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[libav.git] / libavcodec / iirfilter.c
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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/**
ba87f080 23 * @file
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24 * different IIR filters implementation
25 */
26
27#include "iirfilter.h"
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28#include <math.h>
29
30/**
31 * IIR filter global parameters
32 */
33typedef struct FFIIRFilterCoeffs{
34 int order;
35 float gain;
36 int *cx;
37 float *cy;
38}FFIIRFilterCoeffs;
39
40/**
41 * IIR filter state
42 */
43typedef struct FFIIRFilterState{
44 float x[1];
45}FFIIRFilterState;
46
47/// maximum supported filter order
48#define MAXORDER 30
49
c8ec2f1c 50av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
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51 enum IIRFilterMode filt_mode,
52 int order, float cutoff_ratio,
53 float stopband, float ripple)
54{
47f49f98 55 int i, j;
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56 FFIIRFilterCoeffs *c;
57 double wa;
e187d87d 58 double p[MAXORDER + 1][2];
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59
60 if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
61 return NULL;
62 if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
63 return NULL;
64
65 c = av_malloc(sizeof(FFIIRFilterCoeffs));
66 c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
67 c->cy = av_malloc(sizeof(c->cy[0]) * order);
68 c->order = order;
69
70 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
71
72 c->cx[0] = 1;
73 for(i = 1; i < (order >> 1) + 1; i++)
74 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
75
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76 p[0][0] = 1.0;
77 p[0][1] = 0.0;
a169f498 78 for(i = 1; i <= order; i++)
e187d87d 79 p[i][0] = p[i][1] = 0.0;
a169f498 80 for(i = 0; i < order; i++){
e187d87d 81 double zp[2];
a169f498 82 double th = (i + (order >> 1) + 0.5) * M_PI / order;
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83 double a_re, a_im, c_re, c_im;
84 zp[0] = cos(th) * wa;
85 zp[1] = sin(th) * wa;
86 a_re = zp[0] + 2.0;
87 c_re = zp[0] - 2.0;
88 a_im =
89 c_im = zp[1];
90 zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
91 zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
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92
93 for(j = order; j >= 1; j--)
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94 {
95 a_re = p[j][0];
96 a_im = p[j][1];
97 p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
98 p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
99 }
100 a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
101 p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
102 p[0][0] = a_re;
a169f498 103 }
e187d87d 104 c->gain = p[order][0];
a169f498 105 for(i = 0; i < order; i++){
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106 c->gain += p[i][0];
107 c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
108 (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
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109 }
110 c->gain /= 1 << order;
111
112 return c;
113}
114
c8ec2f1c 115av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
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116{
117 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
118 return s;
119}
120
121#define FILTER(i0, i1, i2, i3) \
122 in = *src * c->gain \
123 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
124 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
125 res = (s->x[i0] + in )*1 \
126 + (s->x[i1] + s->x[i3])*4 \
127 + s->x[i2] *6; \
128 *dst = av_clip_int16(lrintf(res)); \
129 s->x[i0] = in; \
130 src += sstep; \
131 dst += dstep; \
132
133void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
134{
135 int i;
136
137 if(c->order == 4){
138 for(i = 0; i < size; i += 4){
139 float in, res;
140
141 FILTER(0, 1, 2, 3);
142 FILTER(1, 2, 3, 0);
143 FILTER(2, 3, 0, 1);
144 FILTER(3, 0, 1, 2);
145 }
146 }else{
147 for(i = 0; i < size; i++){
148 int j;
149 float in, res;
150 in = *src * c->gain;
151 for(j = 0; j < c->order; j++)
152 in += c->cy[j] * s->x[j];
153 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
154 for(j = 1; j < c->order >> 1; j++)
155 res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
156 for(j = 0; j < c->order - 1; j++)
157 s->x[j] = s->x[j + 1];
158 *dst = av_clip_int16(lrintf(res));
159 s->x[c->order - 1] = in;
160 src += sstep;
c3897d76 161 dst += dstep;
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162 }
163 }
164}
165
c8ec2f1c 166av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
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167{
168 av_free(state);
169}
170
c8ec2f1c 171av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
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172{
173 if(coeffs){
174 av_free(coeffs->cx);
175 av_free(coeffs->cy);
176 }
177 av_free(coeffs);
178}
179
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180#ifdef TEST
181#define FILT_ORDER 4
182#define SIZE 1024
183int main(void)
184{
185 struct FFIIRFilterCoeffs *fcoeffs = NULL;
186 struct FFIIRFilterState *fstate = NULL;
187 float cutoff_coeff = 0.4;
188 int16_t x[SIZE], y[SIZE];
189 int i;
190 FILE* fd;
191
192 fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
193 FF_FILTER_MODE_LOWPASS, FILT_ORDER,
194 cutoff_coeff, 0.0, 0.0);
195 fstate = ff_iir_filter_init_state(FILT_ORDER);
196
197 for (i = 0; i < SIZE; i++) {
198 x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
199 }
200
201 ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
202
203 fd = fopen("in.bin", "w");
204 fwrite(x, sizeof(x[0]), SIZE, fd);
205 fclose(fd);
206
207 fd = fopen("out.bin", "w");
208 fwrite(y, sizeof(y[0]), SIZE, fd);
209 fclose(fd);
210
211 ff_iir_filter_free_coeffs(fcoeffs);
212 ff_iir_filter_free_state(fstate);
213 return 0;
214}
215#endif /* TEST */