1228753Smm/*-
2228753Smm * Copyright (c) 2009 Joerg  Sonnenberger
3228753Smm * All rights reserved.
4228753Smm *
5228753Smm * Redistribution and use in source and binary forms, with or without
6228753Smm * modification, are permitted provided that the following conditions
7228753Smm * are met:
8228753Smm * 1. Redistributions of source code must retain the above copyright
9228753Smm *    notice, this list of conditions and the following disclaimer.
10228753Smm * 2. Redistributions in binary form must reproduce the above copyright
11228753Smm *    notice, this list of conditions and the following disclaimer in the
12228753Smm *    documentation and/or other materials provided with the distribution.
13228753Smm *
14228753Smm * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
15228753Smm * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16228753Smm * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17228753Smm * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
18228753Smm * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19228753Smm * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20228753Smm * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21228753Smm * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22228753Smm * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23228753Smm * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24228753Smm *
25229592Smm * $FreeBSD$
26228753Smm */
27228753Smm
28228753Smm#ifndef __LIBARCHIVE_BUILD
29228753Smm#error This header is only to be used internally to libarchive.
30228753Smm#endif
31228753Smm
32228753Smm/*
33228753Smm * When zlib is unavailable, we should still be able to validate
34228753Smm * uncompressed zip archives.  That requires us to be able to compute
35228753Smm * the CRC32 check value.  This is a drop-in compatible replacement
36228753Smm * for crc32() from zlib.  It's slower than the zlib implementation,
37228753Smm * but still pretty fast: This runs about 300MB/s on my 3GHz P4
38228753Smm * compared to about 800MB/s for the zlib implementation.
39228753Smm */
40228753Smmstatic unsigned long
41228753Smmcrc32(unsigned long crc, const void *_p, size_t len)
42228753Smm{
43228753Smm	unsigned long crc2, b, i;
44228753Smm	const unsigned char *p = _p;
45228753Smm	static volatile int crc_tbl_inited = 0;
46228753Smm	static unsigned long crc_tbl[256];
47228753Smm
48228753Smm	if (!crc_tbl_inited) {
49228753Smm		for (b = 0; b < 256; ++b) {
50228753Smm			crc2 = b;
51228753Smm			for (i = 8; i > 0; --i) {
52228753Smm				if (crc2 & 1)
53228753Smm					crc2 = (crc2 >> 1) ^ 0xedb88320UL;
54228753Smm				else
55228753Smm					crc2 = (crc2 >> 1);
56228753Smm			}
57228753Smm			crc_tbl[b] = crc2;
58228753Smm		}
59228753Smm		crc_tbl_inited = 1;
60228753Smm	}
61228753Smm
62228753Smm	crc = crc ^ 0xffffffffUL;
63228753Smm	while (len--)
64228753Smm		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
65228753Smm	return (crc ^ 0xffffffffUL);
66228753Smm}
67