gri_iir.h

Go to the documentation of this file.

/* -*- c++ -*- */
/*
 * Copyright 2002 Free Software Foundation, Inc.
 * 
 * This file is part of GNU Radio
 * 
 * GNU Radio 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, or (at your option)
 * any later version.
 * 
 * GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#ifndef INCLUDED_GRI_IIR_H
#define INCLUDED_GRI_IIR_H

#include <vector>
#include <stdexcept>

template<class i_type, class o_type, class tap_type> 
class gri_iir {
public:
  gri_iir (const std::vector<tap_type>& fftaps,
          const std::vector<tap_type>& fbtaps) throw (std::invalid_argument)
  {
    set_taps (fftaps, fbtaps);
  }

  gri_iir () : d_latest(0) { }

  ~gri_iir () {}

  o_type filter (const i_type input);

  void filter_n (o_type output[], const i_type input[], long n);

  unsigned ntaps () const { return d_fftaps.size (); }

  void set_taps (const std::vector<tap_type> &fftaps, 
                 const std::vector<tap_type> &fbtaps) throw (std::invalid_argument)
  { 
    if (fftaps.size () != fbtaps.size ())
      throw std::invalid_argument ("gri_iir::set_taps");

    d_latest = 0;
    d_fftaps = fftaps; 
    d_fbtaps = fbtaps; 

    int n = fftaps.size ();
    d_prev_input.resize (2 * n);
    d_prev_output.resize (2 * n);

    for (int i = 0; i < 2 * n; i++){
      d_prev_input[i] = 0;
      d_prev_output[i] = 0;
    }
  }

protected:
  std::vector<tap_type> d_fftaps;
  std::vector<tap_type> d_fbtaps;
  int                   d_latest;
  std::vector<tap_type> d_prev_output;
  std::vector<i_type>   d_prev_input;
};


//
// general case.  We may want to specialize this
//
template<class i_type, class o_type, class tap_type> 
o_type
gri_iir<i_type, o_type, tap_type>::filter (const i_type input)
{
  tap_type      acc;
  unsigned      i = 0;
  unsigned      n = ntaps ();

  if (n == 0)
    return (o_type) 0;

  int latest = d_latest;
  
  acc = d_fftaps[0] * input;
  for (i = 1; i < n; i ++)
    acc += (d_fftaps[i] * d_prev_input[latest + i]
            + d_fbtaps[i] * d_prev_output[latest + i]);

  // store the values twice to avoid having to handle wrap-around in the loop
  d_prev_output[latest] = acc;
  d_prev_output[latest+n] = acc;
  d_prev_input[latest] = input;
  d_prev_input[latest+n] = input;

  latest--;
  if (latest < 0)
    latest += n;

  d_latest = latest;
  return (o_type) acc;
}


template<class i_type, class o_type, class tap_type> 
void 
gri_iir<i_type, o_type, tap_type>::filter_n (o_type output[],
                                             const i_type input[],
                                             long n)
{
  for (int i = 0; i < n; i++)
    output[i] = filter (input[i]);
}

#endif /* INCLUDED_GRI_IIR_H */

---