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