2 * This file is part of FFmpeg.
4 * FFmpeg 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.
9 * FFmpeg 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.
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with FFmpeg; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19 #include "libavutil/avassert.h"
20 #include "libavutil/mathematics.h"
21 #include "libavutil/attributes.h"
24 #define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
26 av_cold
void ff_kbd_window_init(float *window
, float alpha
, int n
)
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
);
33 av_assert0(n
<= FF_KBD_WINDOW_MAX
);
35 for (i
= 0; i
< n
; i
++) {
36 tmp
= i
* (n
- i
) * alpha2
;
38 for (j
= BESSEL_I0_ITER
; j
> 0; j
--)
39 bessel
= bessel
* tmp
/ (j
* j
) + 1;
41 local_window
[i
] = sum
;
45 for (i
= 0; i
< n
; i
++)
46 window
[i
] = sqrt(local_window
[i
] / sum
);
49 av_cold
void ff_kbd_window_init_fixed(int32_t *window
, float alpha
, int n
)
52 float local_window
[FF_KBD_WINDOW_MAX
];
54 ff_kbd_window_init(local_window
, alpha
, n
);
55 for (i
= 0; i
< n
; i
++)
56 window
[i
] = (int)floor(2147483647.0 * local_window
[i
] + 0.5);