Add biquad high-pass and low-pass IIR filters.
[ffmpeg.git] / libavcodec / iirfilter.c
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
24  * different IIR filters implementation
25  */
26
27 #include "iirfilter.h"
28 #include <math.h>
29
30 /**
31  * IIR filter global parameters
32  */
33 typedef struct FFIIRFilterCoeffs{
34     int   order;
35     float gain;
36     int   *cx;
37     float *cy;
38 }FFIIRFilterCoeffs;
39
40 /**
41  * IIR filter state
42  */
43 typedef struct FFIIRFilterState{
44     float x[1];
45 }FFIIRFilterState;
46
47 /// maximum supported filter order
48 #define MAXORDER 30
49
50 static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
51                                    enum IIRFilterMode filt_mode,
52                                    int order, float cutoff_ratio,
53                                    float stopband)
54 {
55     int i, j;
56     double wa;
57     double p[MAXORDER + 1][2];
58
59     if (filt_mode != FF_FILTER_MODE_LOWPASS) {
60         av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
61                "low-pass filter mode\n");
62         return -1;
63     }
64     if (order & 1) {
65         av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
66                "even filter orders\n");
67         return -1;
68     }
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
76     p[0][0] = 1.0;
77     p[0][1] = 0.0;
78     for(i = 1; i <= order; i++)
79         p[i][0] = p[i][1] = 0.0;
80     for(i = 0; i < order; i++){
81         double zp[2];
82         double th = (i + (order >> 1) + 0.5) * M_PI / order;
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);
92
93         for(j = order; j >= 1; j--)
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;
103     }
104     c->gain = p[order][0];
105     for(i = 0; i < order; i++){
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]);
109     }
110     c->gain /= 1 << order;
111
112     return 0;
113 }
114
115 static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
116                               enum IIRFilterMode filt_mode, int order,
117                               float cutoff_ratio, float stopband)
118 {
119     double cos_w0, sin_w0;
120     double a0, x0, x1;
121
122     if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
123         filt_mode != FF_FILTER_MODE_LOWPASS) {
124         av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
125                "high-pass and low-pass filter modes\n");
126         return -1;
127     }
128     if (order != 2) {
129         av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
130         return -1;
131     }
132
133     cos_w0 = cos(M_PI * cutoff_ratio);
134     sin_w0 = sin(M_PI * cutoff_ratio);
135
136     a0 = 1.0 + (sin_w0 / 2.0);
137
138     if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
139         c->gain  =  ((1.0 + cos_w0) / 2.0)  / a0;
140         x0       = (-(1.0 + cos_w0))        / a0;
141         x1       =  ((1.0 + cos_w0) / 2.0)  / a0;
142     } else { // FF_FILTER_MODE_LOWPASS
143         c->gain  =  ((1.0 - cos_w0) / 2.0)  / a0;
144         x0       =   (1.0 - cos_w0)         / a0;
145         x1       =  ((1.0 - cos_w0) / 2.0)  / a0;
146     }
147     c->cy[0] =  (2.0 *  cos_w0)        / a0;
148     c->cy[1] = (-1.0 + (sin_w0 / 2.0)) / a0;
149
150     // divide by gain to make the x coeffs integers.
