Contents of /tags/mkinitrd-6_5_1/busybox/libbb/crc32.c
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Wed Sep 7 17:51:16 2011 UTC (13 years ago) by niro
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Wed Sep 7 17:51:16 2011 UTC (13 years ago) by niro
File MIME type: text/plain
File size: 1110 byte(s)
tagged 'mkinitrd-6_5_1'
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 tarball for details. |
17 | */ |
18 | |
19 | #include "libbb.h" |
20 | |
21 | uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian) |
22 | { |
23 | uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; |
24 | uint32_t c; |
25 | int i, j; |
26 | |
27 | if (!crc_table) |
28 | crc_table = xmalloc(256 * sizeof(uint32_t)); |
29 | |
30 | for (i = 0; i < 256; i++) { |
31 | c = endian ? (i << 24) : i; |
32 | for (j = 8; j; j--) { |
33 | if (endian) |
34 | c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1); |
35 | else |
36 | c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1); |
37 | } |
38 | *crc_table++ = c; |
39 | } |
40 | |
41 | return crc_table - 256; |
42 | } |