Contiki 2.5
crc16.c
Go to the documentation of this file.
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
7  * are met:
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
18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20  * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27  * SUCH DAMAGE.
28  *
29  * This file is part of the Contiki operating system.
30  *
31  * @(#)$Id: crc16.c,v 1.4 2009/05/14 12:05:04 nvt-se Exp $
32  */
33 
34 /** \addtogroup crc16
35  * @{ */
36 
37 /**
38  * \file
39  * Implementation of the CRC16 calculcation
40  * \author
41  * Adam Dunkels <adam@sics.se>
42  *
43  */
44 
45 /* CITT CRC16 polynomial ^16 + ^12 + ^5 + 1 */
46 /*---------------------------------------------------------------------------*/
47 unsigned short
48 crc16_add(unsigned char b, unsigned short acc)
49 {
50  /*
51  acc = (unsigned char)(acc >> 8) | (acc << 8);
52  acc ^= b;
53  acc ^= (unsigned char)(acc & 0xff) >> 4;
54  acc ^= (acc << 8) << 4;
55  acc ^= ((acc & 0xff) << 4) << 1;
56  */
57 
58  acc ^= b;
59  acc = (acc >> 8) | (acc << 8);
60  acc ^= (acc & 0xff00) << 4;
61  acc ^= (acc >> 8) >> 4;
62  acc ^= (acc & 0xff00) >> 5;
63  return acc;
64 }
65 /*---------------------------------------------------------------------------*/
66 unsigned short
67 crc16_data(const unsigned char *data, int len, unsigned short acc)
68 {
69  int i;
70 
71  for(i = 0; i < len; ++i) {
72  acc = crc16_add(*data, acc);
73  ++data;
74  }
75  return acc;
76 }
77 /*---------------------------------------------------------------------------*/
78 
79 /** @} */