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 91
