/* -*- c++ -*- */
/*
 * Copyright 2004,2012 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */

#ifndef INCLUDED_IIR_FILTER_FFD_H
#define INCLUDED_IIR_FILTER_FFD_H

#include <gnuradio/filter/api.h>
#include <gnuradio/sync_block.h>

namespace gr {
namespace filter {

/*!
 * \brief  IIR filter with float input, float output and double taps
 * \ingroup filter_blk
 *
 * \details
 * This filter uses the Direct Form I implementation, where
 * \p fftaps contains the feed-forward taps, and \p fbtaps the feedback ones.
 *
 * \p oldstyle: The old style of the IIR filter uses feedback
 * taps that are negative of what most definitions use (scipy
 * and Matlab among them). This parameter keeps using the old
 * GNU Radio style and is set to TRUE by default. When taps
 * generated from scipy, Matlab, or gr_filter_design, use the
 * new style by setting this to FALSE.
 *
 * The input and output satisfy a difference equation of the form
 \f[
   y[n] - \sum_{k=1}^{M} a_k y[n-k] = \sum_{k=0}^{N} b_k x[n-k]
 \f]

 \xmlonly
 y[n] - \sum_{k=1}^{M} a_k y[n-k] = \sum_{k=0}^{N} b_k x[n-k]
 \endxmlonly

 * with the corresponding rational system function
 \f[
 H(z) = \frac{\sum_{k=0}^{M} b_k z^{-k}}{1 - \sum_{k=1}^{N} a_k z^{-k}}
 \f]

 \xmlonly
 H(z) = \ frac{\sum_{k=0}^{M} b_k z^{-k}}{1 - \sum_{k=1}^{N} a_k z^{-k}}
 \endxmlonly

 */
class FILTER_API iir_filter_ffd : virtual public sync_block
{
public:
    // gr::filter::iir_filter_ffd::sptr
    typedef std::shared_ptr<iir_filter_ffd> sptr;

    static sptr make(const std::vector<double>& fftaps,
                     const std::vector<double>& fbtaps,
                     bool oldstyle = true);

    virtual void set_taps(const std::vector<double>& fftaps,
                          const std::vector<double>& fbtaps) = 0;
};

} /* namespace filter */
} /* namespace gr */

#endif /* INCLUDED_IIR_FILTER_FFD_H */
