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https://github.com/VK3FNG/soundmodem.git
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88 lines
2.9 KiB
C++
88 lines
2.9 KiB
C++
/*****************************************************************************/
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/*
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* fft.hh -- Simple RIF FFT function.
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*
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* Copyright (C) 2003
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* Thomas Sailer (t.sailer@alumni.ethz.ch)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*/
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/*****************************************************************************/
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#ifndef _FFT_HH
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#define _FFT_HH
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/* --------------------------------------------------------------------- */
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/*
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* This fft routine is from ~gabriel/src/filters/fft/fft.c;
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* I am unsure of the original source. The file contains no
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* copyright notice or description.
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* The declaration is changed to the prototype form but the
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* function body is unchanged. (J. T. Buck)
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*/
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/*
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* Replace data by its discrete Fourier transform, if isign is
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* input as 1, or by its inverse discrete Fourier transform, if
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* "isign" is input as -1. "data'"is a complex array of length "nn".
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* "nn" MUST be an integer power of 2 (this is not checked for!?)
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*/
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template<typename T> static void fft_rif(complex<T> *data, unsigned int nn, int isign)
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{
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for (unsigned int i = 0, j = 0; i < nn; i++) {
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if (j > i) {
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complex<T> temp = data[j];
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data[j] = data[i];
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data[i] = temp;
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}
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unsigned int m = nn >> 1;
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while (m > 0 && (int)j >= (int)m) {
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j -= m;
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m >>= 1;
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}
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j += m;
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}
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unsigned int mmax = 1;
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T theta = -6.28318530717959 * 0.5;
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if (isign < 0)
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theta = -theta;
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T sintheta = sin(theta);
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while (nn > mmax) {
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T oldsintheta = sintheta;
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theta *= 0.5;
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sintheta = sin(theta);
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complex<T> wp(-2.0 * sintheta * sintheta, oldsintheta); /* -2.0 * sin(0.5*theta)^2 = cos(theta)-1 */
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complex<T> w(1,0);
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for (unsigned int m = 0; m < mmax; m++) {
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for (unsigned int i = m; i < nn; i += 2*mmax) {
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unsigned int j = i + mmax;
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complex<T> temp = w * data[j];
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data[j] = data[i] - temp;
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data[i] += temp;
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}
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w += w * wp;
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}
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mmax <<= 1;
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}
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}
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/* ---------------------------------------------------------------------- */
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#endif /* _FFT_HH */
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