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///////////////////////////////////////////////////////////////////////////////
//
/// \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.
//
///////////////////////////////////////////////////////////////////////////////
#include "check.h"
#include "crc_macros.h"
// 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)
{
crc = ~crc;
#ifdef WORDS_BIGENDIAN
crc = bswap32(crc);
#endif
if (size > 8) {
// Fix the alignment, if needed. The if statement above
// ensures that this won't read past the end of buf[].
while ((uintptr_t)(buf) & 7) {
crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
--size;
}
// Calculate the position where to stop.
const uint8_t *const limit = buf + (size & ~(size_t)(7));
// Calculate how many bytes must be calculated separately
// before returning the result.
size &= (size_t)(7);
// Calculate the CRC32 using the slice-by-eight algorithm.
while (buf < limit) {
crc ^= *(const uint32_t *)(buf);
buf += 4;
crc = lzma_crc32_table[7][A(crc)]
^ lzma_crc32_table[6][B(crc)]
^ lzma_crc32_table[5][C(crc)]
^ lzma_crc32_table[4][D(crc)];
const uint32_t tmp = *(const uint32_t *)(buf);
buf += 4;
// At least with some compilers, it is critical for
// performance, that the crc variable is XORed
// between the two table-lookup pairs.
crc = lzma_crc32_table[3][A(tmp)]
^ lzma_crc32_table[2][B(tmp)]
^ crc
^ lzma_crc32_table[1][C(tmp)]
^ lzma_crc32_table[0][D(tmp)];
}
}
while (size-- != 0)
crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
#ifdef WORDS_BIGENDIAN
crc = bswap32(crc);
#endif
return ~crc;
}
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