1 /* vi: set sw=4 ts=4: */
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
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.
13 * endian = 1: big-endian
14 * endian = 0: little-endian
16 * Licensed under GPLv2, see file LICENSE in this source tree.
21 uint32_t *global_crc32_table;
23 uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian)
25 uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
30 crc_table = xmalloc(256 * sizeof(uint32_t));
32 for (i = 0; i < 256; i++) {
33 c = endian ? (i << 24) : i;
36 c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
38 c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
43 return crc_table - 256;
46 uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
48 const void *end = (uint8_t*)buf + len;
51 val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf];
52 buf = (uint8_t*)buf + 1;
57 uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
59 const void *end = (uint8_t*)buf + len;
62 val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8);
63 buf = (uint8_t*)buf + 1;