHASH implementation. It requires SSSE3 instructions.
 #
 # For background, the table-based strategy is a 4-bit windowed multiplication.
 # It precomputes all 4-bit multiples of H (this is 16 128-bit rows), then loops
 # over 4-bit windows of the input and indexes them up into the table. Visually,
 # it multiplies as in the schoolbook multiplication diagram below, but with
 # more terms. (Each term is 4 bits, so there are 32 terms in each row.) First
 # it incorporates the terms labeled '1' by indexing the most significant term
 # of X into the table. Then it shifts and repeats for '2' and so on.
 #
 #        hhhhhh
 #  *     xxxxxx
 #  ============
 #        666666
 #       555555
 #      444444
 #     333333
 #    222222
 #   111111
 #
 # This implementation changes the order. We treat the table as a 16×16 matrix
 # and transpose it. The first row is then the first byte of each multiple of H,
 # and so on. We then reorder terms as below. Observe that the terms labeled '1'
 # and '2' are all lookups into the first row, etc. This maps well to the SSSE3
 # pshufb instruction, using alternating terms of X in parallel as indices. This
 # alternation is needed because pshufb maps 4 bits to 8 bits. Then we shift and
 # repeat for each row.
 #
 #        hhhhhh
 #  *     xxxxxx
 #  ============
 #        224466
 #       113355
 #      224466
 #     113355
 #    224466
 #   113355
 #
 # Next we account for GCM's confusing bit order. The "first" bit is the least
 # significant coefficient, but GCM treats the most sigificant bit within a byte
 # as first. Bytes are little-endian, and bits are big-endian. We reverse the
 # bytes in XMM registers for a consistent bit and byte ordering, but this means
 # the least significant bit is the most significant coefficient and vice versa.
 #
 # For consistency, "low", "high", "left-shift", and "right-shift" refer to the
 # bit ordering within the XMM register, rather than the reversed coefficient
 # ordering. Low bits are less significant bits and more significant
 # coefficients. Right-shifts move from MSB to the LSB and correspond to
 # increasing the power of each coefficient.
 #
 # Note this bit reversal enters into the table's column indices. H*1 is stored
 # in column 0b1000 and H*x^3 is stored in column 0b0001. It also means earlier
 # table rows contain more significant coefficients, so we iterate forwards.

 use strict;

 my $flavour = shift;
 my $output  = shift;
 if ($flavour =~ /\./) { $output = $flavour; undef $flavour; }

 my $win64 = 0;
 $win64 = 1 if ($flavour =~ /[nm]asm|mingw64/ || $output =~ /\.asm$/);

 $0 =~ m/(.*[\/\\])[^\/\\]+$/;
 my $dir = $1;
 my $xlate;
 ( $xlate="${dir}x86_64-xlate.pl" and -f $xlate ) or
 ( $xlate="${dir}../../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";

 open OUT, "| \"$^X\" \"$xlate\" $flavour \"$output\"";
 *STDOUT = *OUT;

 my ($Xi, $Htable, $in, $len) = $win64 ? ("%rcx", "%rdx", "%r8", "%r9") :
                                         ("%rdi", "%rsi", "%rdx", "%rcx");


 my $code = <<____;
 .text

 # gcm_gmult_ssse3 multiplies |Xi| by |Htable| and writes the result to |Xi|.
 # |Xi| is represented in GHASH's serialized byte representation. |Htable| is
 # formatted as described above.
 # void gcm_gmult_ssse3(uint64_t Xi[2], const u128 Htable[16]);
 .type	gcm_gmult_ssse3, \@abi-omnipotent
 .globl	gcm_gmult_ssse3
 .align	16
 gcm_gmult_ssse3:
 .cfi_startproc
 .seh_startproc
 	_CET_ENDBR
 ____
 $code .= <<____ if ($win64);
 	subq	\$40, %rsp
 .seh_stackalloc	40
 	movdqa	%xmm6, (%rsp)
 .seh_savexmm	%xmm6, 0
 	movdqa	%xmm10, 16(%rsp)
 .seh_savexmm	%xmm10, 16
 .seh_endprologue
 ____
 $code .= <<____;
 	movdqu	($Xi), %xmm0
 	movdqa	.Lreverse_bytes(%rip), %xmm10
 	movdqa	.Llow4_mask(%rip), %xmm2

