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/* Copyright (C) 2010-2020 The RetroArch team
*
* ---------------------------------------------------------------------------------------
* The following license statement only applies to this file (filters.h).
* ---------------------------------------------------------------------------------------
*
* Permission is hereby granted, free of charge,
* to any person obtaining a copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#ifndef _LIBRETRO_SDK_FILTERS_H
#define _LIBRETRO_SDK_FILTERS_H
/* for MSVC; should be benign under any circumstances */
#define _USE_MATH_DEFINES
#include <stdlib.h>
#include <math.h>
#include <retro_inline.h>
#include <retro_math.h>
/**
* sinc:
*
* Pure function.
**/
static INLINE double sinc(double val)
{
if (fabs(val) < 0.00001)
return 1.0;
return sin(val) / val;
}
/**
* paeth:
*
* Pure function.
* Paeth prediction filter.
**/
static INLINE int paeth(int a, int b, int c)
{
int p = a + b - c;
int pa = abs(p - a);
int pb = abs(p - b);
int pc = abs(p - c);
if (pa <= pb && pa <= pc)
return a;
else if (pb <= pc)
return b;
return c;
}
/**
* besseli0:
*
* Pure function.
*
* Modified Bessel function of first order.
* Check Wiki for mathematical definition ...
**/
static INLINE double besseli0(double x)
{
int i;
double sum = 0.0;
double factorial = 1.0;
double factorial_mult = 0.0;
double x_pow = 1.0;
double two_div_pow = 1.0;
double x_sqr = x * x;
/* Approximate. This is an infinite sum.
* Luckily, it converges rather fast. */
for (i = 0; i < 18; i++)
{
sum += x_pow * two_div_pow / (factorial * factorial);
factorial_mult += 1.0;
x_pow *= x_sqr;
two_div_pow *= 0.25;
factorial *= factorial_mult;
}
return sum;
}
static INLINE double kaiser_window_function(double index, double beta)
{
return besseli0(beta * sqrtf(1 - index * index));
}
#endif
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