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