feat: integrate RTL-TCP server support

android/app/src/main/cpp/dsp/fftnr.cpp

@@ -0,0 +1,148 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2023 Edouard Griffiths, F4EXB <f4exb06@gmail.com>               //
+//                                                                               //
+// Helper class for noise reduction                                              //
+//                                                                               //
+// 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/>.          //
+///////////////////////////////////////////////////////////////////////////////////
+
+#include <algorithm>
+#include <numeric>
+
+#include <QDebug>
+
+#include "fftnr.h"
+
+FFTNoiseReduction::FFTNoiseReduction(int len) :
+    m_flen(len)
+{
+    m_scheme = SchemeAverage;
+    m_mags = new float[m_flen];
+    m_tmp = new float[m_flen];
+    m_aboveAvgFactor = 1.0;
+    m_sigmaFactor = 1.0;
+    m_nbPeaks = m_flen;
+}
+
+FFTNoiseReduction::~FFTNoiseReduction()
+{
+    delete[] m_mags;
+    delete[] m_tmp;
+}
+
+void FFTNoiseReduction::init()
+{
+    std::fill(m_mags, m_mags + m_flen, 0);
+    std::fill(m_tmp, m_tmp + m_flen, 0);
+    m_magAvg = 0;
+}
+
+void FFTNoiseReduction::push(cmplx data, int index)
+{
+    m_mags[index] = std::abs(data);
+
+    if ((m_scheme == SchemeAverage) || (m_scheme == SchemeAvgStdDev)) {
+        m_magAvg += m_mags[index];
+    }
+}
+
+void FFTNoiseReduction::calc()
+{
+    if (m_scheme == SchemeAverage)
+    {
+        m_magAvg /= m_flen;
+        m_magAvg = m_expFilter.push(m_magAvg);
+    }
+    if (m_scheme == SchemeAvgStdDev)
+    {
+        m_magAvg /= m_flen;
+
+        auto variance_func = [this](float accumulator, const float& val) {
+            return accumulator + ((val - m_magAvg)*(val - m_magAvg) / (m_flen - 1));
+        };
+
+        float var = std::accumulate(m_mags, m_mags + m_flen, 0.0, variance_func);
+        m_magThr = (m_sigmaFactor/2.0)*std::sqrt(var) + m_magAvg;
+        m_magThr = m_expFilter.push(m_magThr);
+    }
+    else if (m_scheme == SchemePeaks)
+    {
+        std::copy(m_mags, m_mags + m_flen, m_tmp);
+        std::sort(m_tmp, m_tmp + m_flen);
+        m_magThr = m_tmp[m_flen - m_nbPeaks];
+    }
+}
+
+bool FFTNoiseReduction::cut(int index)
+{
+    if (m_scheme == SchemeAverage)
+    {
+        return m_mags[index] < m_aboveAvgFactor * m_magAvg;
+    }
+    else if ((m_scheme == SchemePeaks) || (m_scheme == SchemeAvgStdDev))
+    {
+        return m_mags[index] < m_magThr;
+    }
+
+    return false;
+}
+
+void FFTNoiseReduction::setScheme(Scheme scheme)
+{
+    if (m_scheme != scheme) {
+        m_expFilter.reset();
+    }
+
+    m_scheme = scheme;
+}
+
+FFTNoiseReduction::ExponentialFilter::ExponentialFilter()
+{
+    m_alpha = 1.0;
+    m_init = true;
+}
+
+float FFTNoiseReduction::ExponentialFilter::push(float newValue)
+{
+    if (m_init)
+    {
+        m_prev = newValue;
+        m_init = false;
+    }
+
+    if (m_alpha == 1.0)
+    {
+        m_prev = newValue;
+        return newValue;
+    }
+    else
+    {
+        float result = m_alpha*m_prev + (1.0 - m_alpha)*newValue;
+        m_prev = result;
+        return result;
+    }
+}
+
+void FFTNoiseReduction::ExponentialFilter::reset()
+{
+    m_init = true;
+}
+
+void FFTNoiseReduction::ExponentialFilter::setAlpha(float alpha)
+{
+    m_alpha = alpha < 0.0f ? 0.0f : alpha > 1.0f ? 1.0f : alpha;
+    qDebug("FFTNoiseReduction::ExponentialFilter::setAlpha: %f", m_alpha);
+    m_init = true;
+}
+