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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 /**
23  * @file
24  * different IIR filters implementation
25  */
26 
27 #include "iirfilter.h"
28 #include <math.h>
29 #include "libavutil/attributes.h"
30 #include "libavutil/common.h"
31 
32 /**
33  * IIR filter global parameters
34  */
35 typedef struct FFIIRFilterCoeffs{
36  int order;
37  float gain;
38  int *cx;
39  float *cy;
40 }FFIIRFilterCoeffs;
41 
42 /**
43  * IIR filter state
44  */
45 typedef struct FFIIRFilterState{
46  float x[1];
47 }FFIIRFilterState;
48 
49 /// maximum supported filter order
50 #define MAXORDER 30
51 
52 static av_cold int butterworth_init_coeffs(void *avc,
53  struct FFIIRFilterCoeffs *c,
54  enum IIRFilterMode filt_mode,
55  int order, float cutoff_ratio,
56  float stopband)
57 {
58  int i, j;
59  double wa;
60  double p[MAXORDER + 1][2];
61 
62  if (filt_mode != FF_FILTER_MODE_LOWPASS) {
63  av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
64  "low-pass filter mode\n");
65  return -1;
66  }
67  if (order & 1) {
68  av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
69  "even filter orders\n");
70  return -1;
71  }
72 
73  wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
74 
75  c->cx[0] = 1;
76  for(i = 1; i < (order >> 1) + 1; i++)
77  c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
78 
79  p[0][0] = 1.0;
80  p[0][1] = 0.0;
81  for(i = 1; i <= order; i++)
82  p[i][0] = p[i][1] = 0.0;
83  for(i = 0; i < order; i++){
84  double zp[2];
85  double th = (i + (order >> 1) + 0.5) * M_PI / order;
86  double a_re, a_im, c_re, c_im;
87  zp[0] = cos(th) * wa;
88  zp[1] = sin(th) * wa;
89  a_re = zp[0] + 2.0;
90  c_re = zp[0] - 2.0;
91  a_im =
92  c_im = zp[1];
93  zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
94  zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
95 
96  for(j = order; j >= 1; j--)
97  {
98  a_re = p[j][0];
99  a_im = p[j][1];
100  p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
101  p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
102  }
103  a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
104  p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
105  p[0][0] = a_re;
106  }
107  c->gain = p[order][0];
108  for(i = 0; i < order; i++){
109  c->gain += p[i][0];
110  c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
111  (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
112  }
113  c->gain /= 1 << order;
114 
115  return 0;
116 }
117 
118 static av_cold int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
119  enum IIRFilterMode filt_mode, int order,
120  float cutoff_ratio, float stopband)
121 {
122  double cos_w0, sin_w0;
123  double a0, x0, x1;
124 
125  if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
126  filt_mode != FF_FILTER_MODE_LOWPASS) {
127  av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
128  "high-pass and low-pass filter modes\n");
129  return -1;
130  }
131  if (order != 2) {
132  av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
133  return -1;
134  }
135 
136  cos_w0 = cos(M_PI * cutoff_ratio);
137  sin_w0 = sin(M_PI * cutoff_ratio);
138 
139  a0 = 1.0 + (sin_w0 / 2.0);
140 
141  if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
142  c->gain = ((1.0 + cos_w0) / 2.0) / a0;
143  x0 = ((1.0 + cos_w0) / 2.0) / a0;
144  x1 = (-(1.0 + cos_w0)) / a0;
145  } else { // FF_FILTER_MODE_LOWPASS
146  c->gain = ((1.0 - cos_w0) / 2.0) / a0;
147  x0 = ((1.0 - cos_w0) / 2.0) / a0;
148  x1 = (1.0 - cos_w0) / a0;
149  }
150  c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
151  c->cy[1] = (2.0 * cos_w0) / a0;
152 
153  // divide by gain to make the x coeffs integers.
