nes-proj/core/lib/crc16.c

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/*
* Copyright (c) 2005, Swedish Institute of Computer Science
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This file is part of the Contiki operating system.
*
*/
/** \addtogroup crc16
* @{ */
/**
* \file
* Implementation of the CRC16 calculcation
* \author
* Adam Dunkels <adam@sics.se>
*
*/
/* CITT CRC16 polynomial ^16 + ^12 + ^5 + 1 */
/*---------------------------------------------------------------------------*/
unsigned short
crc16_add(unsigned char b, unsigned short acc)
{
/*
acc = (unsigned char)(acc >> 8) | (acc << 8);
acc ^= b;
acc ^= (unsigned char)(acc & 0xff) >> 4;
acc ^= (acc << 8) << 4;
acc ^= ((acc & 0xff) << 4) << 1;
*/
acc ^= b;
acc = (acc >> 8) | (acc << 8);
acc ^= (acc & 0xff00) << 4;
acc ^= (acc >> 8) >> 4;
acc ^= (acc & 0xff00) >> 5;
return acc;
}
/*---------------------------------------------------------------------------*/
unsigned short
2008-08-26 21:46:06 +00:00
crc16_data(const unsigned char *data, int len, unsigned short acc)
{
int i;
for(i = 0; i < len; ++i) {
acc = crc16_add(*data, acc);
++data;
}
return acc;
}
/*---------------------------------------------------------------------------*/
/** @} */