1 /* 2 * Copyright (C) 2010, Robert Eisele <robert (at) xarg.org> All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are 6 * met: 7 * 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above 11 * copyright notice, this list of conditions and the following disclaimer 12 * in the documentation and/or other materials provided with the 13 * distribution. 14 * * Neither the name of Google Inc. nor the names of its 15 * contributors may be used to endorse or promote products derived from 16 * this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31 #include "config.h" 32 #include "CyclicRedundancyCheck.h" 33 34 #include <wtf/Vector.h> 35 36 static void makeCrcTable(unsigned crcTable[256]) 37 { 38 for (unsigned i = 0; i < 256; i++) { 39 unsigned c = i; 40 for (int k = 0; k < 8; k++) { 41 if (c & 1) 42 c = -306674912 ^ ((c >> 1) & 0x7fffffff); 43 else 44 c = c >> 1; 45 } 46 crcTable[i] = c; 47 } 48 } 49 50 unsigned computeCrc(const Vector<unsigned char>& buffer) 51 { 52 static unsigned crcTable[256]; 53 static bool crcTableComputed = false; 54 if (!crcTableComputed) { 55 makeCrcTable(crcTable); 56 crcTableComputed = true; 57 } 58 59 unsigned crc = 0xffffffffL; 60 for (size_t i = 0; i < buffer.size(); ++i) 61 crc = crcTable[(crc ^ buffer[i]) & 0xff] ^ ((crc >> 8) & 0x00ffffffL); 62 return crc ^ 0xffffffffL; 63 } 64 65
