Split out Butterworth filter coeff init to a separate function.
[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 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
116                                                 enum IIRFilterType filt_type,
117                                                 enum IIRFilterMode filt_mode,
118                                                 int order, float cutoff_ratio,
119                                                 float stopband, float ripple)
120 {
121     FFIIRFilterCoeffs *c;
122
123     if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
124         return NULL;
125
126     FF_ALLOCZ_OR_GOTO(avc, c,     sizeof(FFIIRFilterCoeffs),
127                       init_fail);
128     FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
129                       init_fail);
130     FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
131                       init_fail);
132     c->order = order;
133
134     if (filt_type == FF_FILTER_TYPE_BUTTERWORTH) {
135         if (butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
136             stopband)) {
137             goto init_fail;
138         }
139     } else {
140         av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
141         goto init_fail;
142     }
143
144     return c;
145
146 init_fail:
147     ff_iir_filter_free_coeffs(c);
148     return NULL;
149 }
150
151 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
152 {
153     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
154     return s;
155 }
156
157 #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
158
159 #define CONV_FLT(dest, source) dest = source;
160
161 #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt)         \
162     in = *src0 * c->gain                            \
163          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]    \
164          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3];   \
165     res =  (s->x[i0] + in      )*1                  \
166          + (s->x[i1] + s->x[i3])*4                  \
167          +  s->x[i2]            *6;                 \
168     CONV_##fmt(*dst0, res)                          \
169     s->x[i0] = in;                                  \
170     src0 += sstep;                                  \
171     dst0 += dstep;
172
173 #define FILTER_BW_O4(type, fmt) {           \
174     int i;                                  \
175     const type *src0 = src;                 \
176     type       *dst0 = dst;                 \
177     for (i = 0; i < size; i += 4) {         \
178         float in, res;                      \
179         FILTER_BW_O4_1(0, 1, 2, 3, fmt);    \
180         FILTER_BW_O4_1(1, 2, 3, 0, fmt);    \
181         FILTER_BW_O4_1(2, 3, 0, 1, fmt);    \
182         FILTER_BW_O4_1(3, 0, 1, 2, fmt);    \
183     }                                       \
184 }
185
186 #define FILTER_DIRECT_FORM_II(type, fmt) {                                  \
187     int i;                                                                  \
188     const type *src0 = src;                                                 \
189     type       *dst0 = dst;                                                 \
190     for (i = 0; i < size; i++) {                                            \
191         int j;                                                              \
192         float in, res;                                                      \
193         in = *src0 * c->gain;                                               \
194         for(j = 0; j < c->order; j++)                                       \
195             in += c->cy[j] * s->x[j];                                       \
196         res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];    \
197         for(j = 1; j < c->order >> 1; j++)                                  \
198             res += (s->x[j] + s->x[c->order - j]) * c->cx[j];               \
199         for(j = 0; j < c->order - 1; j++)                                   \
200             s->x[j] = s->x[j + 1];                                          \
201         CONV_##fmt(*dst0, res)                                              \
202         s->x[c->order - 1] = in;                                            \
203         src0 += sstep;                                                      \
204         dst0 += dstep;                                                      \
205     }                                                                       \
206 }
207
208 void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
209                    struct FFIIRFilterState *s, int size,
210                    const int16_t *src, int sstep, int16_t *dst, int dstep)
211 {
212     if (c->order == 4) {
213         FILTER_BW_O4(int16_t, S16)
214     } else {
215         FILTER_DIRECT_FORM_II(int16_t, S16)
216     }
217 }
218
219 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
220                        struct FFIIRFilterState *s, int size,
221                        const float *src, int sstep, void *dst, int dstep)
222 {
223     if (c->order == 4) {
224         FILTER_BW_O4(float, FLT)
225     } else {
226         FILTER_DIRECT_FORM_II(float, FLT)
227     }
228 }
229
230 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
231 {
232     av_free(state);
233 }
234
235 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
236 {
237     if(coeffs){
238         av_free(coeffs->cx);
239         av_free(coeffs->cy);
240     }
241     av_free(coeffs);
242 }
243
244 #ifdef TEST
245 #define FILT_ORDER 4
246 #define SIZE 1024
247 int main(void)
248 {
249     struct FFIIRFilterCoeffs *fcoeffs = NULL;
250     struct FFIIRFilterState  *fstate  = NULL;
251     float cutoff_coeff = 0.4;
252     int16_t x[SIZE], y[SIZE];
253     int i;
254     FILE* fd;
255
256     fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
257                                         FF_FILTER_MODE_LOWPASS, FILT_ORDER,
258                                         cutoff_coeff, 0.0, 0.0);
259     fstate  = ff_iir_filter_init_state(FILT_ORDER);
260
261     for (i = 0; i < SIZE; i++) {
262         x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
263     }
264
265     ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
266
267     fd = fopen("in.bin", "w");
268     fwrite(x, sizeof(x[0]), SIZE, fd);
269     fclose(fd);
270
271     fd = fopen("out.bin", "w");
272     fwrite(y, sizeof(y[0]), SIZE, fd);
273     fclose(fd);
274
275     ff_iir_filter_free_coeffs(fcoeffs);
276     ff_iir_filter_free_state(fstate);
277     return 0;
278 }
279 #endif /* TEST */