 	# Reverse input bytes to deserialize.
 	pshufb	%xmm10, %xmm0

 	# Split each byte into low (%xmm0) and high (%xmm1) halves.
 	movdqa	%xmm2, %xmm1
 	pandn	%xmm0, %xmm1
 	psrld	\$4, %xmm1
 	pand	%xmm2, %xmm0

 	# Maintain the result in %xmm2 (the value) and %xmm3 (carry bits). Note
 	# that, due to bit reversal, %xmm3 contains bits that fall off when
 	# right-shifting, not left-shifting.
 	pxor	%xmm2, %xmm2
 	pxor	%xmm3, %xmm3
 ____

 my $call_counter = 0;
 # process_rows returns assembly code to process $rows rows of the table. On
 # input, $Htable stores the pointer to the next row. %xmm0 and %xmm1 store the
 # low and high halves of the input. The result so far is passed in %xmm2. %xmm3
 # must be zero. On output, $Htable is advanced to the next row and %xmm2 is
 # updated. %xmm3 remains zero. It clobbers %rax, %xmm4, %xmm5, and %xmm6.
 sub process_rows {
     my ($rows) = @_;
     $call_counter++;

     # Shifting whole XMM registers by bits is complex. psrldq shifts by bytes,
     # and psrlq shifts the two 64-bit halves separately. Each row produces 8
     # bits of carry, and the reduction needs an additional 7-bit shift. This
     # must fit in 64 bits so reduction can use psrlq. This allows up to 7 rows
     # at a time.
     die "Carry register would overflow 64 bits." if ($rows*8 + 7 > 64);

     return <<____;
 	movq	\$$rows, %rax
 .Loop_row_$call_counter:
 	movdqa	($Htable), %xmm4
 	leaq	16($Htable), $Htable

 	# Right-shift %xmm2 and %xmm3 by 8 bytes.
 	movdqa	%xmm2, %xmm6
 	palignr	\$1, %xmm3, %xmm6
 	movdqa	%xmm6, %xmm3
 	psrldq	\$1, %xmm2

 	# Load the next table row and index the low and high bits of the input.
 	# Note the low (respectively, high) half corresponds to more
 	# (respectively, less) significant coefficients.
 	movdqa	%xmm4, %xmm5
 	pshufb	%xmm0, %xmm4
 	pshufb	%xmm1, %xmm5

 	# Add the high half (%xmm5) without shifting.
 	pxor	%xmm5, %xmm2

 	# Add the low half (%xmm4). This must be right-shifted by 4 bits. First,
 	# add into the carry register (%xmm3).
 	movdqa	%xmm4, %xmm5
 	psllq	\$60, %xmm5
 	movdqa	%xmm5, %xmm6
 	pslldq	\$8, %xmm6
 	pxor	%xmm6, %xmm3

 	# Next, add into %xmm2.
 	psrldq	\$8, %xmm5
 	pxor	%xmm5, %xmm2
 	psrlq	\$4, %xmm4
 	pxor	%xmm4, %xmm2

 	subq	\$1, %rax
 	jnz	.Loop_row_$call_counter

 	# Reduce the carry register. The reduction polynomial is 1 + x + x^2 +
 	# x^7, so we shift and XOR four times.
 	pxor	%xmm3, %xmm2	# x^0 = 0
 	psrlq	\$1, %xmm3
 	pxor	%xmm3, %xmm2	# x^1 = x
 	psrlq	\$1, %xmm3
 	pxor	%xmm3, %xmm2	# x^(1+1) = x^2
 	psrlq	\$5, %xmm3
 	pxor	%xmm3, %xmm2	# x^(1+1+5) = x^7
 	pxor	%xmm3, %xmm3
 ____
 }

 # We must reduce at least once every 7 rows, so divide into three chunks.
 $code .= process_rows(5);
 $code .= process_rows(5);
 $code .= process_rows(6);

 $code .= <<____;
 	# Store the result. Reverse bytes to serialize.
 	pshufb	%xmm10, %xmm2
 	movdqu	%xmm2, ($Xi)

 	# Zero any registers which contain secrets.
 	pxor	%xmm0, %xmm0
 	pxor	%xmm1, %xmm1
 	pxor	%xmm2, %xmm2
 	pxor	%xmm3, %xmm3
 	pxor	%xmm4, %xmm4
 	pxor	%xmm5, %xmm5
 	pxor	%xmm6, %xmm6
 ____
 $code .= <<____ if ($win64);
 	movdqa	(%rsp), %xmm6
 	movdqa	16(%rsp), %xmm10
 	addq	\$40, %rsp
 ____
 $code .= <<____;
 	ret
 .cfi_endproc
 .seh_endproc
 .size	gcm_gmult_ssse3,.-gcm_gmult_ssse3
 ____

