mirror of https://git.tukaani.org/xz.git
238 lines
7.3 KiB
C
238 lines
7.3 KiB
C
// SPDX-License-Identifier: 0BSD
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///////////////////////////////////////////////////////////////////////////////
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//
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/// \file crc32.c
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/// \brief CRC32 calculation
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//
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// Authors: Lasse Collin
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// Ilya Kurdyukov
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// Hans Jansen
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//
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///////////////////////////////////////////////////////////////////////////////
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#include "check.h"
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#include "crc_common.h"
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#if defined(CRC_X86_CLMUL)
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# define BUILDING_CRC32_CLMUL
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# include "crc_x86_clmul.h"
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#elif defined(CRC32_ARM64)
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# include "crc32_arm64.h"
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#endif
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#ifdef CRC32_GENERIC
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///////////////////
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// Generic CRC32 //
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///////////////////
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static uint32_t
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crc32_generic(const uint8_t *buf, size_t size, uint32_t crc)
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{
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crc = ~crc;
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#ifdef WORDS_BIGENDIAN
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crc = bswap32(crc);
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#endif
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if (size > 8) {
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// Fix the alignment, if needed. The if statement above
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// ensures that this won't read past the end of buf[].
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while ((uintptr_t)(buf) & 7) {
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crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
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--size;
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}
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// Calculate the position where to stop.
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const uint8_t *const limit = buf + (size & ~(size_t)(7));
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// Calculate how many bytes must be calculated separately
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// before returning the result.
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size &= (size_t)(7);
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// Calculate the CRC32 using the slice-by-eight algorithm.
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while (buf < limit) {
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crc ^= aligned_read32ne(buf);
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buf += 4;
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crc = lzma_crc32_table[7][A(crc)]
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^ lzma_crc32_table[6][B(crc)]
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^ lzma_crc32_table[5][C(crc)]
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^ lzma_crc32_table[4][D(crc)];
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const uint32_t tmp = aligned_read32ne(buf);
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buf += 4;
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// At least with some compilers, it is critical for
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// performance, that the crc variable is XORed
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// between the two table-lookup pairs.
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crc = lzma_crc32_table[3][A(tmp)]
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^ lzma_crc32_table[2][B(tmp)]
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^ crc
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^ lzma_crc32_table[1][C(tmp)]
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^ lzma_crc32_table[0][D(tmp)];
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}
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}
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while (size-- != 0)
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crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
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#ifdef WORDS_BIGENDIAN
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crc = bswap32(crc);
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#endif
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return ~crc;
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}
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#endif
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#if defined(CRC32_GENERIC) && defined(CRC32_ARCH_OPTIMIZED)
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//////////////////////////
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// Function dispatching //
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//////////////////////////
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// If both the generic and arch-optimized implementations are built, then
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// the function to use is selected at runtime because the system running
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// the binary might not have the arch-specific instruction set extension(s)
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// available. The three dispatch methods in order of priority:
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//
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// 1. Indirect function (ifunc). This method is slightly more efficient
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// than the constructor method because it will change the entry in the
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// Procedure Linkage Table (PLT) for the function either at load time or
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// at the first call. This avoids having to call the function through a
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// function pointer and will treat the function call like a regular call
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// through the PLT. ifuncs are created by using
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// __attribute__((__ifunc__("resolver"))) on a function which has no
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// body. The "resolver" is the name of the function that chooses at
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// runtime which implementation to use.
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//
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// 2. Constructor. This method uses __attribute__((__constructor__)) to
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// set crc32_func at load time. This avoids extra computation (and any
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// unlikely threading bugs) on the first call to lzma_crc32() to decide
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// which implementation should be used.
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//
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// 3. First Call Resolution. On the very first call to lzma_crc32(), the
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// call will be directed to crc32_dispatch() instead. This will set the
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// appropriate implementation function and will not be called again.
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// This method does not use any kind of locking but is safe because if
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// multiple threads run the dispatcher simultaneously then they will all
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// set crc32_func to the same value.
