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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #include "rlz/lib/crc8.h" | |
6 | |
7 namespace { | |
8 | |
9 // The CRC lookup table used for ATM HES (Polynomial = 0x07). | |
10 // These are 256 unique 8-bit values. | |
11 const unsigned char kCrcTable[256] = { | |
12 0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15, | |
13 0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D, | |
14 0x70, 0x77, 0x7E, 0x79, 0x6C, 0x6B, 0x62, 0x65, | |
15 0x48, 0x4F, 0x46, 0x41, 0x54, 0x53, 0x5A, 0x5D, | |
16 0xE0, 0xE7, 0xEE, 0xE9, 0xFC, 0xFB, 0xF2, 0xF5, | |
17 0xD8, 0xDF, 0xD6, 0xD1, 0xC4, 0xC3, 0xCA, 0xCD, | |
18 0x90, 0x97, 0x9E, 0x99, 0x8C, 0x8B, 0x82, 0x85, | |
19 0xA8, 0xAF, 0xA6, 0xA1, 0xB4, 0xB3, 0xBA, 0xBD, | |
20 0xC7, 0xC0, 0xC9, 0xCE, 0xDB, 0xDC, 0xD5, 0xD2, | |
21 0xFF, 0xF8, 0xF1, 0xF6, 0xE3, 0xE4, 0xED, 0xEA, | |
22 0xB7, 0xB0, 0xB9, 0xBE, 0xAB, 0xAC, 0xA5, 0xA2, | |
23 0x8F, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9D, 0x9A, | |
24 0x27, 0x20, 0x29, 0x2E, 0x3B, 0x3C, 0x35, 0x32, | |
25 0x1F, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0D, 0x0A, | |
26 0x57, 0x50, 0x59, 0x5E, 0x4B, 0x4C, 0x45, 0x42, | |
27 0x6F, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7D, 0x7A, | |
28 0x89, 0x8E, 0x87, 0x80, 0x95, 0x92, 0x9B, 0x9C, | |
29 0xB1, 0xB6, 0xBF, 0xB8, 0xAD, 0xAA, 0xA3, 0xA4, | |
30 0xF9, 0xFE, 0xF7, 0xF0, 0xE5, 0xE2, 0xEB, 0xEC, | |
31 0xC1, 0xC6, 0xCF, 0xC8, 0xDD, 0xDA, 0xD3, 0xD4, | |
32 0x69, 0x6E, 0x67, 0x60, 0x75, 0x72, 0x7B, 0x7C, | |
33 0x51, 0x56, 0x5F, 0x58, 0x4D, 0x4A, 0x43, 0x44, | |
34 0x19, 0x1E, 0x17, 0x10, 0x05, 0x02, 0x0B, 0x0C, | |
35 0x21, 0x26, 0x2F, 0x28, 0x3D, 0x3A, 0x33, 0x34, | |
36 0x4E, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5C, 0x5B, | |
37 0x76, 0x71, 0x78, 0x7F, 0x6A, 0x6D, 0x64, 0x63, | |
38 0x3E, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2C, 0x2B, | |
39 0x06, 0x01, 0x08, 0x0F, 0x1A, 0x1D, 0x14, 0x13, | |
40 0xAE, 0xA9, 0xA0, 0xA7, 0xB2, 0xB5, 0xBC, 0xBB, | |
41 0x96, 0x91, 0x98, 0x9F, 0x8A, 0x8D, 0x84, 0x83, | |
42 0xDE, 0xD9, 0xD0, 0xD7, 0xC2, 0xC5, 0xCC, 0xCB, | |
43 0xE6, 0xE1, 0xE8, 0xEF, 0xFA, 0xFD, 0xF4, 0xF3 | |
44 }; | |
45 | |
46 } // namespace anonymous | |
47 | |
48 | |
49 namespace rlz_lib { | |
50 | |
51 bool Crc8::Generate(const unsigned char *data, int length, | |
52 unsigned char* check_sum) { | |
53 if (!check_sum) | |
54 return false; | |
55 | |
56 *check_sum = 0; | |
57 if (!data) | |
58 return false; | |
59 | |
60 // The inital and final constants are as used in the ATM HEC. | |
61 static const unsigned char kInitial = 0x00; | |
62 static const unsigned char kFinal = 0x55; | |
63 unsigned char crc = kInitial; | |
64 for (int i = 0; i < length; ++i) { | |
65 crc = kCrcTable[(data[i] ^ crc) & 0xFFU]; | |
66 } | |
67 | |
68 *check_sum = crc ^ kFinal; | |
69 return true; | |
70 } | |
71 | |
72 bool Crc8::Verify(const unsigned char* data, int length, | |
73 unsigned char check_sum, bool* matches) { | |
74 if (!matches) | |
75 return false; | |
76 | |
77 *matches = false; | |
78 if (!data) | |
79 return false; | |
80 | |
81 unsigned char calculated_crc; | |
82 if (!Generate(data, length, &calculated_crc)) | |
83 return false; | |
84 | |
85 *matches = check_sum == calculated_crc; | |
86 | |
87 return true; | |
88 } | |
89 | |
90 } // namespace rlz_lib | |
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