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sdrangel/modemm17/Golay24.h

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// Copyright 2020 Rob Riggs <rob@mobilinkd.com>
// All rights reserved.
#pragma once
#include <array>
#include <cstdint>
#include <algorithm>
#include <utility>
#include "export.h"
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namespace modemm17 {
// Parts are adapted from:
// http://aqdi.com/articles/using-the-golay-error-detection-and-correction-code-3/
namespace Golay24_detail
{
// Need a constexpr sort.
// https://stackoverflow.com/a/40030044/854133
template<class T>
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static void swap(T& l, T& r)
{
T tmp = std::move(l);
l = std::move(r);
r = std::move(tmp);
}
template <typename T, size_t N>
struct array
{
constexpr T& operator[](size_t i) {
return arr[i];
}
constexpr const T& operator[](size_t i) const {
return arr[i];
}
constexpr const T* begin() const {
return arr;
}
constexpr const T* end() const {
return arr + N;
}
T arr[N];
};
template <typename T, size_t N>
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static void sort_impl(array<T, N> &array, size_t left, size_t right)
{
if (left < right)
{
size_t m = left;
for (size_t i = left + 1; i<right; i++)
if (array[i]<array[left])
swap(array[++m], array[i]);
swap(array[left], array[m]);
sort_impl(array, left, m);
sort_impl(array, m + 1, right);
}
}
template <typename T, size_t N>
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static array<T, N> sort(array<T, N> array)
{
auto sorted = array;
sort_impl(sorted, 0, N);
return sorted;
}
} // Golay24_detail
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struct MODEMM17_API Golay24
{
#pragma pack(push, 1)
struct SyndromeMapEntry
{
uint32_t a{0};
uint16_t b{0};
};
#pragma pack(pop)
static const uint16_t POLY = 0xC75;
static const size_t LUT_SIZE = 2048;
static std::array<SyndromeMapEntry, LUT_SIZE> LUT;
Golay24();
static uint32_t encode23(uint16_t data);
static uint32_t encode24(uint16_t data);
static bool decode(uint32_t input, uint32_t& output);
private:
static bool parity(uint32_t codeword);
static SyndromeMapEntry makeSyndromeMapEntry(uint64_t val);
static uint32_t syndrome(uint32_t codeword);
static uint64_t makeSME(uint64_t syndrome, uint32_t bits);
static std::array<SyndromeMapEntry, LUT_SIZE> make_lut();
};
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} // modemm17