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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
  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 */