sinc.c
/*
* Copyright (c) 2002, 2017 Jens Keiner, Stefan Kunis, Daniel Potts
*
* 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., 51
* Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include "infft.h"
R Y(sinc)(const R x)
{
/* Based on sinc function from Boost C++ library. */
const R b = NFFT_EPSILON;
const R bs = SQRT(b);
const R bs2 = SQRT(bs);
if (FABS(x) >= bs2)
return SIN(x)/x;
else
{
R r = K(1.0);
if (FABS(x) >= b)
{
const R x2 = x * x;
r -= x2 / K(6.0);
if (FABS(x) >= bs)
r += (x2 * x2) / K(120.0);
}
return r;
}
}