3 * Copyright 2012, Google, Inc.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
8 * 1. Redistributions of source code must retain the above copyright notice,
9 * this list of conditions and the following disclaimer.
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11 * this list of conditions and the following disclaimer in the documentation
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28 #include "talk/base/crc32.h"
30 #include "talk/base/basicdefs.h"
34 // This implementation is based on the sample implementation in RFC 1952.
36 // CRC32 polynomial, in reversed form.
37 // See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check
38 static const uint32 kCrc32Polynomial = 0xEDB88320;
39 static uint32 kCrc32Table[256] = { 0 };
41 static void EnsureCrc32TableInited() {
42 if (kCrc32Table[ARRAY_SIZE(kCrc32Table) - 1])
43 return; // already inited
44 for (uint32 i = 0; i < ARRAY_SIZE(kCrc32Table); ++i) {
46 for (size_t j = 0; j < 8; ++j) {
48 c = kCrc32Polynomial ^ (c >> 1);
57 uint32 UpdateCrc32(uint32 start, const void* buf, size_t len) {
58 EnsureCrc32TableInited();
60 uint32 c = start ^ 0xFFFFFFFF;
61 const uint8* u = static_cast<const uint8*>(buf);
62 for (size_t i = 0; i < len; ++i) {
63 c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8);
65 return c ^ 0xFFFFFFFF;
68 } // namespace talk_base