xz_crc32.c revision 0578287ba49f36d031f6d61bb53f5b54f56c65a3 
1/*
2 * CRC32 using the polynomial from IEEE-802.3
3 *
4 * Authors: Lasse Collin <lasse.collin@tukaani.org>
5 *          Igor Pavlov <http://7-zip.org/>
6 *
7 * This file has been put into the public domain.
8 * You can do whatever you want with this file.
9 */
10
11/*
12 * This is not the fastest implementation, but it is pretty compact.
13 * The fastest versions of xz_crc32() on modern CPUs without hardware
14 * accelerated CRC instruction are 3-5 times as fast as this version,
15 * but they are bigger and use more memory for the lookup table.
16 */
17
18#include "xz_private.h"
19
20/*
21 * STATIC_RW_DATA is used in the pre-boot environment on some architectures.
22 * See <linux/decompress/mm.h> for details.
23 */
24#ifndef STATIC_RW_DATA
25#	define STATIC_RW_DATA static
26#endif
27
28STATIC_RW_DATA uint32_t xz_crc32_table[256];
29
30XZ_EXTERN void xz_crc32_init(void)
31{
32	const uint32_t poly = 0xEDB88320;
33
34	uint32_t i;
35	uint32_t j;
36	uint32_t r;
37
38	for (i = 0; i < 256; ++i) {
39		r = i;
40		for (j = 0; j < 8; ++j)
41			r = (r >> 1) ^ (poly & ~((r & 1) - 1));
42
43		xz_crc32_table[i] = r;
44	}
45
46	return;
47}
48
49XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
50{
51	crc = ~crc;
52
53	while (size != 0) {
54		crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
55		--size;
56	}
57
58	return ~crc;
59}
60