c@225: /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
c@225: 
c@225: /*
c@225:     QM DSP Library
c@225: 
c@225:     Centre for Digital Music, Queen Mary, University of London.
c@225:     This file is based on Don Cross's public domain FFT implementation.
c@225: */
c@225: 
c@225: #include "FFT.h"
c@225: #include <cmath>
c@225: 
c@225: //////////////////////////////////////////////////////////////////////
c@225: // Construction/Destruction
c@225: //////////////////////////////////////////////////////////////////////
c@225: 
c@225: FFT::FFT()
c@225: {
c@225: 
c@225: }
c@225: 
c@225: FFT::~FFT()
c@225: {
c@225: 
c@225: }
c@225: 
c@225: void FFT::process(unsigned int p_nSamples, bool p_bInverseTransform, double *p_lpRealIn, double *p_lpImagIn, double *p_lpRealOut, double *p_lpImagOut)
c@225: {
c@225: 
c@225:     if(!p_lpRealIn || !p_lpRealOut || !p_lpImagOut) return;
c@225: 
c@225: 
c@225:     unsigned int NumBits;
c@225:     unsigned int i, j, k, n;
c@225:     unsigned int BlockSize, BlockEnd;
c@225: 
c@225:     double angle_numerator = 2.0 * M_PI;
c@225:     double tr, ti;
c@225: 
c@225:     if( !isPowerOfTwo(p_nSamples) )
c@225:     {
c@225: 	return;
c@225:     }
c@225: 
c@225:     if( p_bInverseTransform ) angle_numerator = -angle_numerator;
c@225: 
c@225:     NumBits = numberOfBitsNeeded ( p_nSamples );
c@225: 
c@225: 
c@225:     for( i=0; i < p_nSamples; i++ )
c@225:     {
c@225: 	j = reverseBits ( i, NumBits );
c@225: 	p_lpRealOut[j] = p_lpRealIn[i];
c@225: 	p_lpImagOut[j] = (p_lpImagIn == 0) ? 0.0 : p_lpImagIn[i];
c@225:     }
c@225: 
c@225: 
c@225:     BlockEnd = 1;
c@225:     for( BlockSize = 2; BlockSize <= p_nSamples; BlockSize <<= 1 )
c@225:     {
c@225: 	double delta_angle = angle_numerator / (double)BlockSize;
c@225: 	double sm2 = -sin ( -2 * delta_angle );
c@225: 	double sm1 = -sin ( -delta_angle );
c@225: 	double cm2 = cos ( -2 * delta_angle );
c@225: 	double cm1 = cos ( -delta_angle );
c@225: 	double w = 2 * cm1;
c@225: 	double ar[3], ai[3];
c@225: 
c@225: 	for( i=0; i < p_nSamples; i += BlockSize )
c@225: 	{
c@225: 
c@225: 	    ar[2] = cm2;
c@225: 	    ar[1] = cm1;
c@225: 
c@225: 	    ai[2] = sm2;
c@225: 	    ai[1] = sm1;
c@225: 
c@225: 	    for ( j=i, n=0; n < BlockEnd; j++, n++ )
c@225: 	    {
c@225: 
c@225: 		ar[0] = w*ar[1] - ar[2];
c@225: 		ar[2] = ar[1];
c@225: 		ar[1] = ar[0];
c@225: 
c@225: 		ai[0] = w*ai[1] - ai[2];
c@225: 		ai[2] = ai[1];
c@225: 		ai[1] = ai[0];
c@225: 
c@225: 		k = j + BlockEnd;
c@225: 		tr = ar[0]*p_lpRealOut[k] - ai[0]*p_lpImagOut[k];
c@225: 		ti = ar[0]*p_lpImagOut[k] + ai[0]*p_lpRealOut[k];
c@225: 
c@225: 		p_lpRealOut[k] = p_lpRealOut[j] - tr;
c@225: 		p_lpImagOut[k] = p_lpImagOut[j] - ti;
c@225: 
c@225: 		p_lpRealOut[j] += tr;
c@225: 		p_lpImagOut[j] += ti;
c@225: 
c@225: 	    }
c@225: 	}
c@225: 
c@225: 	BlockEnd = BlockSize;
c@225: 
c@225:     }
c@225: 
c@225: 
c@225:     if( p_bInverseTransform )
c@225:     {
c@225: 	double denom = (double)p_nSamples;
c@225: 
c@225: 	for ( i=0; i < p_nSamples; i++ )
c@225: 	{
c@225: 	    p_lpRealOut[i] /= denom;
c@225: 	    p_lpImagOut[i] /= denom;
c@225: 	}
c@225:     }
c@225: }
c@225: 
c@225: bool FFT::isPowerOfTwo(unsigned int p_nX)
c@225: {
c@225:     if( p_nX < 2 ) return false;
c@225: 
c@225:     if( p_nX & (p_nX-1) ) return false;
c@225: 
c@225:     return true;
c@225: }
c@225: 
c@225: unsigned int FFT::numberOfBitsNeeded(unsigned int p_nSamples)
c@225: {	
c@225:     int i;
c@225: 
c@225:     if( p_nSamples < 2 )
c@225:     {
c@225: 	return 0;
c@225:     }
c@225: 
c@225:     for ( i=0; ; i++ )
c@225:     {
c@225: 	if( p_nSamples & (1 << i) ) return i;
c@225:     }
c@225: }
c@225: 
c@225: unsigned int FFT::reverseBits(unsigned int p_nIndex, unsigned int p_nBits)
c@225: {
c@225:     unsigned int i, rev;
c@225: 
c@225:     for(i=rev=0; i < p_nBits; i++)
c@225:     {
c@225: 	rev = (rev << 1) | (p_nIndex & 1);
c@225: 	p_nIndex >>= 1;
c@225:     }
c@225: 
c@225:     return rev;
c@225: }