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1 | /* |
2 | * IIR filter | |
3 | * Copyright (c) 2008 Konstantin Shishkov | |
4 | * | |
5 | * This file is part of FFmpeg. | |
6 | * | |
7 | * FFmpeg is free software; you can redistribute it and/or | |
8 | * modify it under the terms of the GNU Lesser General Public | |
9 | * License as published by the Free Software Foundation; either | |
10 | * version 2.1 of the License, or (at your option) any later version. | |
11 | * | |
12 | * FFmpeg is distributed in the hope that it will be useful, | |
13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | * Lesser General Public License for more details. | |
16 | * | |
17 | * You should have received a copy of the GNU Lesser General Public | |
18 | * License along with FFmpeg; if not, write to the Free Software | |
19 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
20 | */ | |
21 | ||
22 | /** | |
23 | * @file iirfilter.c | |
24 | * different IIR filters implementation | |
25 | */ | |
26 | ||
27 | #include "iirfilter.h" | |
28 | #include <complex.h> | |
29 | #include <math.h> | |
30 | ||
31 | /** | |
32 | * IIR filter global parameters | |
33 | */ | |
34 | typedef struct FFIIRFilterCoeffs{ | |
35 | int order; | |
36 | float gain; | |
37 | int *cx; | |
38 | float *cy; | |
39 | }FFIIRFilterCoeffs; | |
40 | ||
41 | /** | |
42 | * IIR filter state | |
43 | */ | |
44 | typedef struct FFIIRFilterState{ | |
45 | float x[1]; | |
46 | }FFIIRFilterState; | |
47 | ||
48 | /// maximum supported filter order | |
49 | #define MAXORDER 30 | |
50 | ||
51 | struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, | |
52 | enum IIRFilterMode filt_mode, | |
53 | int order, float cutoff_ratio, | |
54 | float stopband, float ripple) | |
55 | { | |
56 | int i, j, size; | |
57 | FFIIRFilterCoeffs *c; | |
58 | double wa; | |
59 | complex p[MAXORDER + 1]; | |
60 | ||
61 | if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) | |
62 | return NULL; | |
63 | if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) | |
64 | return NULL; | |
65 | ||
66 | c = av_malloc(sizeof(FFIIRFilterCoeffs)); | |
67 | c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); | |
68 | c->cy = av_malloc(sizeof(c->cy[0]) * order); | |
69 | c->order = order; | |
70 | ||
71 | wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); | |
72 | ||
73 | c->cx[0] = 1; | |
74 | for(i = 1; i < (order >> 1) + 1; i++) | |
75 | c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; | |
76 | ||
77 | p[0] = 1.0; | |
78 | for(i = 1; i <= order; i++) | |
79 | p[i] = 0.0; | |
80 | for(i = 0; i < order; i++){ | |
81 | complex zp; | |
82 | double th = (i + (order >> 1) + 0.5) * M_PI / order; | |
83 | zp = cexp(I*th) * wa; | |
84 | zp = (zp + 2.0) / (zp - 2.0); | |
85 | ||
86 | for(j = order; j >= 1; j--) | |
87 | p[j] = zp*p[j] + p[j - 1]; | |
88 | p[0] *= zp; | |
89 | } | |
90 | c->gain = creal(p[order]); | |
91 | for(i = 0; i < order; i++){ | |
92 | c->gain += creal(p[i]); | |
93 | c->cy[i] = creal(-p[i] / p[order]); | |
94 | } | |
95 | c->gain /= 1 << order; | |
96 | ||
97 | return c; | |
98 | } | |
99 | ||
100 | struct FFIIRFilterState* ff_iir_filter_init_state(int order) | |
101 | { | |
102 | FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); | |
103 | return s; | |
104 | } | |
105 | ||
106 | #define FILTER(i0, i1, i2, i3) \ | |
107 | in = *src * c->gain \ | |
108 | + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ | |
109 | + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ | |
110 | res = (s->x[i0] + in )*1 \ | |
111 | + (s->x[i1] + s->x[i3])*4 \ | |
112 | + s->x[i2] *6; \ | |
113 | *dst = av_clip_int16(lrintf(res)); \ | |
114 | s->x[i0] = in; \ | |
115 | src += sstep; \ | |
116 | dst += dstep; \ | |
117 | ||
118 | void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) | |
119 | { | |
120 | int i; | |
121 | ||
122 | if(c->order == 4){ | |
123 | for(i = 0; i < size; i += 4){ | |
124 | float in, res; | |
125 | ||
126 | FILTER(0, 1, 2, 3); | |
127 | FILTER(1, 2, 3, 0); | |
128 | FILTER(2, 3, 0, 1); | |
129 | FILTER(3, 0, 1, 2); | |
130 | } | |
131 | }else{ | |
132 | for(i = 0; i < size; i++){ | |
133 | int j; | |
134 | float in, res; | |
135 | in = *src * c->gain; | |
136 | for(j = 0; j < c->order; j++) | |
137 | in += c->cy[j] * s->x[j]; | |
138 | res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; | |
139 | for(j = 1; j < c->order >> 1; j++) | |
140 | res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; | |
141 | for(j = 0; j < c->order - 1; j++) | |
142 | s->x[j] = s->x[j + 1]; | |
143 | *dst = av_clip_int16(lrintf(res)); | |
144 | s->x[c->order - 1] = in; | |
145 | src += sstep; | |
146 | dst += sstep; | |
147 | } | |
148 | } | |
149 | } | |
150 | ||
151 | void ff_iir_filter_free_state(struct FFIIRFilterState *state) | |
152 | { | |
153 | av_free(state); | |
154 | } | |
155 | ||
156 | void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) | |
157 | { | |
158 | if(coeffs){ | |
159 | av_free(coeffs->cx); | |
160 | av_free(coeffs->cy); | |
161 | } | |
162 | av_free(coeffs); | |
163 | } | |
164 |