xz_crc32.c

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