mirror of
https://github.com/TomHarte/CLK.git
synced 2024-11-18 17:06:15 +00:00
111 lines
2.8 KiB
C++
111 lines
2.8 KiB
C++
//
|
|
// CRC.hpp
|
|
// Clock Signal
|
|
//
|
|
// Created by Thomas Harte on 18/09/2016.
|
|
// Copyright 2016 Thomas Harte. All rights reserved.
|
|
//
|
|
|
|
#ifndef CRC_hpp
|
|
#define CRC_hpp
|
|
|
|
#include <cstdint>
|
|
#include <vector>
|
|
|
|
namespace CRC {
|
|
|
|
/*! Provides a class capable of generating a CRC from source data. */
|
|
template <typename T, T reset_value, T xor_output, bool reflect_input, bool reflect_output> class Generator {
|
|
public:
|
|
/*!
|
|
Instantiates a CRC16 that will compute the CRC16 specified by the supplied
|
|
@c polynomial and @c reset_value.
|
|
*/
|
|
Generator(T polynomial): value_(reset_value) {
|
|
const T top_bit = T(~(T(~0) >> 1));
|
|
for(int c = 0; c < 256; c++) {
|
|
T shift_value = static_cast<T>(c << multibyte_shift);
|
|
for(int b = 0; b < 8; b++) {
|
|
T exclusive_or = (shift_value&top_bit) ? polynomial : 0;
|
|
shift_value = static_cast<T>(shift_value << 1) ^ exclusive_or;
|
|
}
|
|
xor_table[c] = shift_value;
|
|
}
|
|
}
|
|
|
|
/// Resets the CRC to the reset value.
|
|
void reset() { value_ = reset_value; }
|
|
|
|
/// Updates the CRC to include @c byte.
|
|
void add(uint8_t byte) {
|
|
if(reflect_input) byte = reverse_byte(byte);
|
|
value_ = static_cast<T>((value_ << 8) ^ xor_table[(value_ >> multibyte_shift) ^ byte]);
|
|
}
|
|
|
|
/// @returns The current value of the CRC.
|
|
inline T get_value() const {
|
|
T result = value_^xor_output;
|
|
if(reflect_output) {
|
|
T reflected_output = 0;
|
|
for(std::size_t c = 0; c < sizeof(T); ++c) {
|
|
reflected_output = T(reflected_output << 8) | T(reverse_byte(result & 0xff));
|
|
result >>= 8;
|
|
}
|
|
return reflected_output;
|
|
}
|
|
return result;
|
|
}
|
|
|
|
/// Sets the current value of the CRC.
|
|
inline void set_value(T value) { value_ = value; }
|
|
|
|
/*!
|
|
A compound for:
|
|
|
|
reset()
|
|
[add all data from @c data]
|
|
get_value()
|
|
*/
|
|
T compute_crc(const std::vector<uint8_t> &data) {
|
|
reset();
|
|
for(const auto &byte: data) add(byte);
|
|
return get_value();
|
|
}
|
|
|
|
private:
|
|
static constexpr int multibyte_shift = (sizeof(T) * 8) - 8;
|
|
T xor_table[256];
|
|
T value_;
|
|
|
|
constexpr uint8_t reverse_byte(uint8_t byte) const {
|
|
return
|
|
((byte & 0x80) ? 0x01 : 0x00) |
|
|
((byte & 0x40) ? 0x02 : 0x00) |
|
|
((byte & 0x20) ? 0x04 : 0x00) |
|
|
((byte & 0x10) ? 0x08 : 0x00) |
|
|
((byte & 0x08) ? 0x10 : 0x00) |
|
|
((byte & 0x04) ? 0x20 : 0x00) |
|
|
((byte & 0x02) ? 0x40 : 0x00) |
|
|
((byte & 0x01) ? 0x80 : 0x00);
|
|
}
|
|
};
|
|
|
|
/*!
|
|
Provides a generator of 16-bit CCITT CRCs, which amongst other uses are
|
|
those used by the FM and MFM disk encodings.
|
|
*/
|
|
struct CCITT: public Generator<uint16_t, 0xffff, 0x0000, false, false> {
|
|
CCITT() : Generator(0x1021) {}
|
|
};
|
|
|
|
/*!
|
|
Provides a generator of "standard 32-bit" CRCs.
|
|
*/
|
|
struct CRC32: public Generator<uint32_t, 0xffffffff, 0xffffffff, true, true> {
|
|
CRC32() : Generator(0x04c11db7) {}
|
|
};
|
|
|
|
}
|
|
|
|
#endif /* CRC_hpp */
|