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85 lines
1.7 KiB
C++
85 lines
1.7 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 <tuple>
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namespace modemm17
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{
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template <size_t N>
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struct SymbolEvm
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{
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using filter_type = BaseIirFilter<N>;
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using symbol_t = int;
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using result_type = std::tuple<symbol_t, float>;
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filter_type filter_;
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float erasure_limit_;
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float evm_ = 0.0;
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SymbolEvm(filter_type&& filter, float erasure_limit = 0.0) :
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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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float 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()(float sample)
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{
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symbol_t symbol;
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float evm;
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sample = std::min(3.0f, std::max(-3.0f, 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 (std::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 <size_t N>
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SymbolEvm<N> makeSymbolEvm(
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BaseIirFilter<N>&& filter,
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float erasure_limit = 0.0f
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)
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{
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return std::move(SymbolEvm<N>(std::move(filter), erasure_limit));
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}
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} // modemm17
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