portapack-mayhem/firmware/common/crc.hpp
Jared Boone a366b3ac4f CRC class.
Has some more efficient code, commented out because I was having trouble getting it to work. However, it may have been due to the particular data I was trying to decode and CRC-validate.
2015-11-06 13:49:59 -08:00

105 lines
2.4 KiB
C++

/*
* Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
*
* This file is part of PortaPack.
*
* 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 2, 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; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef __CRC_H__
#define __CRC_H__
#include <cstddef>
#include <cstdint>
template<typename T>
class CRC {
public:
constexpr CRC(
const T polynomial/*,
const T initial*/
) : polynomial { polynomial }/*,
initial { initial }*/
{
// CRC LSB must always be 1
}
/*
template<typename U>
T calculate(const U& bits, const size_t length) {
if( length > bits.size() ) {
// Exception.
return 0;
}
T crc = 0;
for(size_t i=0; i<length; i++) {
crc = feed_bit(crc, bits[i]);
}
return crc;
}
*/
T calculate_byte(const T crc_in, const uint8_t data) {
/* Inspired by
* http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code
*/
T remainder = crc_in;
remainder ^= data << (width() - 8);
for(size_t bit=8; bit>0; --bit) {
if( remainder & top_bit() ) {
remainder = (remainder << 1) ^ polynomial;
} else {
remainder = (remainder << 1);
}
}
return remainder;
}
/*
T calculate(const uint8_t* const data, const size_t length) {
T remainder = initial;
for(size_t byte=0; byte<length; ++byte) {
remainder = calculate_byte(remainder, data[byte]);
}
return remainder;
}
*/
private:
const T polynomial;
// const T initial;
static constexpr size_t width() {
return 8 * sizeof(T);
}
static constexpr T top_bit() {
return 1U << (width() - 1);
}
/*
T feed_bit(const T crc_in, const uint_fast8_t bit) {
T crc_out = crc_in ^ (bit & 1);
if( crc_in & top_bit() ) {
return ((crc_in << 1) | (bit & 1)) ^ polynomial;
} else {
return (crc_in << 1) | (bit & 1);
}
}
*/
};
#endif/*__CRC_H__*/