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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) return (~remainder); | |
28 | ||
29 | for (int byte = 0; byte < length; ++byte) { | |
30 | remainder ^= (message[byte] << 8); | |
31 | for (uint8_t bit = 8; bit > 0; --bit) { | |
32 | if (remainder & 0x8000) { | |
33 | remainder = (remainder << 1) ^ polynomial; | |
34 | } else { | |
35 | remainder = (remainder << 1); | |
36 | } | |
37 | } | |
38 | } | |
39 | return remainder; | |
40 | } | |
41 | ||
42 | uint16_t crc16_ccitt(uint8_t const *message, int length) { | |
43 | return crc16(message, length, 0xffff, 0x1021); | |
44 | } | |
45 | ||
46 | uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) { | |
47 | if (length == 0) return 0; | |
48 | uint32_t crc = 0, q = 0; | |
49 | uint8_t c; | |
50 | ||
51 | for (int i = 0; i < length; i++){ | |
52 | c = message[i]; | |
53 | q = (crc ^ c ) & 0xF; | |
54 | crc = (crc >> 4) ^ (q * 0x1081); | |
55 | q = (crc ^ (c >> 4)) & 0xF; | |
56 | crc = (crc >> 4) ^ (q * 0x1081); | |
57 | } | |
58 | return crc; | |
59 | } |