diff options
Diffstat (limited to '')
| -rw-r--r-- | src/liblzma/check/crc32_fast.c | 158 |
1 files changed, 140 insertions, 18 deletions
diff --git a/src/liblzma/check/crc32_fast.c b/src/liblzma/check/crc32_fast.c index eed7350..16dbb74 100644 --- a/src/liblzma/check/crc32_fast.c +++ b/src/liblzma/check/crc32_fast.c @@ -1,35 +1,40 @@ +// SPDX-License-Identifier: 0BSD + /////////////////////////////////////////////////////////////////////////////// // /// \file crc32.c /// \brief CRC32 calculation -/// -/// Calculate the CRC32 using the slice-by-eight algorithm. -/// It is explained in this document: -/// http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf -/// The code in this file is not the same as in Intel's paper, but -/// the basic principle is identical. -// -// Author: Lasse Collin // -// This file has been put into the public domain. -// You can do whatever you want with this file. +// Authors: Lasse Collin +// Ilya Kurdyukov +// Hans Jansen // /////////////////////////////////////////////////////////////////////////////// #include "check.h" -#include "crc_macros.h" +#include "crc_common.h" + +#if defined(CRC_X86_CLMUL) +# define BUILDING_CRC32_CLMUL +# include "crc_x86_clmul.h" +#elif defined(CRC32_ARM64) +# include "crc32_arm64.h" +#endif -// If you make any changes, do some benchmarking! Seemingly unrelated -// changes can very easily ruin the performance (and very probably is -// very compiler dependent). -extern LZMA_API(uint32_t) -lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc) +#ifdef CRC32_GENERIC + +/////////////////// +// Generic CRC32 // +/////////////////// + +static uint32_t +crc32_generic(const uint8_t *buf, size_t size, uint32_t crc) { crc = ~crc; #ifdef WORDS_BIGENDIAN - crc = bswap32(crc); + crc = byteswap32(crc); #endif if (size > 8) { @@ -75,8 +80,125 @@ lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc) crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc); #ifdef WORDS_BIGENDIAN - crc = bswap32(crc); + crc = byteswap32(crc); #endif return ~crc; } +#endif + + +#if defined(CRC32_GENERIC) && defined(CRC32_ARCH_OPTIMIZED) + +////////////////////////// +// Function dispatching // +////////////////////////// + +// If both the generic and arch-optimized implementations are built, then +// the function to use is selected at runtime because the system running +// the binary might not have the arch-specific instruction set extension(s) +// available. The dispatch methods in order of priority: +// +// 1. Constructor. This method uses __attribute__((__constructor__)) to +// set crc32_func at load time. This avoids extra computation (and any +// unlikely threading bugs) on the first call to lzma_crc32() to decide +// which implementation should be used. +// +// 2. First Call Resolution. On the very first call to lzma_crc32(), the +// call will be directed to crc32_dispatch() instead. This will set the +// appropriate implementation function and will not be called again. +// This method does not use any kind of locking but is safe because if +// multiple threads run the dispatcher simultaneously then they will all +// set crc32_func to the same value. + +typedef uint32_t (*crc32_func_type)( + const uint8_t *buf, size_t size, uint32_t crc); + +// This resolver is shared between all dispatch methods. +static crc32_func_type +crc32_resolve(void) +{ + return is_arch_extension_supported() + ? &crc32_arch_optimized : &crc32_generic; +} + + +#ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR +// Constructor method. +# define CRC32_SET_FUNC_ATTR __attribute__((__constructor__)) +static crc32_func_type crc32_func; +#else +// First Call Resolution method. +# define CRC32_SET_FUNC_ATTR +static uint32_t crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc); +static crc32_func_type crc32_func = &crc32_dispatch; +#endif + +CRC32_SET_FUNC_ATTR +static void +crc32_set_func(void) +{ + crc32_func = crc32_resolve(); + return; +} + +#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR +static uint32_t +crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc) +{ + // When __attribute__((__constructor__)) isn't supported, set the + // function pointer without any locking. If multiple threads run + // the detection code in parallel, they will all end up setting + // the pointer to the same value. This avoids the use of + // mythread_once() on every call to lzma_crc32() but this likely + // isn't strictly standards compliant. Let's change it if it breaks. + crc32_set_func(); + return crc32_func(buf, size, crc); +} + +#endif +#endif + + +extern LZMA_API(uint32_t) +lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc) +{ +#if defined(CRC32_GENERIC) && defined(CRC32_ARCH_OPTIMIZED) + // On x86-64, if CLMUL is available, it is the best for non-tiny + // inputs, being over twice as fast as the generic slice-by-four + // version. However, for size <= 16 it's different. In the extreme + // case of size == 1 the generic version can be five times faster. + // At size >= 8 the CLMUL starts to become reasonable. It + // varies depending on the alignment of buf too. + // + // The above doesn't include the overhead of mythread_once(). + // At least on x86-64 GNU/Linux, pthread_once() is very fast but + // it still makes lzma_crc32(buf, 1, crc) 50-100 % slower. When + // size reaches 12-16 bytes the overhead becomes negligible. + // + // So using the generic version for size <= 16 may give better + // performance with tiny inputs but if such inputs happen rarely + // it's not so obvious because then the lookup table of the + // generic version may not be in the processor cache. +#ifdef CRC_USE_GENERIC_FOR_SMALL_INPUTS + if (size <= 16) + return crc32_generic(buf, size, crc); +#endif + +/* +#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR + // See crc32_dispatch(). This would be the alternative which uses + // locking and doesn't use crc32_dispatch(). Note that on Windows + // this method needs Vista threads. + mythread_once(crc64_set_func); +#endif +*/ + return crc32_func(buf, size, crc); + +#elif defined(CRC32_ARCH_OPTIMIZED) + return crc32_arch_optimized(buf, size, crc); + +#else + return crc32_generic(buf, size, crc); +#endif +} |