/*

  * IIR filter

  * Copyright (c) 2008 Konstantin Shishkov
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**

  * @file

  * IIR filter interface

  */
 

 #ifndef AVCODEC_IIRFILTER_H
 #define AVCODEC_IIRFILTER_H

 
 #include "avcodec.h"
 

 struct FFIIRFilterCoeffs;
 struct FFIIRFilterState;
 
 enum IIRFilterType{
     FF_FILTER_TYPE_BESSEL,

     FF_FILTER_TYPE_BIQUAD,

     FF_FILTER_TYPE_BUTTERWORTH,
     FF_FILTER_TYPE_CHEBYSHEV,
     FF_FILTER_TYPE_ELLIPTIC,
 };
 
 enum IIRFilterMode{
     FF_FILTER_MODE_LOWPASS,
     FF_FILTER_MODE_HIGHPASS,
     FF_FILTER_MODE_BANDPASS,
     FF_FILTER_MODE_BANDSTOP,
 };

 
 /**
  * Initialize filter coefficients.
  *

  * @param avc          a pointer to an arbitrary struct of which the first
  *                     field is a pointer to an AVClass struct

  * @param filt_type    filter type (e.g. Butterworth)
  * @param filt_mode    filter mode (e.g. lowpass)

  * @param order        filter order
  * @param cutoff_ratio cutoff to input frequency ratio

  * @param stopband     stopband to input frequency ratio (used by bandpass and bandstop filter modes)
  * @param ripple       ripple factor (used only in Chebyshev filters)

  *
  * @return pointer to filter coefficients structure or NULL if filter cannot be created
  */

 struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
                                                 enum IIRFilterType filt_type,

                                                 enum IIRFilterMode filt_mode,
                                                 int order, float cutoff_ratio,
                                                 float stopband, float ripple);

 
 /**
  * Create new filter state.
  *
  * @param order filter order
  *
  * @return pointer to new filter state or NULL if state creation fails
  */

 struct FFIIRFilterState* ff_iir_filter_init_state(int order);

 
 /**
  * Free filter coefficients.
  *

  * @param coeffs pointer allocated with ff_iir_filter_init_coeffs()

  */

 void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs);

 
 /**
  * Free filter state.
  *

  * @param state pointer allocated with ff_iir_filter_init_state()

  */

 void ff_iir_filter_free_state(struct FFIIRFilterState *state);

 
 /**

  * Perform IIR filtering on signed 16-bit input samples.

  *
  * @param coeffs pointer to filter coefficients
  * @param state  pointer to filter state
  * @param size   input length
  * @param src    source samples
  * @param sstep  source stride
  * @param dst    filtered samples (destination may be the same as input)
  * @param dstep  destination stride
  */

 void ff_iir_filter(const struct FFIIRFilterCoeffs *coeffs, struct FFIIRFilterState *state,
                    int size, const int16_t *src, int sstep, int16_t *dst, int dstep);

 /**
  * Perform IIR filtering on floating-point input samples.
  *
  * @param coeffs pointer to filter coefficients
  * @param state  pointer to filter state
  * @param size   input length
  * @param src    source samples
  * @param sstep  source stride
  * @param dst    filtered samples (destination may be the same as input)
  * @param dstep  destination stride
  */
 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *coeffs,
                        struct FFIIRFilterState *state, int size,

                        const float *src, int sstep, float *dst, int dstep);

 #endif /* AVCODEC_IIRFILTER_H */