forked from ingeniamc/mcblib
-
Notifications
You must be signed in to change notification settings - Fork 0
/
mcb_crcccitt.c
162 lines (122 loc) · 4.86 KB
/
mcb_crcccitt.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
/*
* Library: libcrc
* File: src/crcccitt.c
* Author: Lammert Bies
*
* This file is licensed under the MIT License as stated below
*
* Copyright (c) 1999-2016 Lammert Bies
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
* Description
* -----------
* The module src/crcccitt.c contains routines which are used to calculate the
* CCITT CRC values of a string of bytes.
*/
#include <stdbool.h>
#include <stdlib.h>
#include "mcb_checksum.h"
static uint16_t crc_ccitt_generic( const unsigned char *input_str, size_t num_bytes, uint16_t start_value );
static void init_crcccitt_tab( void );
static bool crc_tabccitt_init = false;
static uint16_t crc_tabccitt[256];
/*
* uint16_t crc_xmodem( const unsigned char *input_str, size_t num_bytes );
*
* The function crc_xmodem() performs a one-pass calculation of an X-Modem CRC
* for a byte string that has been passed as a parameter.
*/
uint16_t crc_xmodem( const unsigned char *input_str, size_t num_bytes ) {
return crc_ccitt_generic( input_str, num_bytes, CRC_START_XMODEM );
} /* crc_xmodem */
/*
* uint16_t crc_ccitt_1d0f( const unsigned char *input_str, size_t num_bytes );
*
* The function crc_ccitt_1d0f() performs a one-pass calculation of the CCITT
* CRC for a byte string that has been passed as a parameter. The initial value
* 0x1d0f is used for the CRC.
*/
uint16_t crc_ccitt_1d0f( const unsigned char *input_str, size_t num_bytes ) {
return crc_ccitt_generic( input_str, num_bytes, CRC_START_CCITT_1D0F );
} /* crc_ccitt_1d0f */
/*
* uint16_t crc_ccitt_ffff( const unsigned char *input_str, size_t num_bytes );
*
* The function crc_ccitt_ffff() performs a one-pass calculation of the CCITT
* CRC for a byte string that has been passed as a parameter. The initial value
* 0xffff is used for the CRC.
*/
uint16_t crc_ccitt_ffff( const unsigned char *input_str, size_t num_bytes ) {
return crc_ccitt_generic( input_str, num_bytes, CRC_START_CCITT_FFFF );
} /* crc_ccitt_ffff */
/*
* static uint16_t crc_ccitt_generic( const unsigned char *input_str, size_t num_bytes, uint16_t start_value );
*
* The function crc_ccitt_generic() is a generic implementation of the CCITT
* algorithm for a one-pass calculation of the CRC for a byte string. The
* function accepts an initial start value for the crc.
*/
static uint16_t crc_ccitt_generic( const unsigned char *input_str, size_t num_bytes, uint16_t start_value ) {
uint16_t crc;
const unsigned char *ptr;
size_t a;
if ( ! crc_tabccitt_init ) init_crcccitt_tab();
crc = start_value;
ptr = input_str;
if ( ptr != NULL ) for (a=0; a<num_bytes; a++) {
crc = (crc << 8) ^ crc_tabccitt[ ((crc >> 8) ^ (uint16_t) *ptr++) & 0x00FF ];
}
return crc;
} /* crc_ccitt_generic */
/*
* uint16_t update_crc_ccitt( uint16_t crc, unsigned char c );
*
* The function update_crc_ccitt() calculates a new CRC-CCITT value based on
* the previous value of the CRC and the next byte of the data to be checked.
*/
uint16_t update_crc_ccitt( uint16_t crc, unsigned char c ) {
if ( ! crc_tabccitt_init ) init_crcccitt_tab();
return (crc << 8) ^ crc_tabccitt[ ((crc >> 8) ^ (uint16_t) c) & 0x00FF ];
} /* update_crc_ccitt */
/*
* static void init_crcccitt_tab( void );
*
* For optimal performance, the routine to calculate the CRC-CCITT uses a
* lookup table with pre-compiled values that can be directly applied in the
* XOR action. This table is created at the first call of the function by the
* init_crcccitt_tab() routine.
*/
static void init_crcccitt_tab( void ) {
uint16_t i;
uint16_t j;
uint16_t crc;
uint16_t c;
for (i=0; i<256; i++) {
crc = 0;
c = i << 8;
for (j=0; j<8; j++) {
if ( (crc ^ c) & 0x8000 ) crc = ( crc << 1 ) ^ CRC_POLY_CCITT;
else crc = crc << 1;
c = c << 1;
}
crc_tabccitt[i] = crc;
}
crc_tabccitt_init = true;
} /* init_crcccitt_tab */