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/*____________________________________________________________________________
MusicBrainz -- The Internet music metadatabase
Portions Copyright (C) 2000 Relatable
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
$Id: sigfft.cpp,v 1.6 2001/07/06 21:32:13 robert Exp $
____________________________________________________________________________*/
//------------------------------------
// fft.cpp
// The implementation of the
// Fast Fourier Transform algorithm
// modified by Sean Ward 2000
// portions (c) Reliable Software, 1996
//------------------------------------
#include "sigfft.h"
#include <string.h>
// log (1) = 0, log(2) = 1, log(3) = 2, log(4) = 2 ...
#ifdef PI
#undef PI
#endif
#define PI (2.0 * asin(1.0))
// Points must be a power of 2
FFT::FFT (int Points, long sampleRate)
: _Points (Points), _sampleRate (sampleRate)
{
_aTape = new double [_Points];
#if 0
// 1 kHz calibration wave
for (int i = 0; i < _Points; i++)
_aTape[i] = 1600 * sin (2 * PI * 1000. * i / _sampleRate);
#else
int i = 0;
for (i = 0; i < _Points; i++)
_aTape[i] = 0;
#endif
_sqrtPoints = sqrt((double)_Points);
// calculate binary log
_logPoints = 0;
Points--;
while (Points != 0)
{
Points >>= 1;
_logPoints++;
}
_aBitRev = new int [_Points];
_Bleh = new Complex[_Points];
_W = new Complex* [_logPoints+1];
// Precompute complex exponentials
int _2_l = 2;
for (int l = 1; l <= _logPoints; l++)
{
_W[l] = new Complex [_Points];
for ( int i = 0; i < _Points; i++ )
{
double re = cos (2. * PI * i / _2_l);
double im = -sin (2. * PI * i / _2_l);
_W[l][i] = Complex (re, im);
}
_2_l *= 2;
}
// set up bit reverse mapping
int rev = 0;
int halfPoints = _Points/2;
for (i = 0; i < _Points - 1; i++)
{
_aBitRev[i] = rev;
int mask = halfPoints;
// add 1 backwards
while (rev >= mask)
{
rev -= mask; // turn off this bit
mask >>= 1;
}
rev += mask;
}
_aBitRev [_Points-1] = _Points-1;
}
FFT::~FFT()
{
delete []_aTape;
delete []_aBitRev;
for (int l = 1; l <= _logPoints; l++)
{
delete []_W[l];
}
delete []_W;
delete []_Bleh;
}
//void Fft::CopyIn (SampleIter& iter)
void FFT::CopyIn(double* pBuffer, int nNumSamples)
{
if (nNumSamples > _Points)
return;
// make space for cSample samples at the end of tape
// shifting previous samples towards the beginning
memmove (_aTape, &_aTape[nNumSamples],
(_Points - nNumSamples) * sizeof(double));
// copy samples from iterator to tail end of tape
int iTail = _Points - nNumSamples;
int i = 0;
for (i = 0; i < nNumSamples; i++)
{
_aTape [i + iTail] = pBuffer[i];
}
// Initialize the FFT buffer
for (i = 0; i < _Points; i++)
PutAt (i, _aTape[i]);
}
void FFT::CopyIn2(double* pBuf, double* pBuf2, int nNumSamples)
{
if (nNumSamples > _Points)
return;
int i = 0;
// Initialize the FFT buffer
for (i = 0; i < _Points; i++)
PutAt2 (i, pBuf[i], pBuf2[i]);
}
//
// 0 1 2 3 4 5 6 7
// level 1
// step 1 0
// increm 2 W
// j = 0 <---> <---> <---> <---> 1
// level 2
// step 2
// increm 4 0
// j = 0 <-------> <-------> W 1
// j = 1 <-------> <-------> 2 W
// level 3 2
// step 4
// increm 8 0
// j = 0 <---------------> W 1
// j = 1 <---------------> 3 W 2
// j = 2 <---------------> 3 W 3
// j = 3 <---------------> 3 W
// 3
//
void FFT::Transform ()
{
// step = 2 ^ (level-1)
// increm = 2 ^ level;
int step = 1;
for (int level = 1; level <= _logPoints; level++)
{
int increm = step * 2;
for (int j = 0; j < step; j++)
{
// U = exp ( - 2 PI j / 2 ^ level )
Complex U = _W [level][j];
for (int i = j; i < _Points; i += increm)
{
// butterfly
Complex T = U;
T *= _Bleh[i+step];
_Bleh[i+step] = _Bleh[i];
_Bleh[i+step] -= T;
_Bleh[i] += T;
}
}
step *= 2;
}
}
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