1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
|
/*
* IIR filter
* Copyright (c) 2008 Konstantin Shishkov
*
* This file is part of FFmpeg.
*
* FFmpeg 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.
*
* FFmpeg 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 FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file libavcodec/iirfilter.c
* different IIR filters implementation
*/
#include "iirfilter.h"
#include <math.h>
/**
* IIR filter global parameters
*/
typedef struct FFIIRFilterCoeffs{
int order;
float gain;
int *cx;
float *cy;
}FFIIRFilterCoeffs;
/**
* IIR filter state
*/
typedef struct FFIIRFilterState{
float x[1];
}FFIIRFilterState;
/// maximum supported filter order
#define MAXORDER 30
struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
enum IIRFilterMode filt_mode,
int order, float cutoff_ratio,
float stopband, float ripple)
{
int i, j, size;
FFIIRFilterCoeffs *c;
double wa;
double p[MAXORDER + 1][2];
if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
return NULL;
if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
return NULL;
c = av_malloc(sizeof(FFIIRFilterCoeffs));
c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
c->cy = av_malloc(sizeof(c->cy[0]) * order);
c->order = order;
wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
c->cx[0] = 1;
for(i = 1; i < (order >> 1) + 1; i++)
c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
p[0][0] = 1.0;
p[0][1] = 0.0;
for(i = 1; i <= order; i++)
p[i][0] = p[i][1] = 0.0;
for(i = 0; i < order; i++){
double zp[2];
double th = (i + (order >> 1) + 0.5) * M_PI / order;
double a_re, a_im, c_re, c_im;
zp[0] = cos(th) * wa;
zp[1] = sin(th) * wa;
a_re = zp[0] + 2.0;
c_re = zp[0] - 2.0;
a_im =
c_im = zp[1];
zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
for(j = order; j >= 1; j--)
{
a_re = p[j][0];
a_im = p[j][1];
p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
}
a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
p[0][0] = a_re;
}
c->gain = p[order][0];
for(i = 0; i < order; i++){
c->gain += p[i][0];
c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
(p[order][0] * p[order][0] + p[order][1] * p[order][1]);
}
c->gain /= 1 << order;
return c;
}
struct FFIIRFilterState* ff_iir_filter_init_state(int order)
{
FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
return s;
}
#define FILTER(i0, i1, i2, i3) \
in = *src * c->gain \
+ c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
+ c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
res = (s->x[i0] + in )*1 \
+ (s->x[i1] + s->x[i3])*4 \
+ s->x[i2] *6; \
*dst = av_clip_int16(lrintf(res)); \
s->x[i0] = in; \
src += sstep; \
dst += dstep; \
void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
{
int i;
if(c->order == 4){
for(i = 0; i < size; i += 4){
float in, res;
FILTER(0, 1, 2, 3);
FILTER(1, 2, 3, 0);
FILTER(2, 3, 0, 1);
FILTER(3, 0, 1, 2);
}
}else{
for(i = 0; i < size; i++){
int j;
float in, res;
in = *src * c->gain;
for(j = 0; j < c->order; j++)
in += c->cy[j] * s->x[j];
res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
for(j = 1; j < c->order >> 1; j++)
res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
for(j = 0; j < c->order - 1; j++)
s->x[j] = s->x[j + 1];
*dst = av_clip_int16(lrintf(res));
s->x[c->order - 1] = in;
src += sstep;
dst += sstep;
}
}
}
void ff_iir_filter_free_state(struct FFIIRFilterState *state)
{
av_free(state);
}
void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
{
if(coeffs){
av_free(coeffs->cx);
av_free(coeffs->cy);
}
av_free(coeffs);
}
|
