diff options
Diffstat (limited to 'src/liblzma/check/crc32_fast.c')
| -rw-r--r-- | src/liblzma/check/crc32_fast.c | 30 |
1 files changed, 12 insertions, 18 deletions
diff --git a/src/liblzma/check/crc32_fast.c b/src/liblzma/check/crc32_fast.c index 61eacd61..a308eff5 100644 --- a/src/liblzma/check/crc32_fast.c +++ b/src/liblzma/check/crc32_fast.c @@ -2,12 +2,17 @@ // /// \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. // -// This code has been put into the public domain. +// Author: Lasse Collin // -// 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. +// This file has been put into the public domain. +// You can do whatever you want with this file. // /////////////////////////////////////////////////////////////////////////////// @@ -43,17 +48,6 @@ lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc) 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; @@ -66,9 +60,9 @@ lzma_crc32(const uint8_t *buf, size_t size, uint32_t 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. + // 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 |