 $code .= <<____;
 # gcm_ghash_ssse3 incorporates |len| bytes from |in| to |Xi|, using |Htable| as
 # the key. It writes the result back to |Xi|. |Xi| is represented in GHASH's
 # serialized byte representation. |Htable| is formatted as described above.
 # void gcm_ghash_ssse3(uint64_t Xi[2], const u128 Htable[16], const uint8_t *in,
 #                      size_t len);
 .type	gcm_ghash_ssse3, \@abi-omnipotent
 .globl	gcm_ghash_ssse3
 .align	16
 gcm_ghash_ssse3:
 .cfi_startproc
 .seh_startproc
 	_CET_ENDBR
 ____
 $code .= <<____ if ($win64);
 	subq	\$56, %rsp
 .seh_stackalloc	56
 	movdqa	%xmm6, (%rsp)
 .seh_savexmm	%xmm6, 0
 	movdqa	%xmm10, 16(%rsp)
 .seh_savexmm	%xmm10, 16
 	movdqa	%xmm11, 32(%rsp)
 .seh_savexmm	%xmm11, 32
 .seh_endprologue
 ____
 $code .= <<____;
 	movdqu	($Xi), %xmm0
 	movdqa	.Lreverse_bytes(%rip), %xmm10
 	movdqa	.Llow4_mask(%rip), %xmm11

 	# This function only processes whole blocks.
 	andq	\$-16, $len

 	# Reverse input bytes to deserialize. We maintain the running
 	# total in %xmm0.
 	pshufb	%xmm10, %xmm0

 	# Iterate over each block. On entry to each iteration, %xmm3 is zero.
 	pxor	%xmm3, %xmm3
 .Loop_ghash:
 	# Incorporate the next block of input.
 	movdqu	($in), %xmm1
 	pshufb	%xmm10, %xmm1	# Reverse bytes.
 	pxor	%xmm1, %xmm0

 	# Split each byte into low (%xmm0) and high (%xmm1) halves.
 	movdqa	%xmm11, %xmm1
 	pandn	%xmm0, %xmm1
 	psrld	\$4, %xmm1
 	pand	%xmm11, %xmm0

 	# Maintain the result in %xmm2 (the value) and %xmm3 (carry bits). Note
 	# that, due to bit reversal, %xmm3 contains bits that fall off when
 	# right-shifting, not left-shifting.
 	pxor	%xmm2, %xmm2
 	# %xmm3 is already zero at this point.
 ____

 # We must reduce at least once every 7 rows, so divide into three chunks.
 $code .= process_rows(5);
 $code .= process_rows(5);
 $code .= process_rows(6);

 $code .= <<____;
 	movdqa	%xmm2, %xmm0

 	# Rewind $Htable for the next iteration.
 	leaq	-256($Htable), $Htable

 	# Advance input and continue.
 	leaq	16($in), $in
 	subq	\$16, $len
 	jnz	.Loop_ghash

 	# Reverse bytes and store the result.
 	pshufb	%xmm10, %xmm0
 	movdqu	%xmm0, ($Xi)

 	# Zero any registers which contain secrets.
 	pxor	%xmm0, %xmm0
 	pxor	%xmm1, %xmm1
 	pxor	%xmm2, %xmm2
 	pxor	%xmm3, %xmm3
 	pxor	%xmm4, %xmm4
 	pxor	%xmm5, %xmm5
 	pxor	%xmm6, %xmm6
 ____
 $code .= <<____ if ($win64);
 	movdqa	(%rsp), %xmm6
 	movdqa	16(%rsp), %xmm10
 	movdqa	32(%rsp), %xmm11
 	addq	\$56, %rsp
 ____
 $code .= <<____;
 	ret
 .cfi_endproc
 .seh_endproc
 .size	gcm_ghash_ssse3,.-gcm_ghash_ssse3

 .section .rodata
 .align	16
 # .Lreverse_bytes is a permutation which, if applied with pshufb, reverses the
 # bytes in an XMM register.
 .Lreverse_bytes:
 .byte	15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
 # .Llow4_mask is an XMM mask which selects the low four bits of each byte.
 .Llow4_mask:
 .quad	0x0f0f0f0f0f0f0f0f, 0x0f0f0f0f0f0f0f0f
 .text
 ____

 print $code;
 close STDOUT or die "error closing STDOUT: $!";
	#!/usr/bin/env perl
	# Copyright (c) 2019, Google Inc.
	#
	# Permission to use, copy, modify, and/or distribute this software for any
	# purpose with or without fee is hereby granted, provided that the above
	# copyright notice and this permission notice appear in all copies.
	#
	# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
	# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
	# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
	# SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
	# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
	# OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
	# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

