FreeCalypso > hg > gsm-net-reveng

annotate trau-decode/crc8gen.c @ 14:98c0881c2af0

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tfo/find-is-hdr: move here from freecalypso-reveng This little program was developed in freecalypso-reveng Hg repository in 2023-03, when we didn't have a separate repository for network-side reverse eng, but now that we do have separate repositories for FreeCalypso (mobile side) vs network side reverse eng, move TFO RE work to the proper place.
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 24 May 2024 21:18:22 +0000
parents d9c095357c32
children
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1 /*! \file crc8gen.c
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2 * Osmocom generic CRC routines (for max 8 bits poly). */
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3 /*
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4 * Copyright (C) 2011 Sylvain Munaut <tnt@246tNt.com>
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5 *
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6 * All Rights Reserved
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7 *
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8 * SPDX-License-Identifier: GPL-2.0+
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9 *
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10 * This program is free software; you can redistribute it and/or modify
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11 * it under the terms of the GNU General Public License as published by
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12 * the Free Software Foundation; either version 2 of the License, or
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13 * (at your option) any later version.
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14 *
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15 * This program is distributed in the hope that it will be useful,
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16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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18 * GNU General Public License for more details.
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19 *
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20 * You should have received a copy of the GNU General Public License along
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21 * with this program; if not, write to the Free Software Foundation, Inc.,
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22 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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23 */
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24
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25 /*! \addtogroup crc
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26 * @{
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27 * Osmocom generic CRC routines (for max 8 bits poly).
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28 *
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29 * \file crc8gen.c.tpl */
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30
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31 #include <stdint.h>
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32 #include "osmo_bits.h"
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33
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34 /*! Compute the CRC value of a given array of hard-bits
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35 * \param[in] code The CRC code description to apply
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36 * \param[in] in Array of hard bits
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37 * \param[in] len Length of the array of hard bits
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38 * \returns The CRC value
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39 */
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40 uint8_t
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41 osmo_crc8gen_compute_bits(const struct osmo_crc8gen_code *code,
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42 const ubit_t *in, int len)
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43 {
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44 const uint8_t poly = code->poly;
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45 uint8_t crc = code->init;
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46 int i, n = code->bits-1;
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47
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48 for (i=0; i<len; i++) {
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49 uint8_t bit = in[i] & 1;
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50 crc ^= (bit << n);
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51 if (crc & ((uint8_t)1 << n)) {
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52 crc <<= 1;
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53 crc ^= poly;
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54 } else {
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55 crc <<= 1;
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56 }
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57 crc &= ((uint8_t)1 << code->bits) - 1;
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58 }
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59
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60 crc ^= code->remainder;
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61
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62 return crc;
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63 }
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64
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65
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66 /*! Checks the CRC value of a given array of hard-bits
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67 * \param[in] code The CRC code description to apply
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68 * \param[in] in Array of hard bits
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69 * \param[in] len Length of the array of hard bits
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70 * \param[in] crc_bits Array of hard bits with the alleged CRC
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71 * \returns 0 if CRC matches. 1 in case of error.
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72 *
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73 * The crc_bits array must have a length of code->len
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74 */
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75 int
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76 osmo_crc8gen_check_bits(const struct osmo_crc8gen_code *code,
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77 const ubit_t *in, int len, const ubit_t *crc_bits)
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78 {
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79 uint8_t crc;
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80 int i;
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81
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82 crc = osmo_crc8gen_compute_bits(code, in, len);
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83
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84 for (i=0; i<code->bits; i++)
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85 if (crc_bits[i] ^ ((crc >> (code->bits-i-1)) & 1))
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86 return 1;
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87
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88 return 0;
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89 }
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90
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91
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92 /*! Computes and writes the CRC value of a given array of bits
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93 * \param[in] code The CRC code description to apply
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94 * \param[in] in Array of hard bits
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95 * \param[in] len Length of the array of hard bits
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96 * \param[in] crc_bits Array of hard bits to write the computed CRC to
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97 *
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98 * The crc_bits array must have a length of code->len
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99 */
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100 void
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101 osmo_crc8gen_set_bits(const struct osmo_crc8gen_code *code,
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102 const ubit_t *in, int len, ubit_t *crc_bits)
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103 {
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104 uint8_t crc;
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105 int i;
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106
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107 crc = osmo_crc8gen_compute_bits(code, in, len);
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108
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109 for (i=0; i<code->bits; i++)
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110 crc_bits[i] = ((crc >> (code->bits-i-1)) & 1);
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111 }
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112
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113 /*! @} */
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114
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115 /* vim: set syntax=c: */