/* * 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); }