1 /////////////////////////////////////////////////////////////////////////////// 2 // 3 /// \file crc32.c 4 /// \brief CRC32 calculation 5 /// 6 /// Calculate the CRC32 using the slice-by-eight algorithm. 7 /// It is explained in this document: 8 /// http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf 9 /// The code in this file is not the same as in Intel's paper, but 10 /// the basic principle is identical. 11 // 12 // Author: Lasse Collin 13 // 14 // This file has been put into the public domain. 15 // You can do whatever you want with this file. 16 // 17 /////////////////////////////////////////////////////////////////////////////// 18 19 #include "check.h" 20 #include "crc_macros.h" 21 22 23 // If you make any changes, do some benchmarking! Seemingly unrelated 24 // changes can very easily ruin the performance (and very probably is 25 // very compiler dependent). 26 extern LZMA_API(uint32_t) 27 lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc) 28 { 29 crc = ~crc; 30 31 #ifdef WORDS_BIGENDIAN 32 crc = bswap32(crc); 33 #endif 34 35 if (size > 8) { 36 // Fix the alignment, if needed. The if statement above 37 // ensures that this won't read past the end of buf[]. 38 while ((uintptr_t)(buf) & 7) { 39 crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc); 40 --size; 41 } 42 43 // Calculate the position where to stop. 44 const uint8_t *const limit = buf + (size & ~(size_t)(7)); 45 46 // Calculate how many bytes must be calculated separately 47 // before returning the result. 48 size &= (size_t)(7); 49 50 // Calculate the CRC32 using the slice-by-eight algorithm. 51 while (buf < limit) { 52 crc ^= *(const uint32_t *)(buf); 53 buf += 4; 54 55 crc = lzma_crc32_table[7][A(crc)] 56 ^ lzma_crc32_table[6][B(crc)] 57 ^ lzma_crc32_table[5][C(crc)] 58 ^ lzma_crc32_table[4][D(crc)]; 59 60 const uint32_t tmp = *(const uint32_t *)(buf); 61 buf += 4; 62 63 // At least with some compilers, it is critical for 64 // performance, that the crc variable is XORed 65 // between the two table-lookup pairs. 66 crc = lzma_crc32_table[3][A(tmp)] 67 ^ lzma_crc32_table[2][B(tmp)] 68 ^ crc 69 ^ lzma_crc32_table[1][C(tmp)] 70 ^ lzma_crc32_table[0][D(tmp)]; 71 } 72 } 73 74 while (size-- != 0) 75 crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc); 76 77 #ifdef WORDS_BIGENDIAN 78 crc = bswap32(crc); 79 #endif 80 81 return ~crc; 82 } 83