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159 lines
4.0 KiB
C++
159 lines
4.0 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2017 F4EXB //
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// written by Edouard Griffiths //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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/**
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* IIR filter
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* See: https://cdn.mikroe.com/ebooks/img/8/2016/02/digital-filter-design-chapter-03-image-2-9.gif
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*/
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#ifndef SDRBASE_DSP_IIRFILTER_H_
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#define SDRBASE_DSP_IIRFILTER_H_
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#include <stdint.h>
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#include <string.h>
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template <typename Type, uint32_t Order> class IIRFilter
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{
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public:
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IIRFilter(const Type *a, const Type *b);
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~IIRFilter();
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void setCoeffs(const Type *a, const Type *b);
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Type run(const Type& sample);
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private:
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Type *m_a;
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Type *m_b;
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Type *m_x;
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Type *m_y;
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};
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template <typename Type> class IIRFilter<Type, 2>
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{
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public:
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IIRFilter(const Type *a, const Type *b);
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~IIRFilter();
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void setCoeffs(const Type *a, const Type *b);
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Type run(const Type& sample);
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private:
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Type m_a[3];
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Type m_b[3];
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Type m_x[2];
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Type m_y[2];
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};
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template <typename Type, uint32_t Order>
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IIRFilter<Type, Order>::IIRFilter(const Type *a, const Type *b)
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{
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m_a = new Type[Order+1];
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m_b = new Type[Order+1];
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m_x = new Type[Order];
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m_y = new Type[Order];
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setCoeffs(a, b);
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}
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template <typename Type, uint32_t Order>
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IIRFilter<Type, Order>::~IIRFilter()
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{
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delete[] m_y;
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delete[] m_x;
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delete[] m_b;
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delete[] m_a;
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}
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template <typename Type, uint32_t Order>
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void IIRFilter<Type, Order>::setCoeffs(const Type *a, const Type *b)
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{
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memcpy(m_a, b, (Order+1)*sizeof(Type));
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memcpy(m_b, a, (Order+1)*sizeof(Type));
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for (uint32_t i = 0; i < Order; i++)
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{
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m_x[i] = 0;
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m_y[i] = 0;
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}
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}
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template <typename Type, uint32_t Order>
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Type IIRFilter<Type, Order>::run(const Type& sample)
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{
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Type y = m_b[0] * sample;
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for (uint32_t i = Order; i > 0; i--)
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{
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y += m_b[i] * m_x[i-1] + m_a[i] * m_y[i-1];
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if (i > 1) // shift
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{
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m_x[i-1] = m_x[i-2];
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m_y[i-1] = m_y[i-2];
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}
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}
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// last shift
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m_x[0] = sample;
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m_y[0] = y;
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return y;
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}
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template <typename Type>
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IIRFilter<Type, 2>::IIRFilter(const Type *a, const Type *b)
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{
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setCoeffs(a, b);
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}
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template <typename Type>
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IIRFilter<Type, 2>::~IIRFilter()
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{
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}
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template <typename Type>
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void IIRFilter<Type, 2>::setCoeffs(const Type *a, const Type *b)
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{
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m_a[0] = a[0];
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m_a[1] = a[1];
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m_a[2] = a[2];
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m_b[0] = b[0];
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m_b[1] = b[1];
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m_b[2] = b[2];
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m_x[0] = 0;
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m_x[1] = 0;
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m_y[0] = 0;
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m_y[1] = 0;
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}
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template <typename Type>
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Type IIRFilter<Type, 2>::run(const Type& sample)
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{
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Type y = m_b[0]*sample + m_b[1]*m_x[0] + m_b[2]*m_x[1] + m_a[1]*m_y[0] + m_a[2]*m_y[1]; // this is y[n]
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m_x[1] = m_x[0];
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m_x[0] = sample;
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m_y[1] = m_y[0];
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m_y[0] = y;
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return y;
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}
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#endif /* SDRBASE_DSP_IIRFILTER_H_ */
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