portapack-mayhem/firmware/common/crc.hpp
Jared Boone df825807d6 CRC: Rearrange public methods to reduce user error.
If you can access process_bits() without considering RevIn value, you will likely not get the CRC value you're expecting! Put RevIn check where it belongs, in process_bits().
2016-07-05 11:57:57 -07:00

196 lines
4.8 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>
#include <limits>
#include <array>
/* Inspired by
* http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code
*
* ...then munged into a simplified implementation of boost::crc_basic and
* boost::crc_optimal.
* http://www.boost.org/doc/libs/release/libs/crc/
*
* Copyright 2001, 2004 Daryle Walker. Use, modification, and distribution are
* subject to the Boost Software License, Version 1.0. (See accompanying file
* LICENSE_1_0.txt or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
*
*/
template<size_t Width, bool RevIn = false, bool RevOut = false>
class CRC {
public:
using value_type = uint32_t;
constexpr CRC(
const value_type truncated_polynomial,
const value_type initial_remainder = 0,
const value_type final_xor_value = 0
) : truncated_polynomial { truncated_polynomial },
initial_remainder { initial_remainder },
final_xor_value { final_xor_value },
remainder { initial_remainder }
{
}
value_type get_initial_remainder() const {
return initial_remainder;
}
void reset(value_type new_initial_remainder) {
remainder = new_initial_remainder;
}
void reset() {
remainder = initial_remainder;
}
void process_bit(bool bit) {
remainder ^= (bit ? top_bit() : 0U);
const auto do_poly_div = static_cast<bool>(remainder & top_bit());
remainder <<= 1;
if( do_poly_div ) {
remainder ^= truncated_polynomial;
}
}
void process_bits(value_type bits, size_t bit_count) {
if( RevIn ) {
process_bits_lsb_first(bits, bit_count);
} else {
process_bits_msb_first(bits, bit_count);
}
}
void process_byte(const uint8_t byte) {
process_bits(byte, 8);
}
void process_bytes(const void* const data, const size_t length) {
const uint8_t* const p = reinterpret_cast<const uint8_t*>(data);
for(size_t i=0; i<length; i++) {
process_byte(p[i]);
}
}
template<size_t N>
void process_bytes(const std::array<uint8_t, N>& data) {
process_bytes(data.data(), data.size());
}
value_type checksum() const {
return ((RevOut ? reflect(remainder) : remainder) ^ final_xor_value) & mask();
}
private:
const value_type truncated_polynomial;
const value_type initial_remainder;
const value_type final_xor_value;
value_type remainder;
static constexpr size_t width() {
return Width;
}
static constexpr value_type top_bit() {
return 1U << (width() - 1);
}
static constexpr value_type mask() {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wshift-count-overflow"
return (~(~(0UL) << width()));
#pragma GCC diagnostic pop
}
static value_type reflect(value_type x) {
value_type reflection = 0;
for(size_t i=0; i<width(); ++i) {
reflection <<= 1;
reflection |= (x & 1);
x >>= 1;
}
return reflection;
}
void process_bits_msb_first(value_type bits, size_t bit_count) {
constexpr auto digits = std::numeric_limits<value_type>::digits;
constexpr auto mask = static_cast<value_type>(1) << (digits - 1);
bits <<= (std::numeric_limits<value_type>::digits - bit_count);
for(size_t i=bit_count; i>0; --i, bits <<= 1) {
process_bit(static_cast<bool>(bits & mask));
}
}
void process_bits_lsb_first(value_type bits, size_t bit_count) {
for(size_t i=bit_count; i>0; --i, bits >>= 1) {
process_bit(static_cast<bool>(bits & 0x01));
}
}
};
class Adler32 {
public:
void feed(const uint8_t v) {
feed_one(v);
}
void feed(const void* const data, const size_t n) {
const uint8_t* const p = reinterpret_cast<const uint8_t*>(data);
for(size_t i=0; i<n; i++) {
feed_one(p[i]);
}
}
template<typename T>
void feed(const T& a) {
feed(a.data(), sizeof(T));
}
std::array<uint8_t, 4> bytes() const {
return {
static_cast<uint8_t>((b >> 8) & 0xff),
static_cast<uint8_t>((b >> 0) & 0xff),
static_cast<uint8_t>((a >> 8) & 0xff),
static_cast<uint8_t>((a >> 0) & 0xff)
};
}
private:
static constexpr uint32_t mod = 65521;
uint32_t a { 1 };
uint32_t b { 0 };
void feed_one(const uint8_t c) {
a = (a + c) % mod;
b = (b + a) % mod;
}
};
#endif/*__CRC_H__*/