sinc.h

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/*
        dsp/sinc.h
        
        Copyright 2003-4 Tim Goetze <tim@quitte.de>
        
        http://quitte.de/dsp/
 
        computes the sinc function: sin (x * pi) / (x * pi).
 
*/
/*
        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, Inc., 59 Temple Place - Suite 330, Boston, MA
        02111-1307, USA or point your web browser to http://www.gnu.org.
*/
 
#ifndef _SINC_H_
#define _SINC_H_
 
#include "Sine.h"
 
namespace DSP {
        
/* sample sinc() with step size omega into s[], centered around s + n / 2 */
 
inline void
sinc (double omega, sample_t * s, int n)
{
        /* initial phase */
        double phi = (n / 2) * -omega;
 
        Sine sine (omega, phi);
        
        for (int i = 0; i < n; ++i, phi += omega)
        {
                double sin_phi = sine.get();
 
                if (fabs (phi) < 0.000000001)
                        s[i] = 1.;
                else
                        s[i] = sin_phi / phi;
        }
}
 
}; /* namespace DSP */
 
#endif /* _SINC_H_ */