Contiki-NG
crc16.c
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1 /*
2  * Copyright (c) 2005, Swedish Institute of Computer Science
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
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8  * 1. Redistributions of source code must retain the above copyright
9  * notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  * notice, this list of conditions and the following disclaimer in the
12  * documentation and/or other materials provided with the distribution.
13  * 3. Neither the name of the Institute nor the names of its contributors
14  * may be used to endorse or promote products derived from this software
15  * without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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28  *
29  * This file is part of the Contiki operating system.
30  *
31  */
32 
33 /** \addtogroup crc16
34  * @{ */
35 
36 /**
37  * \file
38  * Implementation of the CRC16 calculcation
39  * \author
40  * Adam Dunkels <adam@sics.se>
41  *
42  */
43 
44 /* CITT CRC16 polynomial ^16 + ^12 + ^5 + 1 */
45 /*---------------------------------------------------------------------------*/
46 unsigned short
47 crc16_add(unsigned char b, unsigned short acc)
48 {
49  /*
50  acc = (unsigned char)(acc >> 8) | (acc << 8);
51  acc ^= b;
52  acc ^= (unsigned char)(acc & 0xff) >> 4;
53  acc ^= (acc << 8) << 4;
54  acc ^= ((acc & 0xff) << 4) << 1;
55  */
56 
57  acc ^= b;
58  acc = (acc >> 8) | (acc << 8);
59  acc ^= (acc & 0xff00) << 4;
60  acc ^= (acc >> 8) >> 4;
61  acc ^= (acc & 0xff00) >> 5;
62  return acc;
63 }
64 /*---------------------------------------------------------------------------*/
65 unsigned short
66 crc16_data(const unsigned char *data, int len, unsigned short acc)
67 {
68  int i;
69 
70  for(i = 0; i < len; ++i) {
71  acc = crc16_add(*data, acc);
72  ++data;
73  }
74  return acc;
75 }
76 /*---------------------------------------------------------------------------*/
77 
78 /** @} */
unsigned short crc16_add(unsigned char b, unsigned short acc)
Update an accumulated CRC16 checksum with one byte.
Definition: crc16.c:47
unsigned short crc16_data(const unsigned char *data, int len, unsigned short acc)
Calculate the CRC16 over a data area.
Definition: crc16.c:66