1/*
2 * Copyright (C) 2010, Robert Eisele <robert@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
36static 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
50unsigned 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 = 0xffffffffU;
60 for (size_t i = 0; i < buffer.size(); ++i)
61 crc = crcTable[(crc ^ buffer[i]) & 0xff] ^ ((crc >> 8) & 0x00ffffffU);
62 return crc ^ 0xffffffffU;
63}
64
65