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 "private.h"
19 
20 XZ_EXTERN uint32_t INITDATA xz_crc32_table[256];
21 
xz_crc32_init(void)22 XZ_EXTERN void INIT xz_crc32_init(void)
23 {
24 	const uint32_t poly = 0xEDB88320;
25 
26 	uint32_t i;
27 	uint32_t j;
28 	uint32_t r;
29 
30 	for (i = 0; i < 256; ++i) {
31 		r = i;
32 		for (j = 0; j < 8; ++j)
33 			r = (r >> 1) ^ (poly & ~((r & 1) - 1));
34 
35 		xz_crc32_table[i] = r;
36 	}
37 
38 	return;
39 }
40 
xz_crc32(const uint8_t * buf,size_t size,uint32_t crc)41 XZ_EXTERN uint32_t INIT xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
42 {
43 	crc = ~crc;
44 
45 	while (size != 0) {
46 		crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
47 		--size;
48 	}
49 
50 	return ~crc;
51 }
52