| /* |
| * libjingle |
| * Copyright 2012, Google, Inc. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are met: |
| * |
| * 1. Redistributions of source code must retain the above copyright notice, |
| * this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright notice, |
| * this list of conditions and the following disclaimer in the documentation |
| * and/or other materials provided with the distribution. |
| * 3. The name of the author may not be used to endorse or promote products |
| * derived from this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED |
| * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF |
| * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO |
| * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; |
| * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, |
| * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR |
| * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF |
| * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| #include "talk/base/crc32.h" |
| |
| #include "talk/base/basicdefs.h" |
| |
| namespace talk_base { |
| |
| // 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 kCrc32Polynomial = 0xEDB88320; |
| static uint32 kCrc32Table[256] = { 0 }; |
| |
| static void EnsureCrc32TableInited() { |
| if (kCrc32Table[ARRAY_SIZE(kCrc32Table) - 1]) |
| return; // already inited |
| for (uint32 i = 0; i < ARRAY_SIZE(kCrc32Table); ++i) { |
| uint32 c = i; |
| for (size_t j = 0; j < 8; ++j) { |
| if (c & 1) { |
| c = kCrc32Polynomial ^ (c >> 1); |
| } else { |
| c >>= 1; |
| } |
| } |
| kCrc32Table[i] = c; |
| } |
| } |
| |
| uint32 UpdateCrc32(uint32 start, const void* buf, size_t len) { |
| EnsureCrc32TableInited(); |
| |
| uint32 c = start ^ 0xFFFFFFFF; |
| const uint8* u = static_cast<const uint8*>(buf); |
| for (size_t i = 0; i < len; ++i) { |
| c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8); |
| } |
| return c ^ 0xFFFFFFFF; |
| } |
| |
| } // namespace talk_base |
| |