mirror of https://git.tukaani.org/xz.git
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
parent
765735cf52
commit
e1c8f1d01f
13
configure.ac
13
configure.ac
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@ -560,6 +560,7 @@ echo "Initializing gettext:"
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AM_GNU_GETTEXT_VERSION([0.18])
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AM_GNU_GETTEXT([external])
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###############################################################################
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# Checks for header files.
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###############################################################################
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@ -573,6 +574,9 @@ AC_CHECK_HEADERS([fcntl.h limits.h sys/time.h],
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[],
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[AC_MSG_ERROR([Required header file(s) are missing.])])
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# This allows the use of the intrinsic functions if they are available.
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AC_CHECK_HEADERS([immintrin.h])
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###############################################################################
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# Checks for typedefs, structures, and compiler characteristics.
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@ -681,6 +685,15 @@ AM_CONDITIONAL([COND_INTERNAL_SHA256],
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&& test "x$ac_cv_func_SHA256Init" != xyes \
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&& test "x$ac_cv_func_CC_SHA256_Init" != xyes])
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# Check for SSE2 intrinsics.
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AC_CHECK_DECL([_mm_movemask_epi8],
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[AC_DEFINE([HAVE__MM_MOVEMASK_EPI8], [1],
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[Define to 1 if _mm_movemask_epi8 is available.])],
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[],
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[#ifdef HAVE_IMMINTRIN_H
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#include <immintrin.h>
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#endif])
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###############################################################################
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# If using GCC, set some additional AM_CFLAGS:
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@ -8,6 +8,7 @@
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liblzma_la_SOURCES += \
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common/common.c \
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common/common.h \
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common/memcmplen.h \
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common/block_util.c \
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common/easy_preset.c \
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common/easy_preset.h \
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@ -0,0 +1,170 @@
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///////////////////////////////////////////////////////////////////////////////
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//
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/// \file memcmplen.h
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/// \brief Optimized comparison of two buffers
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//
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// Author: Lasse Collin
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//
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// This file has been put into the public domain.
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// You can do whatever you want with this file.
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//
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///////////////////////////////////////////////////////////////////////////////
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#ifndef LZMA_MEMCMPLEN_H
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#define LZMA_MEMCMPLEN_H
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#include "common.h"
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#ifdef HAVE_IMMINTRIN_H
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# include <immintrin.h>
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#endif
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/// How many extra bytes lzma_memcmplen() may read. This depends on
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/// the method but since it is just a few bytes the biggest possible
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/// value is used here.
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#define LZMA_MEMCMPLEN_EXTRA 16
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/// Find out how many equal bytes the two buffers have.
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///
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/// \param buf1 First buffer
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/// \param buf2 Second buffer
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/// \param len How many bytes have already been compared and will
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/// be assumed to match
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/// \param limit How many bytes to compare at most, including the
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/// already-compared bytes. This must be significantly
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/// smaller than UINT32_MAX to avoid integer overflows.
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/// Up to LZMA_MEMCMPLEN_EXTRA bytes may be read past
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/// the specified limit from both buf1 and buf2.
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///
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/// \return Number of equal bytes in the buffers is returned.
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/// This is always at least len and at most limit.
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static inline uint32_t lzma_attribute((__always_inline__))
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lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2,
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uint32_t len, uint32_t limit)
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{
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assert(len <= limit);
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assert(limit <= UINT32_MAX / 2);
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#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
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&& ((TUKLIB_GNUC_REQ(3, 4) && defined(__x86_64__)) \
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|| (defined(__INTEL_COMPILER) && defined(__x86_64__)) \
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|| (defined(__INTEL_COMPILER) && defined(_M_X64)) \
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|| (defined(_MSC_VER) && defined(_M_X64)))
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// NOTE: This will use 64-bit unaligned access which
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// TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit, but
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// it's convenient here at least as long as it's x86-64 only.
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//
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// I keep this x86-64 only for now since that's where I know this
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// to be a good method. This may be fine on other 64-bit CPUs too.
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// On big endian one should use xor instead of subtraction and switch
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// to __builtin_clzll().
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while (len < limit) {
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const uint64_t x = *(const uint64_t *)(buf1 + len)
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- *(const uint64_t *)(buf2 + len);
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if (x != 0) {
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# if defined(_M_X64) // MSVC or Intel C compiler on Windows
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unsigned long tmp;
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_BitScanForward64(&tmp, x);
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len += (uint32_t)tmp >> 3;
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# else // GCC, clang, or Intel C compiler
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len += (uint32_t)__builtin_ctzll(x) >> 3;
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# endif
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return my_min(len, limit);
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}
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len += 8;
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}
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return limit;
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#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
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&& defined(HAVE__MM_MOVEMASK_EPI8) \
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&& ((defined(__GNUC__) && defined(__SSE2_MATH__)) \
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|| (defined(__INTEL_COMPILER) && defined(__SSE2__)) \
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|| (defined(_MSC_VER) && defined(_M_IX86_FP) \
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&& _M_IX86_FP >= 2))
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// NOTE: Like above, this will use 128-bit unaligned access which
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// TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit.
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//
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// SSE2 version for 32-bit and 64-bit x86. On x86-64 the above
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// version is sometimes significantly faster and sometimes
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// slightly slower than this SSE2 version, so this SSE2
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// version isn't used on x86-64.
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while (len < limit) {
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const uint32_t x = 0xFFFF ^ _mm_movemask_epi8(_mm_cmpeq_epi8(
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_mm_loadu_si128((const __m128i *)(buf1 + len)),
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_mm_loadu_si128((const __m128i *)(buf2 + len))));
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if (x != 0) {
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# if defined(__INTEL_COMPILER)
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len += _bit_scan_forward(x);
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# elif defined(_MSC_VER)
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unsigned long tmp;
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_BitScanForward(&tmp, x);
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len += tmp;
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# else
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len += __builtin_ctz(x);
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# endif
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return my_min(len, limit);
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}
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len += 16;
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}
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return limit;
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#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && !defined(WORDS_BIGENDIAN)
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// Generic 32-bit little endian method
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while (len < limit) {
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uint32_t x = *(const uint32_t *)(buf1 + len)
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- *(const uint32_t *)(buf2 + len);
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if (x != 0) {
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if ((x & 0xFFFF) == 0) {
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len += 2;
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x >>= 16;
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}
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if ((x & 0xFF) == 0)
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++len;
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return my_min(len, limit);
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}
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len += 4;
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}
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return limit;
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#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && defined(WORDS_BIGENDIAN)
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// Generic 32-bit big endian method
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while (len < limit) {
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uint32_t x = *(const uint32_t *)(buf1 + len)
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^ *(const uint32_t *)(buf2 + len);
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if (x != 0) {
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if ((x & 0xFFFF0000) == 0) {
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len += 2;
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x <<= 16;
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}
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if ((x & 0xFF000000) == 0)
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++len;
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return my_min(len, limit);
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}
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len += 4;
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}
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return limit;
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#else
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// Simple portable version that doesn't use unaligned access.
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while (len < limit && buf1[len] == buf2[len])
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++len;
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return len;
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#endif
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}
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#endif
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