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sdrangel/sdrbase/dsp/iirfilter.h
2020-11-04 21:51:55 +01:00

159 lines
4.0 KiB
C++

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