1 /* vi: set sw=4 ts=4: */
2 /*
3 * CRC32 table fill function
4 * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
5 * (I can't really claim much credit however, as the algorithm is
6 * very well-known)
7 *
8 * The following function creates a CRC32 table depending on whether
9 * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
10 * required. Admittedly, there are other CRC32 polynomials floating
11 * around, but Busybox doesn't use them.
12 *
13 * endian = 1: big-endian
14 * endian = 0: little-endian
15 *
16 * Licensed under GPLv2, see file LICENSE in this source tree.
17 */
18 #include "libbb.h"
19
20 uint32_t *global_crc32_table;
21
crc32_filltable(uint32_t * crc_table,int endian)22 uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian)
23 {
24 uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
25 uint32_t c;
26 unsigned i, j;
27
28 if (!crc_table)
29 crc_table = xmalloc(256 * sizeof(uint32_t));
30
31 for (i = 0; i < 256; i++) {
32 c = endian ? (i << 24) : i;
33 for (j = 8; j; j--) {
34 if (endian)
35 c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
36 else
37 c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
38 }
39 *crc_table++ = c;
40 }
41
42 return crc_table - 256;
43 }
44 /* Common uses: */
crc32_new_table_le(void)45 uint32_t* FAST_FUNC crc32_new_table_le(void)
46 {
47 return crc32_filltable(NULL, 0);
48 }
global_crc32_new_table_le(void)49 uint32_t* FAST_FUNC global_crc32_new_table_le(void)
50 {
51 global_crc32_table = crc32_new_table_le();
52 return global_crc32_table;
53 }
54
crc32_block_endian1(uint32_t val,const void * buf,unsigned len,uint32_t * crc_table)55 uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
56 {
57 const void *end = (uint8_t*)buf + len;
58
59 while (buf != end) {
60 val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf];
61 buf = (uint8_t*)buf + 1;
62 }
63 return val;
64 }
65
crc32_block_endian0(uint32_t val,const void * buf,unsigned len,uint32_t * crc_table)66 uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
67 {
68 const void *end = (uint8_t*)buf + len;
69
70 while (buf != end) {
71 val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8);
72 buf = (uint8_t*)buf + 1;
73 }
74 return val;
75 }
76