	# ghash-ssse3-x86_64.pl is a constant-time variant of the traditional 4-bit
	# table-based GHASH implementation. It requires SSSE3 instructions.
	#
	# For background, the table-based strategy is a 4-bit windowed multiplication.
	# It precomputes all 4-bit multiples of H (this is 16 128-bit rows), then loops
	# over 4-bit windows of the input and indexes them up into the table. Visually,
	# it multiplies as in the schoolbook multiplication diagram below, but with
	# more terms. (Each term is 4 bits, so there are 32 terms in each row.) First
	# it incorporates the terms labeled '1' by indexing the most significant term
	# of X into the table. Then it shifts and repeats for '2' and so on.
	#
	# hhhhhh
	# * xxxxxx
	# ============
	# 666666
	# 555555
	# 444444
	# 333333
	# 222222
	# 111111
	#
	# This implementation changes the order. We treat the table as a 16×16 matrix
	# and transpose it. The first row is then the first byte of each multiple of H,
	# and so on. We then reorder terms as below. Observe that the terms labeled '1'
	# and '2' are all lookups into the first row, etc. This maps well to the SSSE3
	# pshufb instruction, using alternating terms of X in parallel as indices. This
	# alternation is needed because pshufb maps 4 bits to 8 bits. Then we shift and
	# repeat for each row.
	#
	# hhhhhh
	# * xxxxxx
	# ============
	# 224466
	# 113355
	# 224466
	# 113355
	# 224466
	# 113355
	#
	# Next we account for GCM's confusing bit order. The "first" bit is the least
	# significant coefficient, but GCM treats the most sigificant bit within a byte
	# as first. Bytes are little-endian, and bits are big-endian. We reverse the
	# bytes in XMM registers for a consistent bit and byte ordering, but this means
	# the least significant bit is the most significant coefficient and vice versa.
	#
	# For consistency, "low", "high", "left-shift", and "right-shift" refer to the
	# bit ordering within the XMM register, rather than the reversed coefficient
	# ordering. Low bits are less significant bits and more significant
	# coefficients. Right-shifts move from MSB to the LSB and correspond to
	# increasing the power of each coefficient.
	#
	# Note this bit reversal enters into the table's column indices. H*1 is stored
	# in column 0b1000 and H*x^3 is stored in column 0b0001. It also means earlier
	# table rows contain more significant coefficients, so we iterate forwards.

	use strict;

	my $flavour = shift;
	my $output = shift;
	if ($flavour =~ /\./) { $output = $flavour; undef $flavour; }

	my $win64 = 0;
	$win64 = 1 if ($flavour =~ /[nm]asm\|mingw64/ \|\| $output =~ /\.asm$/);

	$0 =~ m/(.*[\/\\])[^\/\\]+$/;
	my $dir = $1;
	my $xlate;
	( $xlate="${dir}x86_64-xlate.pl" and -f $xlate ) or
	( $xlate="${dir}../../../perlasm/x86_64-xlate.pl" and -f $xlate) or
	die "can't locate x86_64-xlate.pl";

	open OUT, "\| \"$^X\" \"$xlate\" $flavour \"$output\"";
	STDOUT = OUT;

	my ($Xi, $Htable, $in, $len) = $win64 ? ("%rcx", "%rdx", "%r8", "%r9") :
	("%rdi", "%rsi", "%rdx", "%rcx");


	my $code = <<____;
	.text

	# gcm_gmult_ssse3 multiplies \|Xi\| by \|Htable\| and writes the result to \|Xi\|.
	# \|Xi\| is represented in GHASH's serialized byte representation. \|Htable\| is
	# formatted as described above.
	# void gcm_gmult_ssse3(uint64_t Xi[2], const u128 Htable[16]);
	.type gcm_gmult_ssse3, \@abi-omnipotent
	.globl gcm_gmult_ssse3
	.align 16
	gcm_gmult_ssse3:
	.cfi_startproc
	.seh_startproc
	_CET_ENDBR
	____
	$code .= <<____ if ($win64);
	subq \$40, %rsp
	.seh_stackalloc 40
	movdqa %xmm6, (%rsp)
	.seh_savexmm %xmm6, 0
	movdqa %xmm10, 16(%rsp)
	.seh_savexmm %xmm10, 16
	.seh_endprologue
	____
	$code .= <<____;
	movdqu ($Xi), %xmm0
	movdqa .Lreverse_bytes(%rip), %xmm10
	movdqa .Llow4_mask(%rip), %xmm2

