// FHT - Fast Hartley Transform Class
//
// 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, write to the Free Software
// Foundation, 51 Franklin Steet, Fifth Floor, Boston, MA 02110-1301, USA
//
// $Id$

#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