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NFFT
3.3.2
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00001 /* 00002 * Copyright (c) 2002, 2016 Jens Keiner, Stefan Kunis, Daniel Potts 00003 * 00004 * This program is free software; you can redistribute it and/or modify it under 00005 * the terms of the GNU General Public License as published by the Free Software 00006 * Foundation; either version 2 of the License, or (at your option) any later 00007 * version. 00008 * 00009 * This program is distributed in the hope that it will be useful, but WITHOUT 00010 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 00011 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more 00012 * details. 00013 * 00014 * You should have received a copy of the GNU General Public License along with 00015 * this program; if not, write to the Free Software Foundation, Inc., 51 00016 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. 00017 */ 00018 00019 #include "infft.h" 00020 00021 R Y(sinc)(const R x) 00022 { 00023 /* Based on sinc function from Boost C++ library. */ 00024 const R b = EPSILON; 00025 const R bs = SQRT(b); 00026 const R bs2 = SQRT(bs); 00027 00028 if (FABS(x) >= bs2) 00029 return SIN(x)/x; 00030 else 00031 { 00032 R r = K(1.0); 00033 00034 if (FABS(x) >= b) 00035 { 00036 const R x2 = x * x; 00037 r -= x2 / K(6.0); 00038 00039 if (FABS(x) >= bs) 00040 r += (x2 * x2) / K(120.0); 00041 } 00042 00043 return r; 00044 } 00045 }