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typedef uint32_t (*crc32_func_type)(
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const uint8_t *buf, size_t size, uint32_t crc);
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// Clang 16.0.0 and older has a bug where it marks the ifunc resolver
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// function as unused since it is static and never used outside of
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// __attribute__((__ifunc__())).
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#if defined(CRC_USE_IFUNC) && defined(__clang__)
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# pragma GCC diagnostic push
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# pragma GCC diagnostic ignored "-Wunused-function"
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#endif
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// This resolver is shared between all three dispatch methods. It serves as
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// the ifunc resolver if ifunc is supported, otherwise it is called as a
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// regular function by the constructor or first call resolution methods.
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static crc32_func_type
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crc32_resolve(void)
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{
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return is_arch_extension_supported()
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? &crc32_arch_optimized : &crc32_generic;
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}
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#if defined(CRC_USE_IFUNC) && defined(__clang__)
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# pragma GCC diagnostic pop
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#endif
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#ifndef CRC_USE_IFUNC
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#ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
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// Constructor method.
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# define CRC32_SET_FUNC_ATTR __attribute__((__constructor__))
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static crc32_func_type crc32_func;
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#else
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// First Call Resolution method.
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# define CRC32_SET_FUNC_ATTR
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static uint32_t crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc);
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static crc32_func_type crc32_func = &crc32_dispatch;
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#endif
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CRC32_SET_FUNC_ATTR
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static void
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crc32_set_func(void)
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{
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crc32_func = crc32_resolve();
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return;
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}
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#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
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static uint32_t
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crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc)
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{
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// When __attribute__((__ifunc__(...))) and
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// __attribute__((__constructor__)) isn't supported, set the
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// function pointer without any locking. If multiple threads run
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// the detection code in parallel, they will all end up setting
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// the pointer to the same value. This avoids the use of
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// mythread_once() on every call to lzma_crc32() but this likely
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// isn't strictly standards compliant. Let's change it if it breaks.
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crc32_set_func();
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return crc32_func(buf, size, crc);
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}
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#endif
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#endif
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#endif
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#ifdef CRC_USE_IFUNC
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extern LZMA_API(uint32_t)
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lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
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__attribute__((__ifunc__("crc32_resolve")));
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#else
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extern LZMA_API(uint32_t)
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lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
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{
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#if defined(CRC32_GENERIC) && defined(CRC32_ARCH_OPTIMIZED)
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// On x86-64, if CLMUL is available, it is the best for non-tiny
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// inputs, being over twice as fast as the generic slice-by-four
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// version. However, for size <= 16 it's different. In the extreme
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// case of size == 1 the generic version can be five times faster.
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// At size >= 8 the CLMUL starts to become reasonable. It
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// varies depending on the alignment of buf too.
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//
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// The above doesn't include the overhead of mythread_once().
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// At least on x86-64 GNU/Linux, pthread_once() is very fast but
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// it still makes lzma_crc32(buf, 1, crc) 50-100 % slower. When
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// size reaches 12-16 bytes the overhead becomes negligible.
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//
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// So using the generic version for size <= 16 may give better
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// performance with tiny inputs but if such inputs happen rarely
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// it's not so obvious because then the lookup table of the
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// generic version may not be in the processor cache.
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#ifdef CRC_USE_GENERIC_FOR_SMALL_INPUTS
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if (size <= 16)
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return crc32_generic(buf, size, crc);
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#endif
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/*
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#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
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// See crc32_dispatch(). This would be the alternative which uses
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// locking and doesn't use crc32_dispatch(). Note that on Windows
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// this method needs Vista threads.
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mythread_once(crc64_set_func);
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#endif
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*/
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return crc32_func(buf, size, crc);
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#elif defined(CRC32_ARCH_OPTIMIZED)
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return crc32_arch_optimized(buf, size, crc);
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#else
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return crc32_generic(buf, size, crc);
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#endif
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}
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#endif
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