diff options
Diffstat (limited to 'libavcodec/kbdwin.c')
-rw-r--r-- | libavcodec/kbdwin.c | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/libavcodec/kbdwin.c b/libavcodec/kbdwin.c new file mode 100644 index 0000000000..c2c1c59040 --- /dev/null +++ b/libavcodec/kbdwin.c @@ -0,0 +1,48 @@ +/* + * This file is part of Libav. + * + * Libav 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. + * + * Libav 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 Libav; 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); +} + |