| 1 | //----------------------------------------------------------------------------- |
| 2 | // This code is licensed to you under the terms of the GNU GPL, version 2 or, |
| 3 | // at your option, any later version. See the LICENSE.txt file for the text of |
| 4 | // the license. |
| 5 | //----------------------------------------------------------------------------- |
| 6 | // CRC16 |
| 7 | //----------------------------------------------------------------------------- |
| 8 | |
| 9 | #include "crc16.h" |
| 10 | |
| 11 | |
| 12 | unsigned short update_crc16( unsigned short crc, unsigned char c ) |
| 13 | { |
| 14 | unsigned short i, v, tcrc = 0; |
| 15 | |
| 16 | v = (crc ^ c) & 0xff; |
| 17 | for (i = 0; i < 8; i++) { |
| 18 | tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1; |
| 19 | v >>= 1; |
| 20 | } |
| 21 | |
| 22 | return ((crc >> 8) ^ tcrc)&0xffff; |
| 23 | } |
| 24 | |
| 25 | uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) { |
| 26 | |
| 27 | if (length == 0) |
| 28 | return (~remainder); |
| 29 | |
| 30 | for (int byte = 0; byte < length; ++byte) { |
| 31 | remainder ^= (message[byte] << 8); |
| 32 | for (uint8_t bit = 8; bit > 0; --bit) { |
| 33 | if (remainder & 0x8000) { |
| 34 | remainder = (remainder << 1) ^ polynomial; |
| 35 | } else { |
| 36 | remainder = (remainder << 1); |
| 37 | } |
| 38 | } |
| 39 | } |
| 40 | return remainder; |
| 41 | } |
| 42 | |
| 43 | uint16_t crc16_ccitt(uint8_t const *message, int length) { |
| 44 | return crc16(message, length, 0xffff, 0x1021); |
| 45 | } |