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1 | /* |
2 | * CRC32 using the polynomial from IEEE-802.3 | |
3 | * | |
4 | * Authors: Lasse Collin <lasse.collin@tukaani.org> | |
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 | ||
faa16bc4 | 18 | #include <linux/crc32poly.h> |
24fa0402 LC |
19 | #include "xz_private.h" |
20 | ||
21 | /* | |
22 | * STATIC_RW_DATA is used in the pre-boot environment on some architectures. | |
23 | * See <linux/decompress/mm.h> for details. | |
24 | */ | |
25 | #ifndef STATIC_RW_DATA | |
26 | # define STATIC_RW_DATA static | |
27 | #endif | |
28 | ||
29 | STATIC_RW_DATA uint32_t xz_crc32_table[256]; | |
30 | ||
31 | XZ_EXTERN void xz_crc32_init(void) | |
32 | { | |
faa16bc4 | 33 | const uint32_t poly = CRC32_POLY_LE; |
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34 | |
35 | uint32_t i; | |
36 | uint32_t j; | |
37 | uint32_t r; | |
38 | ||
39 | for (i = 0; i < 256; ++i) { | |
40 | r = i; | |
41 | for (j = 0; j < 8; ++j) | |
42 | r = (r >> 1) ^ (poly & ~((r & 1) - 1)); | |
43 | ||
44 | xz_crc32_table[i] = r; | |
45 | } | |
46 | ||
47 | return; | |
48 | } | |
49 | ||
50 | XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc) | |
51 | { | |
52 | crc = ~crc; | |
53 | ||
54 | while (size != 0) { | |
55 | crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8); | |
56 | --size; | |
57 | } | |
58 | ||
59 | return ~crc; | |
60 | } |