liblzma: Add lzma_memcmplen() for fast memory comparison.

This commit just adds the function. Its uses will be in
separate commits.

This hasn't been tested much yet and it's perhaps a bit early
to commit it but if there are bugs they should get found quite
quickly.

Thanks to Jun I Jin from Intel for help and for pointing out
that string comparison needs to be optimized in liblzma.
This commit is contained in:
Lasse Collin 2014-07-25 20:57:20 +03:00
parent 765735cf52
commit e1c8f1d01f
3 changed files with 184 additions and 0 deletions

View File

@ -560,6 +560,7 @@ echo "Initializing gettext:"
AM_GNU_GETTEXT_VERSION([0.18])
AM_GNU_GETTEXT([external])
###############################################################################
# Checks for header files.
###############################################################################
@ -573,6 +574,9 @@ AC_CHECK_HEADERS([fcntl.h limits.h sys/time.h],
[],
[AC_MSG_ERROR([Required header file(s) are missing.])])
# This allows the use of the intrinsic functions if they are available.
AC_CHECK_HEADERS([immintrin.h])
###############################################################################
# Checks for typedefs, structures, and compiler characteristics.
@ -681,6 +685,15 @@ AM_CONDITIONAL([COND_INTERNAL_SHA256],
&& test "x$ac_cv_func_SHA256Init" != xyes \
&& test "x$ac_cv_func_CC_SHA256_Init" != xyes])
# Check for SSE2 intrinsics.
AC_CHECK_DECL([_mm_movemask_epi8],
[AC_DEFINE([HAVE__MM_MOVEMASK_EPI8], [1],
[Define to 1 if _mm_movemask_epi8 is available.])],
[],
[#ifdef HAVE_IMMINTRIN_H
#include <immintrin.h>
#endif])
###############################################################################
# If using GCC, set some additional AM_CFLAGS:

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@ -8,6 +8,7 @@
liblzma_la_SOURCES += \
common/common.c \
common/common.h \
common/memcmplen.h \
common/block_util.c \
common/easy_preset.c \
common/easy_preset.h \

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@ -0,0 +1,170 @@
///////////////////////////////////////////////////////////////////////////////
//
/// \file memcmplen.h
/// \brief Optimized comparison of two buffers
//
// Author: Lasse Collin
//
// This file has been put into the public domain.
// You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////
#ifndef LZMA_MEMCMPLEN_H
#define LZMA_MEMCMPLEN_H
#include "common.h"
#ifdef HAVE_IMMINTRIN_H
# include <immintrin.h>
#endif
/// How many extra bytes lzma_memcmplen() may read. This depends on
/// the method but since it is just a few bytes the biggest possible
/// value is used here.
#define LZMA_MEMCMPLEN_EXTRA 16
/// Find out how many equal bytes the two buffers have.
///
/// \param buf1 First buffer
/// \param buf2 Second buffer
/// \param len How many bytes have already been compared and will
/// be assumed to match
/// \param limit How many bytes to compare at most, including the
/// already-compared bytes. This must be significantly
/// smaller than UINT32_MAX to avoid integer overflows.
/// Up to LZMA_MEMCMPLEN_EXTRA bytes may be read past
/// the specified limit from both buf1 and buf2.
///
/// \return Number of equal bytes in the buffers is returned.
/// This is always at least len and at most limit.
static inline uint32_t lzma_attribute((__always_inline__))
lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2,
uint32_t len, uint32_t limit)
{
assert(len <= limit);
assert(limit <= UINT32_MAX / 2);
#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
&& ((TUKLIB_GNUC_REQ(3, 4) && defined(__x86_64__)) \
|| (defined(__INTEL_COMPILER) && defined(__x86_64__)) \
|| (defined(__INTEL_COMPILER) && defined(_M_X64)) \
|| (defined(_MSC_VER) && defined(_M_X64)))
// NOTE: This will use 64-bit unaligned access which
// TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit, but
// it's convenient here at least as long as it's x86-64 only.
//
// I keep this x86-64 only for now since that's where I know this
// to be a good method. This may be fine on other 64-bit CPUs too.
// On big endian one should use xor instead of subtraction and switch
// to __builtin_clzll().
while (len < limit) {
const uint64_t x = *(const uint64_t *)(buf1 + len)
- *(const uint64_t *)(buf2 + len);
if (x != 0) {
# if defined(_M_X64) // MSVC or Intel C compiler on Windows
unsigned long tmp;
_BitScanForward64(&tmp, x);
len += (uint32_t)tmp >> 3;
# else // GCC, clang, or Intel C compiler
len += (uint32_t)__builtin_ctzll(x) >> 3;
# endif
return my_min(len, limit);
}
len += 8;
}
return limit;
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
&& defined(HAVE__MM_MOVEMASK_EPI8) \
&& ((defined(__GNUC__) && defined(__SSE2_MATH__)) \
|| (defined(__INTEL_COMPILER) && defined(__SSE2__)) \
|| (defined(_MSC_VER) && defined(_M_IX86_FP) \
&& _M_IX86_FP >= 2))
// NOTE: Like above, this will use 128-bit unaligned access which
// TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit.
//
// SSE2 version for 32-bit and 64-bit x86. On x86-64 the above
// version is sometimes significantly faster and sometimes
// slightly slower than this SSE2 version, so this SSE2
// version isn't used on x86-64.
while (len < limit) {
const uint32_t x = 0xFFFF ^ _mm_movemask_epi8(_mm_cmpeq_epi8(
_mm_loadu_si128((const __m128i *)(buf1 + len)),
_mm_loadu_si128((const __m128i *)(buf2 + len))));
if (x != 0) {
# if defined(__INTEL_COMPILER)
len += _bit_scan_forward(x);
# elif defined(_MSC_VER)
unsigned long tmp;
_BitScanForward(&tmp, x);
len += tmp;
# else
len += __builtin_ctz(x);
# endif
return my_min(len, limit);
}
len += 16;
}
return limit;
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && !defined(WORDS_BIGENDIAN)
// Generic 32-bit little endian method
while (len < limit) {
uint32_t x = *(const uint32_t *)(buf1 + len)
- *(const uint32_t *)(buf2 + len);
if (x != 0) {
if ((x & 0xFFFF) == 0) {
len += 2;
x >>= 16;
}
if ((x & 0xFF) == 0)
++len;
return my_min(len, limit);
}
len += 4;
}
return limit;
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && defined(WORDS_BIGENDIAN)
// Generic 32-bit big endian method
while (len < limit) {
uint32_t x = *(const uint32_t *)(buf1 + len)
^ *(const uint32_t *)(buf2 + len);
if (x != 0) {
if ((x & 0xFFFF0000) == 0) {
len += 2;
x <<= 16;
}
if ((x & 0xFF000000) == 0)
++len;
return my_min(len, limit);
}
len += 4;
}
return limit;
#else
// Simple portable version that doesn't use unaligned access.
while (len < limit && buf1[len] == buf2[len])
++len;
return len;
#endif
}
#endif