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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