archive_crc32.h revision 358090 
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: stable/10/contrib/libarchive/libarchive/archive_crc32.h 358090 2020-02-19 01:51:44Z mm $
26 */
27
28#ifndef ARCHIVE_CRC32_H
29#define ARCHIVE_CRC32_H
30
31#ifndef __LIBARCHIVE_BUILD
32#error This header is only to be used internally to libarchive.
33#endif
34
35/*
36 * When zlib is unavailable, we should still be able to validate
37 * uncompressed zip archives.  That requires us to be able to compute
38 * the CRC32 check value.  This is a drop-in compatible replacement
39 * for crc32() from zlib.  It's slower than the zlib implementation,
40 * but still pretty fast: This runs about 300MB/s on my 3GHz P4
41 * compared to about 800MB/s for the zlib implementation.
42 */
43static unsigned long
44crc32(unsigned long crc, const void *_p, size_t len)
45{
46	unsigned long crc2, b, i;
47	const unsigned char *p = _p;
48	static volatile int crc_tbl_inited = 0;
49	static unsigned long crc_tbl[256];
50
51	if (!crc_tbl_inited) {
52		for (b = 0; b < 256; ++b) {
53			crc2 = b;
54			for (i = 8; i > 0; --i) {
55				if (crc2 & 1)
56					crc2 = (crc2 >> 1) ^ 0xedb88320UL;
57				else
58					crc2 = (crc2 >> 1);
59			}
60			crc_tbl[b] = crc2;
61		}
62		crc_tbl_inited = 1;
63	}
64
65	crc = crc ^ 0xffffffffUL;
66	/* A use of this loop is about 20% - 30% faster than
67	 * no use version in any optimization option of gcc.  */
68	for (;len >= 8; len -= 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		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
76		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
77	}
78	while (len--)
79		crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
80	return (crc ^ 0xffffffffUL);
81}
82
83#endif
84