| henrike@webrtc.org | 0e118e7 | 2013-07-10 00:45:36 +0000 | [diff] [blame] | 1 | /* |
| 2 | * libjingle |
| 3 | * Copyright 2012, Google, Inc. |
| 4 | * |
| 5 | * Redistribution and use in source and binary forms, with or without |
| 6 | * modification, are permitted provided that the following conditions are met: |
| 7 | * |
| 8 | * 1. Redistributions of source code must retain the above copyright notice, |
| 9 | * this list of conditions and the following disclaimer. |
| 10 | * 2. Redistributions in binary form must reproduce the above copyright notice, |
| 11 | * this list of conditions and the following disclaimer in the documentation |
| 12 | * and/or other materials provided with the distribution. |
| 13 | * 3. The name of the author may not be used to endorse or promote products |
| 14 | * derived from this software without specific prior written permission. |
| 15 | * |
| 16 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED |
| 17 | * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF |
| 18 | * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO |
| 19 | * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 20 | * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| 21 | * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; |
| 22 | * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, |
| 23 | * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR |
| 24 | * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF |
| 25 | * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 26 | */ |
| 27 | |
| 28 | #include "talk/base/crc32.h" |
| 29 | |
| 30 | #include "talk/base/basicdefs.h" |
| 31 | |
| 32 | namespace talk_base { |
| 33 | |
| 34 | // This implementation is based on the sample implementation in RFC 1952. |
| 35 | |
| 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 }; |
| 40 | |
| 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) { |
| 45 | uint32 c = i; |
| 46 | for (size_t j = 0; j < 8; ++j) { |
| 47 | if (c & 1) { |
| 48 | c = kCrc32Polynomial ^ (c >> 1); |
| 49 | } else { |
| 50 | c >>= 1; |
| 51 | } |
| 52 | } |
| 53 | kCrc32Table[i] = c; |
| 54 | } |
| 55 | } |
| 56 | |
| 57 | uint32 UpdateCrc32(uint32 start, const void* buf, size_t len) { |
| 58 | EnsureCrc32TableInited(); |
| 59 | |
| 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); |
| 64 | } |
| 65 | return c ^ 0xFFFFFFFF; |
| 66 | } |
| 67 | |
| 68 | } // namespace talk_base |
| 69 | |