70 lines
2.5 KiB
C++
70 lines
2.5 KiB
C++
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/*
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* libjingle
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* Copyright 2012, Google, Inc.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
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* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "talk/base/crc32.h"
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#include "talk/base/basicdefs.h"
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namespace talk_base {
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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 kCrc32Polynomial = 0xEDB88320;
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static uint32 kCrc32Table[256] = { 0 };
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static void EnsureCrc32TableInited() {
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if (kCrc32Table[ARRAY_SIZE(kCrc32Table) - 1])
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return; // already inited
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for (uint32 i = 0; i < ARRAY_SIZE(kCrc32Table); ++i) {
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uint32 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 UpdateCrc32(uint32 start, const void* buf, size_t len) {
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EnsureCrc32TableInited();
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uint32 c = start ^ 0xFFFFFFFF;
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const uint8* u = static_cast<const uint8*>(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 talk_base
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