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48 lines
1.5 KiB
C
48 lines
1.5 KiB
C
/*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <assert.h>
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#include <libavutil/mathematics.h>
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#include "libavutil/attributes.h"
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#include "kbdwin.h"
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#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
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av_cold void ff_kbd_window_init(float *window, float alpha, int n)
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{
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int i, j;
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double sum = 0.0, bessel, tmp;
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double local_window[FF_KBD_WINDOW_MAX];
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double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
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assert(n <= FF_KBD_WINDOW_MAX);
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for (i = 0; i < n; i++) {
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tmp = i * (n - i) * alpha2;
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bessel = 1.0;
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for (j = BESSEL_I0_ITER; j > 0; j--)
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bessel = bessel * tmp / (j * j) + 1;
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sum += bessel;
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local_window[i] = sum;
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}
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sum++;
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for (i = 0; i < n; i++)
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window[i] = sqrt(local_window[i] / sum);
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}
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