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81 lines
2.7 KiB
C
81 lines
2.7 KiB
C
/*
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* Copyright (c) 2005, Swedish Institute of Computer Science
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This file is part of the Contiki operating system.
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*
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* @(#)$Id: crc16.c,v 1.2 2008/07/07 23:24:36 adamdunkels Exp $
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*/
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/** \addtogroup crc16
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* @{ */
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/**
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* \file
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* Implementation of the CRC16 calculcation
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* \author
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* Adam Dunkels <adam@sics.se>
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*
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*/
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/* CITT CRC16 polynomial ^16 + ^12 + ^5 + 1 */
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/*---------------------------------------------------------------------------*/
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unsigned short
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crc16_add(unsigned char b, unsigned short acc)
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{
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/*
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acc = (unsigned char)(acc >> 8) | (acc << 8);
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acc ^= b;
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acc ^= (unsigned char)(acc & 0xff) >> 4;
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acc ^= (acc << 8) << 4;
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acc ^= ((acc & 0xff) << 4) << 1;
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*/
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acc ^= b;
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acc = (acc >> 8) | (acc << 8);
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acc ^= (acc & 0xff00) << 4;
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acc ^= (acc >> 8) >> 4;
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acc ^= (acc & 0xff00) >> 5;
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return acc;
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}
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/*---------------------------------------------------------------------------*/
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unsigned short
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crc16_data(unsigned char *data, int len, unsigned short acc)
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{
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int i;
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unsigned short crc = 0;
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for(i = 0; i < len; ++i) {
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crc = crc16_add(*data, crc);
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++data;
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}
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return crc;
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}
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/*---------------------------------------------------------------------------*/
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/** @} */
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