mirror of
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147 lines
5.3 KiB
C++
147 lines
5.3 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2018 F4EXB //
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// written by Edouard Griffiths //
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// //
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// Float half-band FIR based interpolator and decimator //
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// This is the double buffer variant //
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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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// //
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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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#ifndef INCLUDE_INTHALFBANDFILTER_DBF_H
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#define INCLUDE_INTHALFBANDFILTER_DBF_H
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#include <stdint.h>
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#include "dsp/dsptypes.h"
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#include "dsp/hbfiltertraits.h"
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#include "export.h"
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template<typename AccuType, typename SampleType, uint32_t HBFilterOrder>
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class SDRBASE_API IntHalfbandFilterDBF {
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public:
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IntHalfbandFilterDBF();
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void myDecimate(AccuType x1, AccuType y1, AccuType *x2, AccuType *y2)
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{
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storeSample(x1, y1);
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advancePointer();
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storeSample(*x2, *y2);
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doFIR(x2, y2);
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advancePointer();
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}
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/** Optimized upsampler by 2 not calculating FIR with inserted null samples */
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void myInterpolate(qint32 *x1, qint32 *y1, qint32 *x2, qint32 *y2)
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{
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// insert sample into ring double buffer
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m_samplesDB[m_ptr][0] = *x1;
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m_samplesDB[m_ptr][1] = *y1;
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m_samplesDB[m_ptr + HBFIRFilterTraits<HBFilterOrder>::hbOrder/2][0] = *x1;
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m_samplesDB[m_ptr + HBFIRFilterTraits<HBFilterOrder>::hbOrder/2][1] = *y1;
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// advance pointer
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if (m_ptr < (HBFIRFilterTraits<HBFilterOrder>::hbOrder/2) - 1) {
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m_ptr++;
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} else {
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m_ptr = 0;
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}
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// first output sample calculated with the middle peak
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*x1 = m_samplesDB[m_ptr + (HBFIRFilterTraits<HBFilterOrder>::hbOrder/4) - 1][0];
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*y1 = m_samplesDB[m_ptr + (HBFIRFilterTraits<HBFilterOrder>::hbOrder/4) - 1][1];
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// second sample calculated with the filter
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doInterpolateFIR(x2, y2);
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}
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protected:
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SampleType m_samplesDB[2*(HBFIRFilterTraits<HBFilterOrder>::hbOrder - 1)][2]; // double buffer technique
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int m_ptr;
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int m_size;
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int m_state;
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void storeSample(AccuType x, AccuType y)
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{
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m_samplesDB[m_ptr][0] = x;
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m_samplesDB[m_ptr][1] = y;
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m_samplesDB[m_ptr + m_size][0] = x;
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m_samplesDB[m_ptr + m_size][1] = y;
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}
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void advancePointer()
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{
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m_ptr = m_ptr + 1 < m_size ? m_ptr + 1: 0;
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}
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void doFIR(AccuType *x, AccuType *y)
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{
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int a = m_ptr + m_size; // tip pointer
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int b = m_ptr + 1; // tail pointer
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AccuType iAcc = 0;
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AccuType qAcc = 0;
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for (int i = 0; i < HBFIRFilterTraits<HBFilterOrder>::hbOrder / 4; i++)
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{
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iAcc += (m_samplesDB[a][0] + m_samplesDB[b][0]) * HBFIRFilterTraits<HBFilterOrder>::hbCoeffsF[i];
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qAcc += (m_samplesDB[a][1] + m_samplesDB[b][1]) * HBFIRFilterTraits<HBFilterOrder>::hbCoeffsF[i];
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a -= 2;
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b += 2;
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}
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iAcc += m_samplesDB[b-1][0] / 2.0;
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qAcc += m_samplesDB[b-1][1] / 2.0;
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*x = iAcc; // HB_SHIFT incorrect do not loose the gained bit
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*y = qAcc;
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}
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void doInterpolateFIR(qint32 *x, qint32 *y)
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{
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qint16 a = m_ptr;
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qint16 b = m_ptr + (HBFIRFilterTraits<HBFilterOrder>::hbOrder / 2) - 1;
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// go through samples in buffer
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AccuType iAcc = 0;
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AccuType qAcc = 0;
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for (int i = 0; i < HBFIRFilterTraits<HBFilterOrder>::hbOrder / 4; i++)
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{
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iAcc += (m_samplesDB[a][0] + m_samplesDB[b][0]) * HBFIRFilterTraits<HBFilterOrder>::hbCoeffsF[i];
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qAcc += (m_samplesDB[a][1] + m_samplesDB[b][1]) * HBFIRFilterTraits<HBFilterOrder>::hbCoeffsF[i];
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a++;
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b--;
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}
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*x = iAcc * SDR_RX_SCALED;
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*y = qAcc * SDR_RX_SCALED;
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}
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};
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template<typename AccuType, typename SampleType, uint32_t HBFilterOrder>
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IntHalfbandFilterDBF<AccuType, SampleType, HBFilterOrder>::IntHalfbandFilterDBF()
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{
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m_size = HBFIRFilterTraits<HBFilterOrder>::hbOrder - 1;
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for (int i = 0; i < m_size; i++)
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{
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m_samplesDB[i][0] = 0;
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m_samplesDB[i][1] = 0;
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}
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m_ptr = 0;
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m_state = 0;
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}
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#endif // INCLUDE_INTHALFBANDFILTER_DBF_H
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