kopia lustrzana https://github.com/mobilinkd/m17-cxx-demod
84 wiersze
1.9 KiB
C++
84 wiersze
1.9 KiB
C++
// Copyright 2020 Mobilinkd LLC.
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#pragma once
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#include "IirFilter.h"
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#include <array>
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#include <algorithm>
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#include <numeric>
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#include <optional>
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#include <tuple>
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namespace mobilinkd
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{
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template <typename FloatType, size_t N>
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struct SymbolEvm
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{
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using filter_type = BaseIirFilter<FloatType, N>;
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using symbol_t = int;
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using result_type = std::tuple<symbol_t, FloatType>;
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filter_type filter_;
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std::optional<FloatType> erasure_limit_;
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FloatType evm_ = 0.0;
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SymbolEvm(filter_type&& filter, std::optional<FloatType> erasure_limit = std::nullopt)
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: filter_(std::forward<filter_type>(filter))
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, erasure_limit_(erasure_limit)
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{}
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FloatType evm() const { return evm_; }
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/**
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* Decode a normalized sample into a symbol. Symbols
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* are decoded into +3, +1, -1, -3. If an erasure limit
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* is set, symbols outside this limit are 'erased' and
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* returned as 0.
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*/
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result_type operator()(FloatType sample)
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{
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symbol_t symbol;
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FloatType evm;
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sample = std::min(3.0, std::max(-3.0, sample));
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if (sample > 2)
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{
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symbol = 3;
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evm = (sample - 3) * 0.333333;
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}
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else if (sample > 0)
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{
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symbol = 1;
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evm = sample - 1;
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}
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else if (sample >= -2)
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{
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symbol = -1;
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evm = sample + 1;
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}
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else
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{
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symbol = -3;
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evm = (sample + 3) * 0.333333;
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}
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if (erasure_limit_ and (abs(evm) > *erasure_limit_)) symbol = 0;
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evm_ = filter_(evm);
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return std::make_tuple(symbol, evm);
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}
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};
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template <typename FloatType, size_t N>
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SymbolEvm<FloatType, N> makeSymbolEvm(
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BaseIirFilter<FloatType, N>&& filter, std::optional<FloatType> erasure_limit = std::nullopt)
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{
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return std::move(SymbolEvm<FloatType, N>(std::move(filter), erasure_limit));
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}
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} // mobilinkd
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