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/*****************************************************************************/
/*
* fft.hh -- Simple RIF FFT function.
*
* Copyright (C) 2003
* Thomas Sailer (t.sailer@alumni.ethz.ch)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*/
/*****************************************************************************/
#ifndef _FFT_HH
#define _FFT_HH
/* --------------------------------------------------------------------- */
/*
* This fft routine is from ~gabriel/src/filters/fft/fft.c;
* I am unsure of the original source. The file contains no
* copyright notice or description.
* The declaration is changed to the prototype form but the
* function body is unchanged. (J. T. Buck)
*/
/*
* Replace data by its discrete Fourier transform, if isign is
* input as 1, or by its inverse discrete Fourier transform, if
* "isign" is input as -1. "data'"is a complex array of length "nn".
* "nn" MUST be an integer power of 2 (this is not checked for!?)
*/
template<typename T> static void fft_rif(complex<T> *data, unsigned int nn, int isign)
{
for (unsigned int i = 0, j = 0; i < nn; i++) {
if (j > i) {
complex<T> temp = data[j];
data[j] = data[i];
data[i] = temp;
}
unsigned int m = nn >> 1;
while (m > 0 && (int)j >= (int)m) {
j -= m;
m >>= 1;
}
j += m;
}
unsigned int mmax = 1;
T theta = -6.28318530717959 * 0.5;
if (isign < 0)
theta = -theta;
T sintheta = sin(theta);
while (nn > mmax) {
T oldsintheta = sintheta;
theta *= 0.5;
sintheta = sin(theta);
complex<T> wp(-2.0 * sintheta * sintheta, oldsintheta); /* -2.0 * sin(0.5*theta)^2 = cos(theta)-1 */
complex<T> w(1,0);
for (unsigned int m = 0; m < mmax; m++) {
for (unsigned int i = m; i < nn; i += 2*mmax) {
unsigned int j = i + mmax;
complex<T> temp = w * data[j];
data[j] = data[i] - temp;
data[i] += temp;
}
w += w * wp;
}
mmax <<= 1;
}
}
/* ---------------------------------------------------------------------- */
#endif /* _FFT_HH */
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