Calculate the iButton/Maxim crc for a give bytearray @param data bytearray of data to calculate a CRC for @return Single byte CRC calculated from the data.
(data)
| 1 | def CalculateCRC(data): |
| 2 | """ |
| 3 | Calculate the iButton/Maxim crc for a give bytearray |
| 4 | @param data bytearray of data to calculate a CRC for |
| 5 | @return Single byte CRC calculated from the data. |
| 6 | """ |
| 7 | # CRC table from http://forum.sparkfun.com/viewtopic.php?p=51145 |
| 8 | crctab = [ |
| 9 | 0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65, |
| 10 | 157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220, |
| 11 | 35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93, 3, 128, 222, 60, 98, |
| 12 | 190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255, |
| 13 | 70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7, |
| 14 | 219, 133, 103, 57, 186, 228, 6, 88, 25, 71, 165, 251, 120, 38, 196, 154, |
| 15 | 101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36, |
| 16 | 248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185, |
| 17 | 140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205, |
| 18 | 17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80, |
| 19 | 175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238, |
| 20 | 50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115, |
| 21 | 202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234, 105, 55, 213, 139, |
| 22 | 87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22, |
| 23 | 233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168, |
| 24 | 116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53 |
| 25 | ] |
| 26 | |
| 27 | data_bytes = bytearray(data) |
| 28 | |
| 29 | val = 0 |
| 30 | for x in data_bytes: |
| 31 | val = crctab[val ^ x] |
| 32 | return val |