comparison dsp/transforms/FFT.cpp @ 225:49844bc8a895

* Queen Mary C++ DSP library

+/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
+
+/*
+    QM DSP Library
+
+    Centre for Digital Music, Queen Mary, University of London.
+    This file is based on Don Cross's public domain FFT implementation.
+*/
+
+#include "FFT.h"
+#include <cmath>
+
+//////////////////////////////////////////////////////////////////////
+// Construction/Destruction
+//////////////////////////////////////////////////////////////////////
+
+FFT::FFT()
+{
+
+}
+
+FFT::~FFT()
+{
+
+}
+
+void FFT::process(unsigned int p_nSamples, bool p_bInverseTransform, double *p_lpRealIn, double *p_lpImagIn, double *p_lpRealOut, double *p_lpImagOut)
+{
+
+    if(!p_lpRealIn || !p_lpRealOut || !p_lpImagOut) return;
+
+
+    unsigned int NumBits;
+    unsigned int i, j, k, n;
+    unsigned int BlockSize, BlockEnd;
+
+    double angle_numerator = 2.0 * M_PI;
+    double tr, ti;
+
+    if( !isPowerOfTwo(p_nSamples) )
+    {
+	return;
+    }
+
+    if( p_bInverseTransform ) angle_numerator = -angle_numerator;
+
+    NumBits = numberOfBitsNeeded ( p_nSamples );
+
+
+    for( i=0; i < p_nSamples; i++ )
+    {
+	j = reverseBits ( i, NumBits );
+	p_lpRealOut[j] = p_lpRealIn[i];
+	p_lpImagOut[j] = (p_lpImagIn == 0) ? 0.0 : p_lpImagIn[i];
+    }
+
+
+    BlockEnd = 1;
+    for( BlockSize = 2; BlockSize <= p_nSamples; BlockSize <<= 1 )
+    {
+	double delta_angle = angle_numerator / (double)BlockSize;
+	double sm2 = -sin ( -2 * delta_angle );
+	double sm1 = -sin ( -delta_angle );
+	double cm2 = cos ( -2 * delta_angle );
+	double cm1 = cos ( -delta_angle );
+	double w = 2 * cm1;
+	double ar[3], ai[3];
+
+	for( i=0; i < p_nSamples; i += BlockSize )
+	{
+
+	    ar[2] = cm2;
+	    ar[1] = cm1;
+
+	    ai[2] = sm2;
+	    ai[1] = sm1;
+
+	    for ( j=i, n=0; n < BlockEnd; j++, n++ )
+	    {
+
+		ar[0] = w*ar[1] - ar[2];
+		ar[2] = ar[1];
+		ar[1] = ar[0];
+
+		ai[0] = w*ai[1] - ai[2];
+		ai[2] = ai[1];
+		ai[1] = ai[0];
+
+		k = j + BlockEnd;
+		tr = ar[0]*p_lpRealOut[k] - ai[0]*p_lpImagOut[k];
+		ti = ar[0]*p_lpImagOut[k] + ai[0]*p_lpRealOut[k];
+
+		p_lpRealOut[k] = p_lpRealOut[j] - tr;
+		p_lpImagOut[k] = p_lpImagOut[j] - ti;
+
+		p_lpRealOut[j] += tr;
+		p_lpImagOut[j] += ti;
+
+	    }
+	}
+
+	BlockEnd = BlockSize;
+
+    }
+
+
+    if( p_bInverseTransform )
+    {
+	double denom = (double)p_nSamples;
+
+	for ( i=0; i < p_nSamples; i++ )
+	{
+	    p_lpRealOut[i] /= denom;
+	    p_lpImagOut[i] /= denom;
+	}
+    }
+}
+
+bool FFT::isPowerOfTwo(unsigned int p_nX)
+{
+    if( p_nX < 2 ) return false;
+
+    if( p_nX & (p_nX-1) ) return false;
+
+    return true;
+}
+
+unsigned int FFT::numberOfBitsNeeded(unsigned int p_nSamples)
+{	
+    int i;
+
+    if( p_nSamples < 2 )
+    {
+	return 0;
+    }
+
+    for ( i=0; ; i++ )
+    {
+	if( p_nSamples & (1 << i) ) return i;
+    }
+}
+
+unsigned int FFT::reverseBits(unsigned int p_nIndex, unsigned int p_nBits)
+{
+    unsigned int i, rev;
+
+    for(i=rev=0; i < p_nBits; i++)
+    {
+	rev = (rev << 1) | (p_nIndex & 1);
+	p_nIndex >>= 1;
+    }
+
+    return rev;
+}