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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 | 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 | } |