1 /*
2 * Copyright (c) 2016, The OpenThread Authors.
3 * All rights reserved.
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 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * 3. Neither the name of the copyright holder nor the
13 * names of its contributors may 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 COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
20 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 /**
30 * @file
31 * This file implements CRC16 computations.
32 */
33
34 #include "crc.hpp"
35
36 namespace ot {
37
FeedByte(uint8_t aByte)38 template <typename UintType> UintType CrcCalculator<UintType>::FeedByte(uint8_t aByte)
39 {
40 static constexpr UintType kMsb = kIsUint16 ? (1u << 15) : (1u << 31);
41 static constexpr uint8_t kBitShift = kIsUint16 ? 8 : 24;
42
43 mCrc ^= (static_cast<UintType>(aByte) << kBitShift);
44
45 for (uint8_t i = 8; i > 0; i--)
46 {
47 bool msbIsSet = (mCrc & kMsb);
48
49 mCrc <<= 1;
50
51 if (msbIsSet)
52 {
53 mCrc ^= mPolynomial;
54 }
55 }
56
57 return mCrc;
58 }
59
FeedBytes(const void * aBytes,uint16_t aLength)60 template <typename UintType> UintType CrcCalculator<UintType>::FeedBytes(const void *aBytes, uint16_t aLength)
61 {
62 const uint8_t *bytes = reinterpret_cast<const uint8_t *>(aBytes);
63
64 while (aLength-- > 0)
65 {
66 FeedByte(*bytes++);
67 }
68
69 return mCrc;
70 }
71
72 template <typename UintType>
Feed(const Message & aMessage,const OffsetRange & aOffsetRange)73 UintType CrcCalculator<UintType>::Feed(const Message &aMessage, const OffsetRange &aOffsetRange)
74 {
75 uint16_t length = aOffsetRange.GetLength();
76 Message::Chunk chunk;
77
78 aMessage.GetFirstChunk(aOffsetRange.GetOffset(), length, chunk);
79
80 while (chunk.GetLength() > 0)
81 {
82 FeedBytes(chunk.GetBytes(), chunk.GetLength());
83 aMessage.GetNextChunk(length, chunk);
84 }
85
86 return mCrc;
87 }
88
89 template class CrcCalculator<uint16_t>;
90 template class CrcCalculator<uint32_t>;
91
92 } // namespace ot
93