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comparison libutil/crc8gen.c @ 194:05d01e810217

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libutil: add TFO message gen function based on Osmocom crc8gen
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 17 Mar 2023 16:52:21 -0800
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193:1f9a6cede2c5 194:05d01e810217
1 /*! \file crc8gen.c
2 * Osmocom generic CRC routines (for max 8 bits poly). */
3 /*
4 * Copyright (C) 2011 Sylvain Munaut <tnt@246tNt.com>
5 *
6 * All Rights Reserved
7 *
8 * SPDX-License-Identifier: GPL-2.0+
9 *
10 * This program is free software; you can redistribute it and/or modify
11 * it under the terms of the GNU General Public License as published by
12 * the Free Software Foundation; either version 2 of the License, or
13 * (at your option) any later version.
14 *
15 * This program is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 * GNU General Public License for more details.
19 *
20 * You should have received a copy of the GNU General Public License along
21 * with this program; if not, write to the Free Software Foundation, Inc.,
22 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
23 */
24
25 /*! \addtogroup crc
26 * @{
27 * Osmocom generic CRC routines (for max 8 bits poly).
28 *
29 * \file crc8gen.c.tpl */
30
31 #include <stdint.h>
32 #include "osmo_bits.h"
33
34 /*! Compute the CRC value of a given array of hard-bits
35 * \param[in] code The CRC code description to apply
36 * \param[in] in Array of hard bits
37 * \param[in] len Length of the array of hard bits
38 * \returns The CRC value
39 */
40 uint8_t
41 osmo_crc8gen_compute_bits(const struct osmo_crc8gen_code *code,
42 const ubit_t *in, int len)
43 {
44 const uint8_t poly = code->poly;
45 uint8_t crc = code->init;
46 int i, n = code->bits-1;
47
48 for (i=0; i<len; i++) {
49 uint8_t bit = in[i] & 1;
50 crc ^= (bit << n);
51 if (crc & ((uint8_t)1 << n)) {
52 crc <<= 1;
53 crc ^= poly;
54 } else {
55 crc <<= 1;
56 }
57 crc &= ((uint8_t)1 << code->bits) - 1;
58 }
59
60 crc ^= code->remainder;
61
62 return crc;
63 }
64
65
66 /*! Checks the CRC value of a given array of hard-bits
67 * \param[in] code The CRC code description to apply
68 * \param[in] in Array of hard bits
69 * \param[in] len Length of the array of hard bits
70 * \param[in] crc_bits Array of hard bits with the alleged CRC
71 * \returns 0 if CRC matches. 1 in case of error.
72 *
73 * The crc_bits array must have a length of code->len
74 */
75 int
76 osmo_crc8gen_check_bits(const struct osmo_crc8gen_code *code,
77 const ubit_t *in, int len, const ubit_t *crc_bits)
78 {
79 uint8_t crc;
80 int i;
81
82 crc = osmo_crc8gen_compute_bits(code, in, len);
83
84 for (i=0; i<code->bits; i++)
85 if (crc_bits[i] ^ ((crc >> (code->bits-i-1)) & 1))
86 return 1;
87
88 return 0;
89 }
90
91
92 /*! Computes and writes the CRC value of a given array of bits
93 * \param[in] code The CRC code description to apply
94 * \param[in] in Array of hard bits
95 * \param[in] len Length of the array of hard bits
96 * \param[in] crc_bits Array of hard bits to write the computed CRC to
97 *
98 * The crc_bits array must have a length of code->len
99 */
100 void
101 osmo_crc8gen_set_bits(const struct osmo_crc8gen_code *code,
102 const ubit_t *in, int len, ubit_t *crc_bits)
103 {
104 uint8_t crc;
105 int i;
106
107 crc = osmo_crc8gen_compute_bits(code, in, len);
108
109 for (i=0; i<code->bits; i++)
110 crc_bits[i] = ((crc >> (code->bits-i-1)) & 1);
111 }
112
113 /*! @} */
114
115 /* vim: set syntax=c: */