blob: ac9836cc9e61b185e08687e75c73c380fc751762
1 | /* vi: set sw=4 ts=4: */ |
2 | /* |
3 | * CRC32 table fill function |
4 | * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com> |
5 | * (I can't really claim much credit however, as the algorithm is |
6 | * very well-known) |
7 | * |
8 | * The following function creates a CRC32 table depending on whether |
9 | * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is |
10 | * required. Admittedly, there are other CRC32 polynomials floating |
11 | * around, but Busybox doesn't use them. |
12 | * |
13 | * endian = 1: big-endian |
14 | * endian = 0: little-endian |
15 | * |
16 | * Licensed under GPLv2, see file LICENSE in this source tree. |
17 | */ |
18 | |
19 | #include "libbb.h" |
20 | |
21 | uint32_t *global_crc32_table; |
22 | |
23 | uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian) |
24 | { |
25 | uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; |
26 | uint32_t c; |
27 | int i, j; |
28 | |
29 | if (!crc_table) |
30 | crc_table = xmalloc(256 * sizeof(uint32_t)); |
31 | |
32 | for (i = 0; i < 256; i++) { |
33 | c = endian ? (i << 24) : i; |
34 | for (j = 8; j; j--) { |
35 | if (endian) |
36 | c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1); |
37 | else |
38 | c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1); |
39 | } |
40 | *crc_table++ = c; |
41 | } |
42 | |
43 | return crc_table - 256; |
44 | } |
45 | |
46 | uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table) |
47 | { |
48 | const void *end = (uint8_t*)buf + len; |
49 | |
50 | while (buf != end) { |
51 | val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf]; |
52 | buf = (uint8_t*)buf + 1; |
53 | } |
54 | return val; |
55 | } |
56 | |
57 | uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table) |
58 | { |
59 | const void *end = (uint8_t*)buf + len; |
60 | |
61 | while (buf != end) { |
62 | val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8); |
63 | buf = (uint8_t*)buf + 1; |
64 | } |
65 | return val; |
66 | } |
67 |