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120 lines
3.3 KiB
120 lines
3.3 KiB
// FHT - Fast Hartley Transform Class
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//
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// Copyright (C) 2004 Melchior FRANZ - mfranz@kde.org
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (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, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// 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, 51 Franklin Steet, Fifth Floor, Boston, MA 02110-1301, USA
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//
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// $Id: fht.h 439804 2005-07-28 23:45:59Z mueller $
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#ifndef FHT_H
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#define FHT_H
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/**
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* Implementation of the Hartley Transform after Bracewell's discrete
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* algorithm. The algorithm is subject to US patent No. 4,646,256 (1987)
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* but was put into public domain by the Board of Trustees of Stanford
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* University in 1994 and is now freely available[1].
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*
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* [1] Computer in Physics, Vol. 9, No. 4, Jul/Aug 1995 pp 373-379
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*/
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class FHT
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{
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int m_exp2;
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int m_num;
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float *m_buf;
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float *m_tab;
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int *m_log;
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/**
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* Create a table of "cas" (cosine and sine) values.
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* Has only to be done in the constructor and saves from
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* calculating the same values over and over while transforming.
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*/
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void makeCasTable();
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/**
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* Recursive in-place Hartley transform. For internal use only!
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*/
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void _transform(float *, int, int);
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public:
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/**
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* Prepare transform for data sets with @f$2^n@f$ numbers, whereby @f$n@f$
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* should be at least 3. Values of more than 3 need a trigonometry table.
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* @see makeCasTable()
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*/
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FHT(int);
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~FHT();
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inline int sizeExp() const { return m_exp2; }
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inline int size() const { return m_num; }
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float *copy(float *, float *);
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float *clear(float *);
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void scale(float *, float);
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/**
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* Exponentially Weighted Moving Average (EWMA) filter.
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* @param d is the filtered data.
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* @param s is fresh input.
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* @param w is the weighting factor.
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*/
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void ewma(float *d, float *s, float w);
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/**
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* Logarithmic audio spectrum. Maps semi-logarithmic spectrum
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* to logarithmic frequency scale, interpolates missing values.
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* A logarithmic index map is calculated at the first run only.
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* @param p is the input array.
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* @param out is the spectrum.
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*/
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void logSpectrum(float *out, float *p);
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/**
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* Semi-logarithmic audio spectrum.
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*/
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void semiLogSpectrum(float *);
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/**
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* Fourier spectrum.
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*/
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void spectrum(float *);
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/**
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* Calculates a mathematically correct FFT power spectrum.
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* If further scaling is applied later, use power2 instead
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* and factor the 0.5 in the final scaling factor.
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* @see FHT::power2()
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*/
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void power(float *);
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/**
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* Calculates an FFT power spectrum with doubled values as a
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* result. The values need to be multiplied by 0.5 to be exact.
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* Note that you only get @f$2^{n-1}@f$ power values for a data set
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* of @f$2^n@f$ input values. This is the fastest transform.
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* @see FHT::power()
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*/
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void power2(float *);
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/**
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* Discrete Hartley transform of data sets with 8 values.
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*/
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void transform8(float *);
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void transform(float *);
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};
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#endif
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