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sinc.h

// Copyright 2004 David Hilvert <dhilvert@auricle.dyndns.org>,
//                              <dhilvert@ugcs.caltech.edu>

/*  This file is part of the Anti-Lamenessing Engine.

    The Anti-Lamenessing Engine 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.

    The Anti-Lamenessing Engine 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 the Anti-Lamenessing Engine; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#ifndef __sinc_h__
#define __sinc_h__

/*
 * A filtering class for the sinc function.
 *
 * Notes on Lanczos and Sinc by Dave Martindale et alia are available here:
 *
 *    http://www.binbooks.com/books/photo/i/l/57186AF8DE
 *    http://www.binbooks.com/books/photo/i/l/57186AE7E6&orig=1
 */

class sinc : public filter {
public:

      /*
       * Sinc filter.
       *
       * Width is infinite.
       */
      static double _sinc(ale_pos p) {
            if (fabs(p) < 0.001)
                  return 1;
            return sin(M_PI * p) / (M_PI * p);
      }

      static double _sinc(point p) {
            return _sinc(p[0]) * _sinc(p[1]);
      }

      virtual int equals(const filter *f) const {
            if (typeid(*f) == typeid(*this))
                  return 1;
            return 0;
      }

      /*
       * Size of filter support, in number of half-cycles to each side of the
       * filter center.
       */
      virtual ale_real support() const {
            double zero = 0;
            double infinity = 1 / zero;
            assert (!isnan(infinity));
            assert (1 < infinity);
            return (ale_real) infinity;
      }

      /*
       * Response of filter at point p
       */
      virtual ale_real response(point p) const {
            return _sinc(p);
      }
};
#endif

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