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# fastfouriertransformer.cpp Example File

demos/mobile/guitartuner/src/fastfouriertransformer.cpp

     /****************************************************************************
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     ** This file is part of the QtDeclarative module of the Qt Toolkit.
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     #include "fastfouriertransformer.h"
     #include "math.h"

     #define STIN  inline
     #define __STATIC

     #include "fftpack.c"

     // called by __ogg_fdrffti
     __STATIC void drfti1(int n, float *wa, int *ifac);
     void __ogg_fdrffti(int n, float *wsave, int *ifac);
     void __ogg_fdcosqi(int n, float *wsave, int *ifac);
     // called by drftf1
     STIN void dradf2(int ido,int l1,float *cc,float *ch,float *wa1);
     // called by drftf1
     STIN void dradf4(int ido,int l1,float *cc,float *ch,float *wa1,
             float *wa2,float *wa3);
     // called by drftf1
     STIN void dradfg(int ido,int ip,int l1,int idl1,float *cc,float *c1,
             float *c2,float *ch,float *ch2,float *wa);
     // called by drftf1
     STIN void drftf1(int n,float *c,float *ch,float *wa,int *ifac);
     void __ogg_fdrfftf(int n,float *r,float *wsave,int *ifac);
     STIN void dcsqf1(int n,float *x,float *w,float *xh,int *ifac);
     void __ogg_fdcosqf(int n,float *x,float *wsave,int *ifac);
     STIN void dradb2(int ido,int l1,float *cc,float *ch,float *wa1);
     STIN void dradb3(int ido,int l1,float *cc,float *ch,float *wa1,
                               float *wa2);
     STIN void dradb4(int ido,int l1,float *cc,float *ch,float *wa1,
             float *wa2,float *wa3);
     STIN void dradbg(int ido,int ip,int l1,int idl1,float *cc,float *c1,
                 float *c2,float *ch,float *ch2,float *wa);
     STIN void drftb1(int n, float *c, float *ch, float *wa, int *ifac);
     void __ogg_fdrfftb(int n, float *r, float *wsave, int *ifac);
     STIN void dcsqb1(int n,float *x,float *w,float *xh,int *ifac);
     void __ogg_fdcosqb(int n,float *x,float *wsave,int *ifac);

     FastFourierTransformer::FastFourierTransformer(QObject *parent) :
             QObject(parent),
             m_waveFloat(0),
             m_workingArray(0),
             m_ifac(0),
             m_last_n(-1)
     {
     }

     FastFourierTransformer::~FastFourierTransformer()
     {
         if (m_waveFloat != 0) {
             delete [] m_waveFloat;
         }
         if (m_workingArray != 0) {
            delete [] m_workingArray;
         }
         if (m_ifac != 0) {
             delete [] m_ifac;
         }
     }

     /**
       * Prepares the arrays to be of length n.
       */
     void FastFourierTransformer::reserve(int n)
     {
         Q_ASSERT(n>0);
         if (m_waveFloat != 0) {
             delete [] m_waveFloat;
         }
         if (m_workingArray != 0) {
            delete [] m_workingArray;
         }
         if (m_ifac != 0) {
             delete [] m_ifac;
         }
         m_workingArray = new float[2*n+15];
         m_waveFloat = new float[n];
         m_ifac = new int[n];
         __ogg_fdrffti(n, m_workingArray, m_ifac);
         m_last_n = n;
     }

     /**
       * Calculates the Fast Fourier Transformation (FFT).
       */
     void FastFourierTransformer::calculateFFT(QList<qint16> wave)
     {
         const int n = wave.size();
         if (m_last_n != n) {
             reserve(n);
         }
         for (int i = 0; i < n; i++) {
             m_waveFloat[i] = (float) wave.at(i);
         }

         __ogg_fdrfftf(n, m_waveFloat, m_workingArray, m_ifac);

     }

     /**
       * Returns the index which corresponds to the maximum density
       * of the FFT.
       */
     int FastFourierTransformer::getMaximumDensityIndex()
     {
         const int halfN = m_last_n / 2;
         float maxDensity = 0;
         int maxDensityIndex = 0;
         float densitySquared = 0.f;
         for (int k = 1; k < halfN; k++) {
             // Here, we calculate the frequency k/N.
             // k=1, the wave oscillation time is N, and the frequency
             //      is 1/sample.
             // k=2, the wave oscillation time is N/2, and the frequency
             //      is 2/sample.
             // k=3, the wave oscillation time is N/3, and the frequency
             //      is 3/sample.
             // Note, that the documentation is for Fortran, so indexes in the
             // documentation does not match.
             // The sine and cosine coefficients are obtained thus as follows:
             const float cosCoefficient = qAbs(m_waveFloat[2*k-1]);
             const float sinCoefficient = qAbs(m_waveFloat[2*k]);

             densitySquared = sinCoefficient*sinCoefficient + cosCoefficient*cosCoefficient;
             if (densitySquared > maxDensity) {
                 maxDensity = densitySquared;
                 maxDensityIndex = k;
             }
         }

         if (m_cutOffForDensitySquared < maxDensity) {
             return maxDensityIndex;
         }
         else {
             return -1;
         }
     }

     /**
       * Sets the cutoff density.
       */
     void FastFourierTransformer::setCutOffForDensity(float cutoff)
     {
         m_cutOffForDensitySquared = cutoff*cutoff;
     }