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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 }
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