Libav 0.7.1
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00001 /* 00002 * This file is part of Libav. 00003 * 00004 * Libav is free software; you can redistribute it and/or 00005 * modify it under the terms of the GNU Lesser General Public 00006 * License as published by the Free Software Foundation; either 00007 * version 2.1 of the License, or (at your option) any later version. 00008 * 00009 * Libav is distributed in the hope that it will be useful, 00010 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00011 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00012 * Lesser General Public License for more details. 00013 * 00014 * You should have received a copy of the GNU Lesser General Public 00015 * License along with Libav; if not, write to the Free Software 00016 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 00017 */ 00018 00019 #include <assert.h> 00020 #include <libavutil/mathematics.h> 00021 #include "libavutil/attributes.h" 00022 #include "kbdwin.h" 00023 00024 #define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation 00025 00026 av_cold void ff_kbd_window_init(float *window, float alpha, int n) 00027 { 00028 int i, j; 00029 double sum = 0.0, bessel, tmp; 00030 double local_window[FF_KBD_WINDOW_MAX]; 00031 double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n); 00032 00033 assert(n <= FF_KBD_WINDOW_MAX); 00034 00035 for (i = 0; i < n; i++) { 00036 tmp = i * (n - i) * alpha2; 00037 bessel = 1.0; 00038 for (j = BESSEL_I0_ITER; j > 0; j--) 00039 bessel = bessel * tmp / (j * j) + 1; 00040 sum += bessel; 00041 local_window[i] = sum; 00042 } 00043 00044 sum++; 00045 for (i = 0; i < n; i++) 00046 window[i] = sqrt(local_window[i] / sum); 00047 } 00048