1/*
2 * This file is part of Libav.
3 *
4 * Libav is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2.1 of the License, or (at your option) any later version.
8 *
9 * Libav is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12 * Lesser General Public License for more details.
13 *
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with Libav; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17 */
18
19#include <assert.h>
20#include <libavutil/mathematics.h>
21#include "libavutil/attributes.h"
22#include "kbdwin.h"
23
24#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
25
26av_cold void ff_kbd_window_init(float *window, float alpha, int n)
27{
28   int i, j;
29   double sum = 0.0, bessel, tmp;
30   double local_window[FF_KBD_WINDOW_MAX];
31   double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
32
33   assert(n <= FF_KBD_WINDOW_MAX);
34
35   for (i = 0; i < n; i++) {
36       tmp = i * (n - i) * alpha2;
37       bessel = 1.0;
38       for (j = BESSEL_I0_ITER; j > 0; j--)
39           bessel = bessel * tmp / (j * j) + 1;
40       sum += bessel;
41       local_window[i] = sum;
42   }
43
44   sum++;
45   for (i = 0; i < n; i++)
46       window[i] = sqrt(local_window[i] / sum);
47}
48
49