154  // during filtering, the delay state will include the gain multiplication
155  c->cx[0] = lrintf(x0 / c->gain);
156  c->cx[1] = lrintf(x1 / c->gain);
157 
158  return 0;
159 }
160 
161 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
162  enum IIRFilterType filt_type,
163  enum IIRFilterMode filt_mode,
164  int order, float cutoff_ratio,
165  float stopband, float ripple)
166 {
167  FFIIRFilterCoeffs *c;
168  int ret = 0;
169 
170  if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
171  return NULL;
172 
173  FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs),
174  init_fail);
175  FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
176  init_fail);
177  FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
178  init_fail);
179  c->order = order;
180 
181  switch (filt_type) {
182  case FF_FILTER_TYPE_BUTTERWORTH:
183  ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
184  stopband);
185  break;
186  case FF_FILTER_TYPE_BIQUAD:
187  ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
188  stopband);
189  break;
190  default:
191  av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
192  goto init_fail;
193  }
194 
195  if (!ret)
196  return c;
197 
198 init_fail:
199  ff_iir_filter_free_coeffs(c);
200  return NULL;
201 }
202 
203 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
204 {
205  FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
206  return s;
207 }
208 
209 #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
210 
211 #define CONV_FLT(dest, source) dest = source;
212 
213 #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \
214  in = *src0 * c->gain \
215  + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
216  + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
217  res = (s->x[i0] + in )*1 \
218  + (s->x[i1] + s->x[i3])*4 \
219  + s->x[i2] *6; \
220  CONV_##fmt(*dst0, res) \
221  s->x[i0] = in; \
222  src0 += sstep; \
223  dst0 += dstep;
224 
225 #define FILTER_BW_O4(type, fmt) { \
226  int i; \
227  const type *src0 = src; \
228  type *dst0 = dst; \
229  for (i = 0; i < size; i += 4) { \
230  float in, res; \
231  FILTER_BW_O4_1(0, 1, 2, 3, fmt); \
232  FILTER_BW_O4_1(1, 2, 3, 0, fmt); \
233  FILTER_BW_O4_1(2, 3, 0, 1, fmt); \
234  FILTER_BW_O4_1(3, 0, 1, 2, fmt); \
235  } \
236 }
237 
238 #define FILTER_DIRECT_FORM_II(type, fmt) { \
239  int i; \
240  const type *src0 = src; \
241  type *dst0 = dst; \
242  for (i = 0; i < size; i++) { \
243  int j; \
244  float in, res; \
245  in = *src0 * c->gain; \
246  for(j = 0; j < c->order; j++) \
247  in += c->cy[j] * s->x[j]; \
248  res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; \
249  for(j = 1; j < c->order >> 1; j++) \
250  res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; \
251  for(j = 0; j < c->order - 1; j++) \
252  s->x[j] = s->x[j + 1]; \
253  CONV_##fmt(*dst0, res) \
254  s->x[c->order - 1] = in; \
255  src0 += sstep; \
256  dst0 += dstep; \
257  } \
258 }
259 
260 #define FILTER_O2(type, fmt) { \
261  int i; \
262  const type *src0 = src; \
263  type *dst0 = dst; \
264  for (i = 0; i < size; i++) { \
265  float in = *src0 * c->gain + \
266  s->x[0] * c->cy[0] + \
267  s->x[1] * c->cy[1]; \
268  CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \
269  s->x[0] = s->x[1]; \
270  s->x[1] = in; \
271  src0 += sstep; \
272  dst0 += dstep; \
273  } \
274 }
275 
276 void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
277  struct FFIIRFilterState *s, int size,
278  const int16_t *src, int sstep, int16_t *dst, int dstep)
279 {
280  if (c->order == 2) {
281  FILTER_O2(int16_t, S16)
282  } else if (c->order == 4) {
283  FILTER_BW_O4(int16_t, S16)
284  } else {
285  FILTER_DIRECT_FORM_II(int16_t, S16)
286  }
287 }
288 
289 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
290  struct FFIIRFilterState *s, int size,
291  const float *src, int sstep, float *dst, int dstep)
292 {
293  if (c->order == 2) {
294  FILTER_O2(float, FLT)
295  } else if (c->order == 4) {
296  FILTER_BW_O4(float, FLT)
297  } else {
298  FILTER_DIRECT_FORM_II(float, FLT)
299  }
300 }
301 
302 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
303 {
304  av_free(state);
305 }
306 
307 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
308 {
309  if(coeffs){
310  av_free(coeffs->cx);
311  av_free(coeffs->cy);
312  }
313  av_free(coeffs);
314 }
315 
316 void ff_iir_filter_init(FFIIRFilterContext *f) {
317  f->filter_flt = ff_iir_filter_flt;
318 
319  if (HAVE_MIPSFPU)
320  ff_iir_filter_init_mips(f);
321 }
322 
323 #ifdef TEST
324 #include <stdio.h>
325 
326 #define FILT_ORDER 4
327 #define SIZE 1024
328 int main(void)
329 {
330  struct FFIIRFilterCoeffs *fcoeffs = NULL;
331  struct FFIIRFilterState *fstate = NULL;
332  float cutoff_coeff = 0.4;
333  int16_t x[SIZE], y[SIZE];
334  int i;
335 
336  fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,
337  FF_FILTER_MODE_LOWPASS, FILT_ORDER,
338  cutoff_coeff, 0.0, 0.0);
339  fstate = ff_iir_filter_init_state(FILT_ORDER);
340 
341  for (i = 0; i < SIZE; i++) {
342  x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
343  }
344 
345  ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
346 
347  for (i = 0; i < SIZE; i++)
348  printf("%6d %6d\n", x[i], y[i]);
349 
350  ff_iir_filter_free_coeffs(fcoeffs);
351  ff_iir_filter_free_state(fstate);
352  return 0;
353 }
354 #endif /* TEST */
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