	# Reverse input bytes to deserialize.
	pshufb %xmm10, %xmm0

	# Split each byte into low (%xmm0) and high (%xmm1) halves.
	movdqa %xmm2, %xmm1
	pandn %xmm0, %xmm1
	psrld \$4, %xmm1
	pand %xmm2, %xmm0

	# Maintain the result in %xmm2 (the value) and %xmm3 (carry bits). Note
	# that, due to bit reversal, %xmm3 contains bits that fall off when
	# right-shifting, not left-shifting.
	pxor %xmm2, %xmm2
	pxor %xmm3, %xmm3
	____

	my $call_counter = 0;
	# process_rows returns assembly code to process $rows rows of the table. On
	# input, $Htable stores the pointer to the next row. %xmm0 and %xmm1 store the
	# low and high halves of the input. The result so far is passed in %xmm2. %xmm3
	# must be zero. On output, $Htable is advanced to the next row and %xmm2 is
	# updated. %xmm3 remains zero. It clobbers %rax, %xmm4, %xmm5, and %xmm6.
	sub process_rows {
	my ($rows) = @_;
	$call_counter++;

	# Shifting whole XMM registers by bits is complex. psrldq shifts by bytes,
	# and psrlq shifts the two 64-bit halves separately. Each row produces 8
	# bits of carry, and the reduction needs an additional 7-bit shift. This
	# must fit in 64 bits so reduction can use psrlq. This allows up to 7 rows
	# at a time.
	die "Carry register would overflow 64 bits." if ($rows*8 + 7 > 64);

	return <<____;
	movq \$$rows, %rax
	.Loop_row_$call_counter:
	movdqa ($Htable), %xmm4
	leaq 16($Htable), $Htable

	# Right-shift %xmm2 and %xmm3 by 8 bytes.
	movdqa %xmm2, %xmm6
	palignr \$1, %xmm3, %xmm6
	movdqa %xmm6, %xmm3
	psrldq \$1, %xmm2

	# Load the next table row and index the low and high bits of the input.
	# Note the low (respectively, high) half corresponds to more
	# (respectively, less) significant coefficients.
	movdqa %xmm4, %xmm5
	pshufb %xmm0, %xmm4
	pshufb %xmm1, %xmm5

	# Add the high half (%xmm5) without shifting.
	pxor %xmm5, %xmm2

	# Add the low half (%xmm4). This must be right-shifted by 4 bits. First,
	# add into the carry register (%xmm3).
	movdqa %xmm4, %xmm5
	psllq \$60, %xmm5
	movdqa %xmm5, %xmm6
	pslldq \$8, %xmm6
	pxor %xmm6, %xmm3

	# Next, add into %xmm2.
	psrldq \$8, %xmm5
	pxor %xmm5, %xmm2
	psrlq \$4, %xmm4
	pxor %xmm4, %xmm2

	subq \$1, %rax
	jnz .Loop_row_$call_counter

	# Reduce the carry register. The reduction polynomial is 1 + x + x^2 +
	# x^7, so we shift and XOR four times.
	pxor %xmm3, %xmm2 # x^0 = 0
	psrlq \$1, %xmm3
	pxor %xmm3, %xmm2 # x^1 = x
	psrlq \$1, %xmm3
	pxor %xmm3, %xmm2 # x^(1+1) = x^2
	psrlq \$5, %xmm3
	pxor %xmm3, %xmm2 # x^(1+1+5) = x^7
	pxor %xmm3, %xmm3
	____
	}

	# We must reduce at least once every 7 rows, so divide into three chunks.
	$code .= process_rows(5);
	$code .= process_rows(5);
	$code .= process_rows(6);

	$code .= <<____;
	# Store the result. Reverse bytes to serialize.
	pshufb %xmm10, %xmm2
	movdqu %xmm2, ($Xi)

