1 /*
2 * CRC32 using the polynomial from IEEE-802.3
3 *
4 * Authors: Lasse Collin <lasse.collin@tukaani.org>
5 * Igor Pavlov <https://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
28 STATIC_RW_DATA uint32_t xz_crc32_table[256];
29
30 XZ_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
49 XZ_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
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