archive_crc32.h revision 232153 
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 * $FreeBSD: head/contrib/libarchive/libarchive/archive_crc32.h 232153 2012-02-25 10:58:02Z mm $
26 */
27
28#ifndef __LIBARCHIVE_BUILD
29#error This header is only to be used internally to libarchive.
30#endif
31
32/*
33 * When zlib is unavailable, we should still be able to validate
34 * uncompressed zip archives.  That requires us to be able to compute
35 * the CRC32 check value.  This is a drop-in compatible replacement
36 * for crc32() from zlib.  It's slower than the zlib implementation,
37 * but still pretty fast: This runs about 300MB/s on my 3GHz P4
38 * compared to about 800MB/s for the zlib implementation.
39 */
40static unsigned long
41crc32(unsigned long crc, const void *_p, size_t len)
42{
43	unsigned long crc2, b, i;
44	const unsigned char *p = _p;
45	static volatile int crc_tbl_inited = 0;
46	static unsigned long crc_tbl[256];
47
48	if (!crc_tbl_inited) {
49		for (b = 0; b < 256; ++b) {
50			crc2 = b;
51			for (i = 8; i > 0; --i) {
52				if (crc2 & 1)
53					crc2 = (crc2 >> 1) ^ 0xedb88320UL;
54				else
55					crc2 = (crc2 >> 1);
56			}
57			crc_tbl[b] = crc2;
58		}
59		crc_tbl_inited = 1;
60	}
61
62	crc = crc ^ 0xffffffffUL;
63	/* A use of this loop is about 20% - 30% faster than
64	 * no use version in any optimization option of gcc.  */
65	for (;len >= 8; len -= 8) {
66		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 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	}
75	while (len--)
76		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
77	return (crc ^ 0xffffffffUL);
78}
79