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* 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 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 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