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/*-
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* Copyright (c) 2009 Joerg Sonnenberger
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD: head/lib/libarchive/archive_crc32.h 201102 2009-12-28 03:11:36Z kientzle $
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*/
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#ifndef __LIBARCHIVE_BUILD
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#error This header is only to be used internally to libarchive.
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#endif
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/*
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* When zlib is unavailable, we should still be able to validate
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* uncompressed zip archives. That requires us to be able to compute
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* the CRC32 check value. This is a drop-in compatible replacement
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* for crc32() from zlib. It's slower than the zlib implementation,
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* but still pretty fast: This runs about 300MB/s on my 3GHz P4
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* compared to about 800MB/s for the zlib implementation.
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*/
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static unsigned long
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crc32(unsigned long crc, const void *_p, size_t len)
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{
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unsigned long crc2, b, i;
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const unsigned char *p = _p;
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static volatile int crc_tbl_inited = 0;
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static unsigned long crc_tbl[256];
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if (!crc_tbl_inited) {
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for (b = 0; b < 256; ++b) {
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crc2 = b;
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for (i = 8; i > 0; --i) {
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if (crc2 & 1)
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crc2 = (crc2 >> 1) ^ 0xedb88320UL;
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else
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crc2 = (crc2 >> 1);
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}
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crc_tbl[b] = crc2;
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}
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crc_tbl_inited = 1;
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}
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crc = crc ^ 0xffffffffUL;
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/* A use of this loop is about 20% - 30% faster than
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* no use version in any optimization option of gcc. */
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for (;len >= 8; len -= 8) {
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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}
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while (len--)
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crc = crc_tbl[(crc ^ *p++) & 0xff] ^ (crc >> 8);
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return (crc ^ 0xffffffffUL);
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}
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