151     // during filtering, the delay state will include the gain multiplication
152     c->cx[0] = lrintf(x0 / c->gain);
153     c->cx[1] = lrintf(x1 / c->gain);
154     c->cy[0] /= c->gain;
155     c->cy[1] /= c->gain;
156
157     return 0;
158 }
159
160 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
161                                                 enum IIRFilterType filt_type,
162                                                 enum IIRFilterMode filt_mode,
163                                                 int order, float cutoff_ratio,
164                                                 float stopband, float ripple)
165 {
166     FFIIRFilterCoeffs *c;
167
168     if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
169         return NULL;
170
171     FF_ALLOCZ_OR_GOTO(avc, c,     sizeof(FFIIRFilterCoeffs),
172                       init_fail);
173     FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
174                       init_fail);
175     FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
176                       init_fail);
177     c->order = order;
178
179     if (filt_type == FF_FILTER_TYPE_BUTTERWORTH) {
180         if (butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
181             stopband)) {
182             goto init_fail;
183         }
184     } else if (filt_type == FF_FILTER_TYPE_BIQUAD) {
185         if (biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
186             stopband)) {
187             goto init_fail;
188         }
189     } else {
190         av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
191         goto init_fail;
192     }
193
194     return c;
195
196 init_fail:
197     ff_iir_filter_free_coeffs(c);
198     return NULL;
199 }
200
201 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
202 {
203     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
204     return s;
205 }
206
207 #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
208
209 #define CONV_FLT(dest, source) dest = source;
210
211 #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt)         \
212     in = *src0 * c->gain                            \
213          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]    \
214          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3];   \
215     res =  (s->x[i0] + in      )*1                  \
216          + (s->x[i1] + s->x[i3])*4                  \
217          +  s->x[i2]            *6;                 \
218     CONV_##fmt(*dst0, res)                          \
219     s->x[i0] = in;                                  \
220     src0 += sstep;                                  \
221     dst0 += dstep;
222
223 #define FILTER_BW_O4(type, fmt) {           \
224     int i;                                  \
225     const type *src0 = src;                 \
226     type       *dst0 = dst;                 \
227     for (i = 0; i < size; i += 4) {         \
228         float in, res;                      \
229         FILTER_BW_O4_1(0, 1, 2, 3, fmt);    \
230         FILTER_BW_O4_1(1, 2, 3, 0, fmt);    \
231         FILTER_BW_O4_1(2, 3, 0, 1, fmt);    \
232         FILTER_BW_O4_1(3, 0, 1, 2, fmt);    \
233     }                                       \
234 }
235
236 #define FILTER_DIRECT_FORM_II(type, fmt) {                                  \
237     int i;                                                                  \
238     const type *src0 = src;                                                 \
239     type       *dst0 = dst;                                                 \
240     for (i = 0; i < size; i++) {                                            \
241         int j;                                                              \
242         float in, res;                                                      \
243         in = *src0 * c->gain;                                               \
244         for(j = 0; j < c->order; j++)                                       \
245             in += c->cy[j] * s->x[j];                                       \
246         res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];    \
247         for(j = 1; j < c->order >> 1; j++)                                  \
248             res += (s->x[j] + s->x[c->order - j]) * c->cx[j];               \
249         for(j = 0; j < c->order - 1; j++)                                   \
250             s->x[j] = s->x[j + 1];                                          \
251         CONV_##fmt(*dst0, res)                                              \
252         s->x[c->order - 1] = in;                                            \
253         src0 += sstep;                                                      \
254         dst0 += dstep;                                                      \
255     }                                                                       \
256 }
257
258 void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
259                    struct FFIIRFilterState *s, int size,
260                    const int16_t *src, int sstep, int16_t *dst, int dstep)
261 {
262     if (c->order == 4) {
263         FILTER_BW_O4(int16_t, S16)
264     } else {
265         FILTER_DIRECT_FORM_II(int16_t, S16)
266     }
267 }
268
269 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
270                        struct FFIIRFilterState *s, int size,
271                        const float *src, int sstep, void *dst, int dstep)
272 {
273     if (c->order == 4) {
274         FILTER_BW_O4(float, FLT)
275     } else {
276         FILTER_DIRECT_FORM_II(float, FLT)
277     }
278 }
279
280 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
281 {
282     av_free(state);
283 }
284
285 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
286 {
287     if(coeffs){
288         av_free(coeffs->cx);
289         av_free(coeffs->cy);
290     }
291     av_free(coeffs);
292 }
293
294 #ifdef TEST
295 #define FILT_ORDER 4
296 #define SIZE 1024
297 int main(void)
298 {
299     struct FFIIRFilterCoeffs *fcoeffs = NULL;
300     struct FFIIRFilterState  *fstate  = NULL;
301     float cutoff_coeff = 0.4;
302     int16_t x[SIZE], y[SIZE];
303     int i;
304     FILE* fd;
305
306     fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
307                                         FF_FILTER_MODE_LOWPASS, FILT_ORDER,
308                                         cutoff_coeff, 0.0, 0.0);
309     fstate  = ff_iir_filter_init_state(FILT_ORDER);
310
311     for (i = 0; i < SIZE; i++) {
312         x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
313     }
314
315     ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
316
317     fd = fopen("in.bin", "w");
318     fwrite(x, sizeof(x[0]), SIZE, fd);
319     fclose(fd);
320
321     fd = fopen("out.bin", "w");
322     fwrite(y, sizeof(y[0]), SIZE, fd);
323     fclose(fd);
324
325     ff_iir_filter_free_coeffs(fcoeffs);
326     ff_iir_filter_free_state(fstate);
327     return 0;
328 }
329 #endif /* TEST */