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