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// FHT - Fast Hartley Transform Class
//
// Copyright (C) 2004 Melchior FRANZ - [email protected]
//
// 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, 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA
//
// $Id: fht.h,v 1.3 2004/06/05 20:20:36 mfranz Exp $
#ifndef FHT_H
#define FHT_H
/**
* Implementation of the Hartley Transform after Bracewell's discrete
* algorithm. The algorithm is subject to US patent No. 4,646,256 (1987)
* but was put into public domain by the Board of Trustees of Stanford
* University in 1994 and is now freely available[1].
*
* [1] Computer in Physics, Vol. 9, No. 4, Jul/Aug 1995 pp 373-379
*/
class FHT
{
int m_exp2;
int m_num;
float *m_buf;
float *m_tab;
int *m_log;
/**
* Create a table of CAS (cosine and sine) values.
* Has only to be done in the constructor and saves from
* calculating the same values over and over while transforming.
*/
void makeCasTable();
/**
* Recursive in-place Hartley transform. For internal use only!
*/
void _transform(float *, int, int);
public:
/**
* Prepare transform for data sets with @f$2^n@f$ numbers, whereby @f$n@f$
* should be at least 3. Values of more than 3 need a trigonometry table.
* @see makeCasTable()
*/
FHT(int);
~FHT();
inline int sizeExp() const { return m_exp2; }
inline int size() const { return m_num; }
float *copy(float *, float *);
float *clear(float *);
void scale(float *, float);
/**
* Exponentially Weighted Moving Average (EWMA) filter.
* @param d is the filtered data.
* @param s is fresh input.
* @param w is the weighting factor.
*/
void ewma(float *d, float *s, float w);
/**
* Test routine to create wobbling sine or rectangle wave.
* @param d destination vector.
* @param rect rectangle if true, sine otherwise.
*/
void pattern(float *d, bool rect);
/**
* Logarithmic audio spectrum. Maps semi-logarithmic spectrum
* to logarithmic frequency scale, interpolates missing values.
* A logarithmic index map is calculated at the first run only.
* @param p is the input array.
* @param out is the spectrum.
*/
void logSpectrum(float *out, float *p);
/**
* Semi-logarithmic audio spectrum.
*/
void semiLogSpectrum(float *);
/**
* Fourier spectrum.
*/
void spectrum(float *);
/**
* Calculates a mathematically correct FFT power spectrum.
* If further scaling is applied later, use power2 instead
* and factor the 0.5 in the final scaling factor.
* @see FHT::power2()
*/
void power(float *);
/**
* Calculates an FFT power spectrum with doubled values as a
* result. The values need to be multiplied by 0.5 to be exact.
* Note that you only get @f$2^{n-1}@f$ power values for a data set
* of @f$2^n@f$ input values.
* @see FHT::power()
*/
void power2(float *);
/**
* Discrete Hartley transform of data sets with 8 values.
*/
void transform8(float *);
void transform(float *);
};
#endif
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