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crc16.c

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00001 /*
00002  * Copyright (c) 2005, Swedish Institute of Computer Science
00003  * All rights reserved. 
00004  *
00005  * Redistribution and use in source and binary forms, with or without 
00006  * modification, are permitted provided that the following conditions 
00007  * are met: 
00008  * 1. Redistributions of source code must retain the above copyright 
00009  *    notice, this list of conditions and the following disclaimer. 
00010  * 2. Redistributions in binary form must reproduce the above copyright 
00011  *    notice, this list of conditions and the following disclaimer in the 
00012  *    documentation and/or other materials provided with the distribution. 
00013  * 3. Neither the name of the Institute nor the names of its contributors 
00014  *    may be used to endorse or promote products derived from this software 
00015  *    without specific prior written permission. 
00016  *
00017  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND 
00018  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
00019  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
00020  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE 
00021  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 
00022  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 
00023  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
00024  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 
00025  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 
00026  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 
00027  * SUCH DAMAGE. 
00028  *
00029  * This file is part of the Contiki operating system.
00030  *
00031  * @(#)$Id: crc16.c,v 1.1 2006/06/17 22:41:17 adamdunkels Exp $
00032  */
00033 
00034 /** \addtogroup crc16
00035  * @{ */
00036 
00037 /**
00038  * \file
00039  *         Implementation of the CRC16 calculcation
00040  * \author
00041  *         Adam Dunkels <adam@sics.se>
00042  * 
00043  */
00044 
00045 /* CITT CRC16 polynomial ^16 + ^12 + ^5 + 1 */
00046 /*---------------------------------------------------------------------------*/
00047 unsigned short
00048 crc16_add(unsigned char b, unsigned short acc)
00049 {
00050   /*
00051     acc  = (unsigned char)(acc >> 8) | (acc << 8);
00052     acc ^= b;
00053     acc ^= (unsigned char)(acc & 0xff) >> 4;
00054     acc ^= (acc << 8) << 4;
00055     acc ^= ((acc & 0xff) << 4) << 1;
00056   */
00057 
00058   acc ^= b;
00059   acc  = (acc >> 8) | (acc << 8);
00060   acc ^= (acc & 0xff00) << 4;
00061   acc ^= (acc >> 8) >> 4;
00062   acc ^= (acc & 0xff00) >> 5;
00063   return acc;
00064 }
00065 /*---------------------------------------------------------------------------*/
00066 
00067 /** @} */

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