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74 lines
2.4 KiB
C
74 lines
2.4 KiB
C
/* Copyright (C) 2010-2015 The RetroArch team
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*
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* ---------------------------------------------------------------------------------------
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* The following license statement only applies to this file (filters.h).
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* ---------------------------------------------------------------------------------------
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*
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* Permission is hereby granted, free of charge,
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* to any person obtaining a copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation the rights to
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* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#ifndef _LIBRETRO_SDK_FILTERS_H
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#define _LIBRETRO_SDK_FILTERS_H
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#include <math.h>
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#include <retro_inline.h>
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static INLINE double sinc(double val)
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{
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if (fabs(val) < 0.00001)
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return 1.0;
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return sin(val) / val;
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}
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/* Modified Bessel function of first order.
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* Check Wiki for mathematical definition ... */
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static INLINE double besseli0(double x)
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{
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unsigned i;
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double sum = 0.0;
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double factorial = 1.0;
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double factorial_mult = 0.0;
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double x_pow = 1.0;
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double two_div_pow = 1.0;
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double x_sqr = x * x;
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/* Approximate. This is an infinite sum.
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* Luckily, it converges rather fast. */
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for (i = 0; i < 18; i++)
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{
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sum += x_pow * two_div_pow / (factorial * factorial);
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factorial_mult += 1.0;
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x_pow *= x_sqr;
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two_div_pow *= 0.25;
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factorial *= factorial_mult;
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}
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return sum;
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}
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static INLINE double kaiser_window_function(double index, double beta)
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{
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return besseli0(beta * sqrtf(1 - index * index));
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}
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static INLINE double lanzcos_window_function(double index)
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{
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return sinc(M_PI * index);
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}
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#endif
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