1 ///////////////////////////////////////////////////////////////////////////////
4 /// \brief CRC32 calculation
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.
12 // Author: Lasse Collin
14 // This file has been put into the public domain.
15 // You can do whatever you want with this file.
17 ///////////////////////////////////////////////////////////////////////////////
20 #include "crc_macros.h"
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)
31 #ifdef WORDS_BIGENDIAN
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);
43 // Calculate the position where to stop.
44 const uint8_t *const limit = buf + (size & ~(size_t)(7));
46 // Calculate how many bytes must be calculated separately
47 // before returning the result.
50 // Calculate the CRC32 using the slice-by-eight algorithm.
52 crc ^= *(const uint32_t *)(buf);
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)];
60 const uint32_t tmp = *(const uint32_t *)(buf);
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)]
69 ^ lzma_crc32_table[1][C(tmp)]
70 ^ lzma_crc32_table[0][D(tmp)];
75 crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
77 #ifdef WORDS_BIGENDIAN