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/*-
* Copyright (c) 2009 Joerg Sonnenberger
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* $FreeBSD: head/lib/libarchive/archive_crc32.h 201102 2009-12-28 03:11:36Z kientzle $
*/

#ifndef __LIBARCHIVE_BUILD
#error This header is only to be used internally to libarchive.
#endif

/*
* When zlib is unavailable, we should still be able to validate
* uncompressed zip archives. That requires us to be able to compute
* the CRC32 check value. This is a drop-in compatible replacement
* for crc32() from zlib. It's slower than the zlib implementation,
* but still pretty fast: This runs about 300MB/s on my 3GHz P4
* compared to about 800MB/s for the zlib implementation.
*/
static unsigned long
crc32(unsigned long crc, const void *_p, size_t len)
{
unsigned long crc2, b, i;
const unsigned char *p = _p;
static volatile int crc_tbl_inited = 0;
static unsigned long crc_tbl[256];

if (!crc_tbl_inited) {
for (b = 0; b < 256; ++b) {
crc2 = b;
for (i = 8; i > 0; --i) {
if (crc2 & 1)
crc2 = (crc2 >> 1) ^ 0xedb88320UL;
else
crc2 = (crc2 >> 1);
}
crc_tbl[b] = crc2;
}
crc_tbl_inited = 1;
}

crc = crc ^ 0xffffffffUL;
/* A use of this loop is about 20% - 30% faster than
* no use version in any optimization option of gcc. */
for (;len >= 8; len -= 8) {
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
}
while (len--)
crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
return (crc ^ 0xffffffffUL);
}
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