/*
  * 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);

 }