henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2012 The WebRTC Project Authors. All rights reserved. |
| 3 | * |
| 4 | * Use of this source code is governed by a BSD-style license |
| 5 | * that can be found in the LICENSE file in the root of the source |
| 6 | * tree. An additional intellectual property rights grant can be found |
| 7 | * in the file PATENTS. All contributing project authors may |
| 8 | * be found in the AUTHORS file in the root of the source tree. |
| 9 | */ |
| 10 | |
Mirko Bonadei | 92ea95e | 2017-09-15 04:47:31 | [diff] [blame] | 11 | #include "rtc_base/crc32.h" |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 12 | |
Mirko Bonadei | 92ea95e | 2017-09-15 04:47:31 | [diff] [blame] | 13 | #include "rtc_base/arraysize.h" |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 14 | |
| 15 | namespace rtc { |
| 16 | |
| 17 | // This implementation is based on the sample implementation in RFC 1952. |
| 18 | |
| 19 | // CRC32 polynomial, in reversed form. |
| 20 | // See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check |
Peter Boström | 0c4e06b | 2015-10-07 10:23:21 | [diff] [blame] | 21 | static const uint32_t kCrc32Polynomial = 0xEDB88320; |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 22 | |
Steve Anton | 0f1a7ba | 2019-05-15 23:22:38 | [diff] [blame] | 23 | static uint32_t* LoadCrc32Table() { |
| 24 | static uint32_t kCrc32Table[256]; |
tfarina | 5237aaf | 2015-11-11 07:44:30 | [diff] [blame] | 25 | for (uint32_t i = 0; i < arraysize(kCrc32Table); ++i) { |
Peter Boström | 0c4e06b | 2015-10-07 10:23:21 | [diff] [blame] | 26 | uint32_t c = i; |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 27 | for (size_t j = 0; j < 8; ++j) { |
| 28 | if (c & 1) { |
| 29 | c = kCrc32Polynomial ^ (c >> 1); |
| 30 | } else { |
| 31 | c >>= 1; |
| 32 | } |
| 33 | } |
| 34 | kCrc32Table[i] = c; |
| 35 | } |
Steve Anton | 0f1a7ba | 2019-05-15 23:22:38 | [diff] [blame] | 36 | return kCrc32Table; |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 37 | } |
| 38 | |
Peter Boström | 0c4e06b | 2015-10-07 10:23:21 | [diff] [blame] | 39 | uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) { |
Steve Anton | 0f1a7ba | 2019-05-15 23:22:38 | [diff] [blame] | 40 | static uint32_t* kCrc32Table = LoadCrc32Table(); |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 41 | |
Peter Boström | 0c4e06b | 2015-10-07 10:23:21 | [diff] [blame] | 42 | uint32_t c = start ^ 0xFFFFFFFF; |
| 43 | const uint8_t* u = static_cast<const uint8_t*>(buf); |
henrike@webrtc.org | f048872 | 2014-05-13 18:00:26 | [diff] [blame] | 44 | for (size_t i = 0; i < len; ++i) { |
| 45 | c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8); |
| 46 | } |
| 47 | return c ^ 0xFFFFFFFF; |
| 48 | } |
| 49 | |
| 50 | } // namespace rtc |