xref: /openbmc/linux/lib/xz/xz_crc32.c (revision 09b06c25)
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