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52 lines
1.3 KiB
C++
52 lines
1.3 KiB
C++
/*
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Fs/4 Complex down conversion
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Copyright 2019 Ahmet Inan <inan@aicodix.de>
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*/
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#pragma once
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#include "filter.hh"
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#include "window.hh"
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namespace DSP {
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template <typename TYPE, int TAPS>
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class CDC
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{
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static_assert((TAPS-1) % 4 == 0, "TAPS-1 not divisible by four");
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typedef TYPE complex_type;
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typedef typename TYPE::value_type value_type;
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value_type real[(TAPS-1)/4];
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value_type imag[(TAPS-1)/2];
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value_type imco[(TAPS-1)/4];
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value_type reco;
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bool sign;
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public:
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CDC(value_type a = value_type(2)) : sign(false)
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{
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Kaiser<value_type> win(a);
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LowPass2<value_type> hbf(1, 4);
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reco = win((TAPS-1)/2, TAPS) * hbf((TAPS-1)/2, TAPS);
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for (int i = 0; i < (TAPS-1)/4; ++i)
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imco[i] = win(2*i+(TAPS-1)/2+1, TAPS) * hbf(2*i+(TAPS-1)/2+1, TAPS);
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}
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complex_type operator()(value_type in0, value_type in1)
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{
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sign = !sign;
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value_type re = reco * real[0];
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for (int i = 0; i < (TAPS-1)/4-1; ++i)
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real[i] = real[i+1];
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real[(TAPS-1)/4-1] = sign ? in1 : -in1;
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for (int i = 0; i < (TAPS-1)/2-1; ++i)
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imag[i] = imag[i+1];
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imag[(TAPS-1)/2-1] = sign ? in0 : -in0;
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value_type im = imco[0] * (imag[(TAPS-1)/4-1] + imag[(TAPS-1)/4]);
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for (int i = 1; i < (TAPS-1)/4; ++i)
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im += imco[i] * (imag[(TAPS-1)/4-1-i] + imag[(TAPS-1)/4+i]);
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return complex_type(re, im);
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}
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};
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}
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