| 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 | unsigned short update_crc16( unsigned short crc, unsigned char c ) |
| 12 | { |
| 13 | unsigned short i, v, tcrc = 0; |
| 14 | |
| 15 | v = (crc ^ c) & 0xff; |
| 16 | for (i = 0; i < 8; i++) { |
| 17 | tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1; |
| 18 | v >>= 1; |
| 19 | } |
| 20 | |
| 21 | return ((crc >> 8) ^ tcrc)&0xffff; |
| 22 | } |
| 23 | |
| 24 | uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) { |
| 25 | |
| 26 | if (length == 0) return (~remainder); |
| 27 | |
| 28 | for (int byte = 0; byte < length; ++byte) { |
| 29 | remainder ^= (message[byte] << 8); |
| 30 | for (uint8_t bit = 8; bit > 0; --bit) { |
| 31 | if (remainder & 0x8000) { |
| 32 | remainder = (remainder << 1) ^ polynomial; |
| 33 | } else { |
| 34 | remainder = (remainder << 1); |
| 35 | } |
| 36 | } |
| 37 | } |
| 38 | return remainder; |
| 39 | } |
| 40 | |
| 41 | uint16_t crc16_ccitt(uint8_t const *message, int length) { |
| 42 | return crc16(message, length, 0xffff, 0x1021); |
| 43 | } |
| 44 | |
| 45 | uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) { |
| 46 | return bit_reverse_uint16(crc16(message, length, 0x0000, 0x1021)); |
| 47 | } |
| 48 | |
| 49 | uint16_t bit_reverse_uint16 (uint16_t value) { |
| 50 | const uint16_t mask0 = 0x5555; |
| 51 | const uint16_t mask1 = 0x3333; |
| 52 | const uint16_t mask2 = 0x0F0F; |
| 53 | const uint16_t mask3 = 0x00FF; |
| 54 | |
| 55 | value = (((~mask0) & value) >> 1) | ((mask0 & value) << 1); |
| 56 | value = (((~mask1) & value) >> 2) | ((mask1 & value) << 2); |
| 57 | value = (((~mask2) & value) >> 4) | ((mask2 & value) << 4); |
| 58 | value = (((~mask3) & value) >> 8) | ((mask3 & value) << 8); |
| 59 | |
| 60 | return value; |
| 61 | } |