NucleoTNC/TNC/SymbolEvm.h

71 wiersze
1.4 KiB
C++

// Copyright 2020 Mobilinkd LLC.
#pragma once
#include "IirFilter.hpp"
#include <array>
#include <algorithm>
#include <numeric>
namespace mobilinkd
{
template <typename FloatType, size_t N>
struct SymbolEvm
{
using filter_type = tnc::IirFilter<N>;
using symbol_t = int;
using result_type = std::tuple<symbol_t, FloatType>;
filter_type filter_;
FloatType evm_ = 0.0;
SymbolEvm(const std::array<FloatType, N>& b, const std::array<FloatType, N>& a)
: filter_(b, a)
{}
FloatType evm() const { return evm_; }
/**
* Decode a normalized sample into a symbol. Symbols
* are decoded into +3, +1, -1, -3. If an erasure limit
* is set, symbols outside this limit are 'erased' and
* returned as 0.
*/
result_type operator()(FloatType sample)
{
symbol_t symbol;
FloatType evm;
sample = std::min(3.0f, std::max(-3.0f, sample));
if (sample > 2)
{
symbol = 3;
evm = (sample - 3) * 0.333333f;
}
else if (sample > 0)
{
symbol = 1;
evm = sample - 1;
}
else if (sample >= -2)
{
symbol = -1;
evm = sample + 1;
}
else
{
symbol = -3;
evm = (sample + 3) * 0.333333f;
}
evm_ = filter_(evm);
return std::make_tuple(symbol, evm);
}
};
} // mobilinkd