/////////////////////////////////////////////////////////////////////////////// // /// \file crc32.c /// \brief CRC32 calculation // // This code has been put into the public domain. // // This library is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. // /////////////////////////////////////////////////////////////////////////////// #include "check.h" #include "crc_macros.h" // If you make any changes, do some bench marking! 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 = bswap_32(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. // It is explained in this document: // http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf // // The code below is different than the code in Intel's // paper, but the principle is identical. This should be // faster with GCC than Intel's code. This is tested only // with GCC 3.4.6 and 4.1.2 on x86, so your results may vary. // // Using -Os and -fomit-frame-pointer seem to give the best // results at least with GCC 4.1.2 on x86. It's sill far // from the speed of hand-optimized assembler. while (buf < limit) { crc ^= *(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 = *(uint32_t *)(buf); buf += 4; // 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 = bswap_32(crc); #endif return ~crc; }