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/**
* Copyright (C) 2019 Johan van der Vyver
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "voltronic_crc.h"
#define IS_INTEGER_EQUAL(_ch__a_, _ch__b_) \
((_ch__a_) == (_ch__b_))
#define IS_RESERVED_BYTE(_ch_) ( \
IS_INTEGER_EQUAL((_ch_), 0x28) || \
IS_INTEGER_EQUAL((_ch_), 0x0D) || \
IS_INTEGER_EQUAL((_ch_), 0x0A))
#define CRC_SIZE \
(sizeof(voltronic_crc_t))
int write_voltronic_crc(
const voltronic_crc_t crc,
char* cstring_buffer) {
if (cstring_buffer != 0) {
unsigned char* buffer =
(unsigned char*) cstring_buffer;
buffer[0] = (crc >> 8) & 0xFF;
buffer[1] = crc & 0xFF;
}
return CRC_SIZE;
}
voltronic_crc_t read_voltronic_crc(
const char* cstring_buffer) {
const unsigned char* buffer =
(const unsigned char*) cstring_buffer;
voltronic_crc_t crc = 0;
crc |= (voltronic_crc_t) buffer[0] << 8;
crc |= (voltronic_crc_t) buffer[1];
return crc;
}
voltronic_crc_t calculate_voltronic_crc(
const char* cstring_buffer,
size_t buffer_length) {
voltronic_crc_t crc = 0;
if (buffer_length > 0) {
static const voltronic_crc_t crc_table[16] = {
0x0000, 0x1021, 0x2042, 0x3063,
0x4084, 0x50A5, 0x60C6, 0x70E7,
0x8108, 0x9129, 0xA14A, 0xB16B,
0xC18C, 0xD1AD, 0xE1CE, 0xF1EF
};
const unsigned char* buffer =
(const unsigned char*) cstring_buffer;
unsigned char byte;
do {
byte = *buffer;
crc = crc_table[(crc >> 12) ^ (byte >> 4)] ^ (crc << 4);
crc = crc_table[(crc >> 12) ^ (byte & 0x0F)] ^ (crc << 4);
buffer += sizeof(unsigned char);
} while(--buffer_length);
byte = crc;
if (IS_RESERVED_BYTE(byte)) {
crc += 1;
}
byte = crc >> 8;
if (IS_RESERVED_BYTE(byte)) {
crc += 1 << 8;
}
}
return crc;
}
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