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/*
* Copyright 2012 The WebRTC Project Authors. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "webrtc/base/crc32.h"
#include "webrtc/base/arraysize.h"
namespace rtc {
// This implementation is based on the sample implementation in RFC 1952.
// CRC32 polynomial, in reversed form.
// See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check
static const uint32_t kCrc32Polynomial = 0xEDB88320;
static uint32_t kCrc32Table[256] = {0};
static void EnsureCrc32TableInited() {
if (kCrc32Table[arraysize(kCrc32Table) - 1])
return; // already inited
for (uint32_t i = 0; i < arraysize(kCrc32Table); ++i) {
uint32_t c = i;
for (size_t j = 0; j < 8; ++j) {
if (c & 1) {
c = kCrc32Polynomial ^ (c >> 1);
} else {
c >>= 1;
}
}
kCrc32Table[i] = c;
}
}
uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) {
EnsureCrc32TableInited();
uint32_t c = start ^ 0xFFFFFFFF;
const uint8_t* u = static_cast<const uint8_t*>(buf);
for (size_t i = 0; i < len; ++i) {
c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8);
}
return c ^ 0xFFFFFFFF;
}
} // namespace rtc
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