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 * $FreeBSD$ 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 */ 40 static unsigned long 41 crc32(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