	# Zero any registers which contain secrets.
	pxor %xmm0, %xmm0
	pxor %xmm1, %xmm1
	pxor %xmm2, %xmm2
	pxor %xmm3, %xmm3
	pxor %xmm4, %xmm4
	pxor %xmm5, %xmm5
	pxor %xmm6, %xmm6
	____
	$code .= <<____ if ($win64);
	movdqa (%rsp), %xmm6
	movdqa 16(%rsp), %xmm10
	addq \$40, %rsp
	____
	$code .= <<____;
	ret
	.cfi_endproc
	.seh_endproc
	.size gcm_gmult_ssse3,.-gcm_gmult_ssse3
	____

	$code .= <<____;
	# gcm_ghash_ssse3 incorporates \|len\| bytes from \|in\| to \|Xi\|, using \|Htable\| as
	# the key. It writes the result back to \|Xi\|. \|Xi\| is represented in GHASH's
	# serialized byte representation. \|Htable\| is formatted as described above.
	# void gcm_ghash_ssse3(uint64_t Xi[2], const u128 Htable[16], const uint8_t *in,
	# size_t len);
	.type gcm_ghash_ssse3, \@abi-omnipotent
	.globl gcm_ghash_ssse3
	.align 16
	gcm_ghash_ssse3:
	.cfi_startproc
	.seh_startproc
	_CET_ENDBR
	____
	$code .= <<____ if ($win64);
	subq \$56, %rsp
	.seh_stackalloc 56
	movdqa %xmm6, (%rsp)
	.seh_savexmm %xmm6, 0
	movdqa %xmm10, 16(%rsp)
	.seh_savexmm %xmm10, 16
	movdqa %xmm11, 32(%rsp)
	.seh_savexmm %xmm11, 32
	.seh_endprologue
	____
	$code .= <<____;
	movdqu ($Xi), %xmm0
	movdqa .Lreverse_bytes(%rip), %xmm10
	movdqa .Llow4_mask(%rip), %xmm11

	# This function only processes whole blocks.
	andq \$-16, $len

	# Reverse input bytes to deserialize. We maintain the running
	# total in %xmm0.
	pshufb %xmm10, %xmm0

	# Iterate over each block. On entry to each iteration, %xmm3 is zero.
	pxor %xmm3, %xmm3
	.Loop_ghash:
	# Incorporate the next block of input.
	movdqu ($in), %xmm1
	pshufb %xmm10, %xmm1 # Reverse bytes.
	pxor %xmm1, %xmm0

	# Split each byte into low (%xmm0) and high (%xmm1) halves.
	movdqa %xmm11, %xmm1
	pandn %xmm0, %xmm1
	psrld \$4, %xmm1
	pand %xmm11, %xmm0

	# Maintain the result in %xmm2 (the value) and %xmm3 (carry bits). Note
	# that, due to bit reversal, %xmm3 contains bits that fall off when
	# right-shifting, not left-shifting.
	pxor %xmm2, %xmm2
	# %xmm3 is already zero at this point.
	____

	# We must reduce at least once every 7 rows, so divide into three chunks.
	$code .= process_rows(5);
	$code .= process_rows(5);
	$code .= process_rows(6);

	$code .= <<____;
	movdqa %xmm2, %xmm0

	# Rewind $Htable for the next iteration.
	leaq -256($Htable), $Htable

	# Advance input and continue.
	leaq 16($in), $in
	subq \$16, $len
	jnz .Loop_ghash

	# Reverse bytes and store the result.
	pshufb %xmm10, %xmm0
	movdqu %xmm0, ($Xi)

	# Zero any registers which contain secrets.
	pxor %xmm0, %xmm0
	pxor %xmm1, %xmm1
	pxor %xmm2, %xmm2
	pxor %xmm3, %xmm3
	pxor %xmm4, %xmm4
	pxor %xmm5, %xmm5
	pxor %xmm6, %xmm6
	____
	$code .= <<____ if ($win64);
	movdqa (%rsp), %xmm6
	movdqa 16(%rsp), %xmm10
	movdqa 32(%rsp), %xmm11
	addq \$56, %rsp
	____
	$code .= <<____;
	ret
	.cfi_endproc
	.seh_endproc
	.size gcm_ghash_ssse3,.-gcm_ghash_ssse3

	.section .rodata
	.align 16
	# .Lreverse_bytes is a permutation which, if applied with pshufb, reverses the
	# bytes in an XMM register.
	.Lreverse_bytes:
	.byte 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
	# .Llow4_mask is an XMM mask which selects the low four bits of each byte.
	.Llow4_mask:
	.quad 0x0f0f0f0f0f0f0f0f, 0x0f0f0f0f0f0f0f0f
	.text
	____

	print $code;
	close STDOUT or die "error closing STDOUT: $!";