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