projects / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 24fa0402 LC |
1 | /* |
| 2 | * CRC32 using the polynomial from IEEE-802.3 | |
| 3 | * | |
| 4 | * Authors: Lasse Collin <[email protected]> | |
| 5 | * Igor Pavlov <http://7-zip.org/> | |
| 6 | * | |
| 7 | * This file has been put into the public domain. | |
| 8 | * You can do whatever you want with this file. | |
| 9 | */ | |
| 10 | ||
| 11 | /* | |
| 12 | * This is not the fastest implementation, but it is pretty compact. | |
| 13 | * The fastest versions of xz_crc32() on modern CPUs without hardware | |
| 14 | * accelerated CRC instruction are 3-5 times as fast as this version, | |
| 15 | * but they are bigger and use more memory for the lookup table. | |
| 16 | */ | |
| 17 | ||
| 18 | #include "xz_private.h" | |
| 19 | ||
| 20 | /* | |
| 21 | * STATIC_RW_DATA is used in the pre-boot environment on some architectures. | |
| 22 | * See <linux/decompress/mm.h> for details. | |
| 23 | */ | |
| 24 | #ifndef STATIC_RW_DATA | |
| 25 | # define STATIC_RW_DATA static | |
| 26 | #endif | |
| 27 | ||
| 28 | STATIC_RW_DATA uint32_t xz_crc32_table[256]; | |
| 29 | ||
| 30 | XZ_EXTERN void xz_crc32_init(void) | |
| 31 | { | |
| 32 | const uint32_t poly = 0xEDB88320; | |
| 33 | ||
| 34 | uint32_t i; | |
| 35 | uint32_t j; | |
| 36 | uint32_t r; | |
| 37 | ||
| 38 | for (i = 0; i < 256; ++i) { | |
| 39 | r = i; | |
| 40 | for (j = 0; j < 8; ++j) | |
| 41 | r = (r >> 1) ^ (poly & ~((r & 1) - 1)); | |
| 42 | ||
| 43 | xz_crc32_table[i] = r; | |
| 44 | } | |
| 45 | ||
| 46 | return; | |
| 47 | } | |
| 48 | ||
| 49 | XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc) | |
| 50 | { | |
| 51 | crc = ~crc; | |
| 52 | ||
| 53 | while (size != 0) { | |
| 54 | crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8); | |
| 55 | --size; | |
| 56 | } | |
| 57 | ||
| 58 | return ~crc; | |
| 59 | } |