[175] | 1 | /*
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| 2 | * Copyright (c) 2005, Swedish Institute of Computer Science
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| 3 | * All rights reserved.
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| 4 | *
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| 5 | * Redistribution and use in source and binary forms, with or without
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| 6 | * modification, are permitted provided that the following conditions
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| 7 | * are met:
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| 8 | * 1. Redistributions of source code must retain the above copyright
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| 9 | * notice, this list of conditions and the following disclaimer.
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| 10 | * 2. Redistributions in binary form must reproduce the above copyright
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| 11 | * notice, this list of conditions and the following disclaimer in the
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| 12 | * documentation and/or other materials provided with the distribution.
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| 13 | * 3. Neither the name of the Institute nor the names of its contributors
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| 14 | * may be used to endorse or promote products derived from this software
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| 15 | * without specific prior written permission.
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| 16 | *
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| 17 | * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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| 18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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| 19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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| 20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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| 21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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| 22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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| 23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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| 24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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| 25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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| 26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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| 27 | * SUCH DAMAGE.
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| 28 | *
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| 29 | * This file is part of the Contiki operating system.
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| 30 | *
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| 31 | */
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| 32 |
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| 33 | /** \addtogroup crc16
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| 34 | * @{ */
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| 35 |
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| 36 | /**
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| 37 | * \file
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| 38 | * Implementation of the CRC16 calculcation
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| 39 | * \author
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| 40 | * Adam Dunkels <adam@sics.se>
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| 41 | *
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| 42 | */
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| 43 |
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| 44 | /* CITT CRC16 polynomial ^16 + ^12 + ^5 + 1 */
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| 45 | /*---------------------------------------------------------------------------*/
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| 46 | unsigned short
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| 47 | crc16_add(unsigned char b, unsigned short acc)
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| 48 | {
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| 49 | /*
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| 50 | acc = (unsigned char)(acc >> 8) | (acc << 8);
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| 51 | acc ^= b;
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| 52 | acc ^= (unsigned char)(acc & 0xff) >> 4;
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| 53 | acc ^= (acc << 8) << 4;
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| 54 | acc ^= ((acc & 0xff) << 4) << 1;
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| 55 | */
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| 56 |
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| 57 | acc ^= b;
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| 58 | acc = (acc >> 8) | (acc << 8);
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| 59 | acc ^= (acc & 0xff00) << 4;
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| 60 | acc ^= (acc >> 8) >> 4;
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| 61 | acc ^= (acc & 0xff00) >> 5;
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| 62 | return acc;
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| 63 | }
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| 64 | /*---------------------------------------------------------------------------*/
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| 65 | unsigned short
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| 66 | crc16_data(const unsigned char *data, int len, unsigned short acc)
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| 67 | {
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| 68 | int i;
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| 69 |
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| 70 | for(i = 0; i < len; ++i) {
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| 71 | acc = crc16_add(*data, acc);
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| 72 | ++data;
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| 73 | }
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| 74 | return acc;
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| 75 | }
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| 76 | /*---------------------------------------------------------------------------*/
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| 77 |
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| 78 | /** @} */
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