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