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/*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <assert.h>
#include <libavutil/mathematics.h>
#include "libavutil/attributes.h"
#include "kbdwin.h"
#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
av_cold void ff_kbd_window_init(float *window, float alpha, int n)
{
int i, j;
double sum = 0.0, bessel, tmp;
double local_window[FF_KBD_WINDOW_MAX];
double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
assert(n <= FF_KBD_WINDOW_MAX);
for (i = 0; i < n; i++) {
tmp = i * (n - i) * alpha2;
bessel = 1.0;
for (j = BESSEL_I0_ITER; j > 0; j--)
bessel = bessel * tmp / (j * j) + 1;
sum += bessel;
local_window[i] = sum;
}
sum++;
for (i = 0; i < n; i++)
window[i] = sqrt(local_window[i] / sum);
}
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