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https://github.com/eried/portapack-mayhem.git
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a366b3ac4f
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.
105 lines
2.4 KiB
C++
105 lines
2.4 KiB
C++
/*
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* Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
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*
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* This file is part of PortaPack.
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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 2, or (at your option)
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* 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; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifndef __CRC_H__
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#define __CRC_H__
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#include <cstddef>
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#include <cstdint>
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template<typename T>
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class CRC {
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public:
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constexpr CRC(
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const T polynomial/*,
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const T initial*/
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) : polynomial { polynomial }/*,
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initial { initial }*/
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{
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// CRC LSB must always be 1
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}
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/*
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template<typename U>
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T calculate(const U& bits, const size_t length) {
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if( length > bits.size() ) {
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// Exception.
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return 0;
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}
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T crc = 0;
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for(size_t i=0; i<length; i++) {
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crc = feed_bit(crc, bits[i]);
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}
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return crc;
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}
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*/
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T calculate_byte(const T crc_in, const uint8_t data) {
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/* Inspired by
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* http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code
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*/
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T remainder = crc_in;
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remainder ^= data << (width() - 8);
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for(size_t bit=8; bit>0; --bit) {
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if( remainder & top_bit() ) {
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remainder = (remainder << 1) ^ polynomial;
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} else {
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remainder = (remainder << 1);
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}
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}
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return remainder;
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}
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/*
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T calculate(const uint8_t* const data, const size_t length) {
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T remainder = initial;
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for(size_t byte=0; byte<length; ++byte) {
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remainder = calculate_byte(remainder, data[byte]);
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}
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return remainder;
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}
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*/
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private:
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const T polynomial;
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// const T initial;
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static constexpr size_t width() {
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return 8 * sizeof(T);
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}
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static constexpr T top_bit() {
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return 1U << (width() - 1);
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}
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/*
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T feed_bit(const T crc_in, const uint_fast8_t bit) {
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T crc_out = crc_in ^ (bit & 1);
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if( crc_in & top_bit() ) {
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return ((crc_in << 1) | (bit & 1)) ^ polynomial;
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} else {
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return (crc_in << 1) | (bit & 1);
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}
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}
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*/
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};
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#endif/*__CRC_H__*/
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