libavcodec/iirfilter.c

   1 /*
   2  * IIR filter
   3  * Copyright (c) 2008 Konstantin Shishkov
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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) / 2.0)  / a0;
 141         x1       = (-(1.0 + cos_w0))        / a0;
 142     } else { // FF_FILTER_MODE_LOWPASS
 143         c->gain  =  ((1.0 - cos_w0) / 2.0)  / a0;
 144         x0       =  ((1.0 - cos_w0) / 2.0)  / a0;
 145         x1       =   (1.0 - cos_w0)         / a0;
 146     }
 147     c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
 148     c->cy[1] =  (2.0 *  cos_w0)        / 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     int ret = 0;
 168
 169     if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
 170         return NULL;
 171
 172     FF_ALLOCZ_OR_GOTO(avc, c,     sizeof(FFIIRFilterCoeffs),
 173                       init_fail);
 174     FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
 175                       init_fail);
 176     FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
 177                       init_fail);
 178     c->order = order;
 179
 180     switch (filt_type) {
 181     case FF_FILTER_TYPE_BUTTERWORTH:
 182         ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
 183                                       stopband);
 184         break;
 185     case FF_FILTER_TYPE_BIQUAD:
 186         ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
 187                                  stopband);
 188         break;
 189     default:
 190         av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
 191         goto init_fail;
 192     }
 193
 194     if (!ret)
 195         return c;
 196
 197 init_fail:
 198     ff_iir_filter_free_coeffs(c);
 199     return NULL;
 200 }
 201
 202 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
 203 {
 204     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
 205     return s;
 206 }
 207
 208 #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
 209
 210 #define CONV_FLT(dest, source) dest = source;
 211
 212 #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt)         \
 213     in = *src0 * c->gain                            \
 214          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]    \
 215          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3];   \
 216     res =  (s->x[i0] + in      )*1                  \
 217          + (s->x[i1] + s->x[i3])*4                  \
 218          +  s->x[i2]            *6;                 \
 219     CONV_##fmt(*dst0, res)                          \
 220     s->x[i0] = in;                                  \
 221     src0 += sstep;                                  \
 222     dst0 += dstep;
 223
 224 #define FILTER_BW_O4(type, fmt) {           \
 225     int i;                                  \
 226     const type *src0 = src;                 \
 227     type       *dst0 = dst;                 \
 228     for (i = 0; i < size; i += 4) {         \
 229         float in, res;                      \
 230         FILTER_BW_O4_1(0, 1, 2, 3, fmt);    \
 231         FILTER_BW_O4_1(1, 2, 3, 0, fmt);    \
 232         FILTER_BW_O4_1(2, 3, 0, 1, fmt);    \
 233         FILTER_BW_O4_1(3, 0, 1, 2, fmt);    \
 234     }                                       \
 235 }
 236
 237 #define FILTER_DIRECT_FORM_II(type, fmt) {                                  \
 238     int i;                                                                  \
 239     const type *src0 = src;                                                 \
 240     type       *dst0 = dst;                                                 \
 241     for (i = 0; i < size; i++) {                                            \
 242         int j;                                                              \
 243         float in, res;                                                      \
 244         in = *src0 * c->gain;                                               \
 245         for(j = 0; j < c->order; j++)                                       \
 246             in += c->cy[j] * s->x[j];                                       \
 247         res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];    \
 248         for(j = 1; j < c->order >> 1; j++)                                  \
 249             res += (s->x[j] + s->x[c->order - j]) * c->cx[j];               \
 250         for(j = 0; j < c->order - 1; j++)                                   \
 251             s->x[j] = s->x[j + 1];                                          \
 252         CONV_##fmt(*dst0, res)                                              \
 253         s->x[c->order - 1] = in;                                            \
 254         src0 += sstep;                                                      \
 255         dst0 += dstep;                                                      \
 256     }                                                                       \
 257 }
 258
 259 #define FILTER_O2(type, fmt) {                                              \
 260     int i;                                                                  \
 261     const type *src0 = src;                                                 \
 262     type       *dst0 = dst;                                                 \
 263     for (i = 0; i < size; i++) {                                            \
 264         float in = *src0   * c->gain  +                                     \
 265                    s->x[0] * c->cy[0] +                                     \
 266                    s->x[1] * c->cy[1];                                      \
 267         CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1])                \
 268         s->x[0] = s->x[1];                                                  \
 269         s->x[1] = in;                                                       \
 270         src0 += sstep;                                                      \
 271         dst0 += dstep;                                                      \
 272     }                                                                       \
 273 }
 274
 275 void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
 276                    struct FFIIRFilterState *s, int size,
 277                    const int16_t *src, int sstep, int16_t *dst, int dstep)
 278 {
 279     if (c->order == 2) {
 280         FILTER_O2(int16_t, S16)
 281     } else if (c->order == 4) {
 282         FILTER_BW_O4(int16_t, S16)
 283     } else {
 284         FILTER_DIRECT_FORM_II(int16_t, S16)
 285     }
 286 }
 287
 288 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
 289                        struct FFIIRFilterState *s, int size,
 290                        const float *src, int sstep, float *dst, int dstep)
 291 {
 292     if (c->order == 2) {
 293         FILTER_O2(float, FLT)
 294     } else if (c->order == 4) {
 295         FILTER_BW_O4(float, FLT)
 296     } else {
 297         FILTER_DIRECT_FORM_II(float, FLT)
 298     }
 299 }
 300
 301 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
 302 {
 303     av_free(state);
 304 }
 305
 306 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
 307 {
 308     if(coeffs){
 309         av_free(coeffs->cx);
 310         av_free(coeffs->cy);
 311     }
 312     av_free(coeffs);
 313 }
 314
 315 #ifdef TEST
 316 #define FILT_ORDER 4
 317 #define SIZE 1024
 318 int main(void)
 319 {
 320     struct FFIIRFilterCoeffs *fcoeffs = NULL;
 321     struct FFIIRFilterState  *fstate  = NULL;
 322     float cutoff_coeff = 0.4;
 323     int16_t x[SIZE], y[SIZE];
 324     int i;
 325     FILE* fd;
 326
 327     fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
 328                                         FF_FILTER_MODE_LOWPASS, FILT_ORDER,
 329                                         cutoff_coeff, 0.0, 0.0);
 330     fstate  = ff_iir_filter_init_state(FILT_ORDER);
 331
 332     for (i = 0; i < SIZE; i++) {
 333         x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
 334     }
 335
 336     ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
 337
 338     fd = fopen("in.bin", "w");
 339     fwrite(x, sizeof(x[0]), SIZE, fd);
 340     fclose(fd);
 341
 342     fd = fopen("out.bin", "w");
 343     fwrite(y, sizeof(y[0]), SIZE, fd);
 344     fclose(fd);
 345
 346     ff_iir_filter_free_coeffs(fcoeffs);
 347     ff_iir_filter_free_state(fstate);
 348     return 0;
 349 }
 350 #endif /* TEST */