1 /*-
2 * Copyright (c) 2009 Joerg Sonnenberger
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26 #ifndef ARCHIVE_CRC32_H
27 #define ARCHIVE_CRC32_H
28
29 #ifndef __LIBARCHIVE_BUILD
30 #error This header is only to be used internally to libarchive.
31 #endif
32
33 /*
34 * When zlib is unavailable, we should still be able to validate
35 * uncompressed zip archives. That requires us to be able to compute
36 * the CRC32 check value. This is a drop-in compatible replacement
37 * for crc32() from zlib. It's slower than the zlib implementation,
38 * but still pretty fast: This runs about 300MB/s on my 3GHz P4
39 * compared to about 800MB/s for the zlib implementation.
40 */
41 static unsigned long
crc32(unsigned long crc,const void * _p,size_t len)42 crc32(unsigned long crc, const void *_p, size_t len)
43 {
44 unsigned long crc2, b, i;
45 const unsigned char *p = _p;
46 static volatile int crc_tbl_inited = 0;
47 static unsigned long crc_tbl[256];
48
49 if (!crc_tbl_inited) {
50 for (b = 0; b < 256; ++b) {
51 crc2 = b;
52 for (i = 8; i > 0; --i) {
53 if (crc2 & 1)
54 crc2 = (crc2 >> 1) ^ 0xedb88320UL;
55 else
56 crc2 = (crc2 >> 1);
57 }
58 crc_tbl[b] = crc2;
59 }
60 crc_tbl_inited = 1;
61 }
62
63 crc = crc ^ 0xffffffffUL;
64 /* A use of this loop is about 20% - 30% faster than
65 * no use version in any optimization option of gcc. */
66 for (;len >= 8; len -= 8) {
67 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
68 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
69 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
70 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
71 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
72 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
73 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
74 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
75 }
76 while (len--)
77 crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
78 return (crc ^ 0xffffffffUL);
79 }
80
81 #endif
82