source: branches/3.2/mindi-busybox/libbb/crc32.c @ 3232

Last change on this file since 3232 was 3232, checked in by bruno, 6 years ago
  • Update mindi-busybox to 1.21.1
File size: 1.7 KB
Line 
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
21uint32_t *global_crc32_table;
22
23uint32_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
46uint32_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
57uint32_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}
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