blob: 42f86cb268ae9a01f25ea90282035a35638e7e99 [file] [log] [blame]
henrike@webrtc.orgf0488722014-05-13 18:00:261/*
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 Bonadei92ea95e2017-09-15 04:47:3111#include "rtc_base/crc32.h"
henrike@webrtc.orgf0488722014-05-13 18:00:2612
Mirko Bonadei92ea95e2017-09-15 04:47:3113#include "rtc_base/arraysize.h"
henrike@webrtc.orgf0488722014-05-13 18:00:2614
15namespace 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 Boström0c4e06b2015-10-07 10:23:2121static const uint32_t kCrc32Polynomial = 0xEDB88320;
henrike@webrtc.orgf0488722014-05-13 18:00:2622
Steve Anton0f1a7ba2019-05-15 23:22:3823static uint32_t* LoadCrc32Table() {
24 static uint32_t kCrc32Table[256];
tfarina5237aaf2015-11-11 07:44:3025 for (uint32_t i = 0; i < arraysize(kCrc32Table); ++i) {
Peter Boström0c4e06b2015-10-07 10:23:2126 uint32_t c = i;
henrike@webrtc.orgf0488722014-05-13 18:00:2627 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 Anton0f1a7ba2019-05-15 23:22:3836 return kCrc32Table;
henrike@webrtc.orgf0488722014-05-13 18:00:2637}
38
Peter Boström0c4e06b2015-10-07 10:23:2139uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) {
Steve Anton0f1a7ba2019-05-15 23:22:3840 static uint32_t* kCrc32Table = LoadCrc32Table();
henrike@webrtc.orgf0488722014-05-13 18:00:2641
Peter Boström0c4e06b2015-10-07 10:23:2142 uint32_t c = start ^ 0xFFFFFFFF;
43 const uint8_t* u = static_cast<const uint8_t*>(buf);
henrike@webrtc.orgf0488722014-05-13 18:00:2644 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