FFmpeg
adx.c
Go to the documentation of this file.
1 /*
2  * Copyright (c) 2011 Justin Ruggles
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * FFmpeg is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with FFmpeg; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 #include "libavutil/common.h"
22 #include "libavutil/mathematics.h"
23 #include "adx.h"
24 
25 void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
26 {
27  double a, b, c;
28 
29  a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
30  b = M_SQRT2 - 1.0;
31  c = (a - sqrt((a + b) * (a - b))) / b;
32 
33  coeff[0] = lrintf(c * 2.0 * (1 << bits));
34  coeff[1] = lrintf(-(c * c) * (1 << bits));
35 }
b
#define b
Definition: input.c:41
mathematics.h
sample_rate
sample_rate
Definition: ffmpeg_filter.c:156
bits
uint8_t bits
Definition: vp3data.h:141
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
ff_adx_calculate_coeffs
void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
Calculate LPC coefficients based on cutoff frequency and sample rate.
Definition: adx.c:25
a
The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a
Definition: undefined.txt:41
M_PI
#define M_PI
Definition: mathematics.h:52
lrintf
#define lrintf(x)
Definition: libm_mips.h:72
common.h
adx.h
M_SQRT2
#define M_SQRT2
Definition: mathematics.h:61
coeff
static const double coeff[2][5]
Definition: vf_owdenoise.c:78