/****************************************************************************************
 * Copyright (c) 2004 Melchior FRANZ <mfranz@kde.org>                                   *
 *                                                                                      *
 * 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, see <http://www.gnu.org/licenses/>.                           *
 ****************************************************************************************/

#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);

	/**
	 * 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. This is the fastest transform.
	 * @see FHT::power()
	 */
	void	power2(float *);

	/**
	 * Discrete Hartley transform of data sets with 8 values.
	 */
	void	transform8(float *);

	void	transform(float *);
};

#endif
