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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 <math.h>
  28
  29 #include "libavutil/attributes.h"
  30 #include "libavutil/common.h"
  31
  32 #include "iirfilter.h"
  33
  34 /**
  35  * IIR filter global parameters
  36  */
  37 typedef struct FFIIRFilterCoeffs {
  38     int   order;
  39     float gain;
  40     int   *cx;
  41     float *cy;
  42 } FFIIRFilterCoeffs;
  43
  44 /**
  45  * IIR filter state
  46  */
  47 typedef struct FFIIRFilterState {
  48     float x[1];
  49 } FFIIRFilterState;
  50
  51 /// maximum supported filter order
  52 #define MAXORDER 30
  53
  54 static av_cold int butterworth_init_coeffs(void *avc,
  55                                            struct FFIIRFilterCoeffs *c,
  56                                            enum IIRFilterMode filt_mode,
  57                                            int order, float cutoff_ratio,
  58                                            float stopband)
  59 {
  60     int i, j;
  61     double wa;
  62     double p[MAXORDER + 1][2];
  63
  64     if (filt_mode != FF_FILTER_MODE_LOWPASS) {
  65         av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
  66                                   "low-pass filter mode\n");
  67         return -1;
  68     }
  69     if (order & 1) {
  70         av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
  71                                   "even filter orders\n");
  72         return -1;
  73     }
  74
  75     wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
  76
  77     c->cx[0] = 1;
  78     for (i = 1; i < (order >> 1) + 1; i++)
  79         c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
  80
  81     p[0][0] = 1.0;
  82     p[0][1] = 0.0;
  83     for (i = 1; i <= order; i++)
  84         p[i][0] = p[i][1] = 0.0;
  85     for (i = 0; i < order; i++) {
  86         double zp[2];
  87         double th = (i + (order >> 1) + 0.5) * M_PI / order;
  88         double a_re, a_im, c_re, c_im;
  89         zp[0] = cos(th) * wa;
  90         zp[1] = sin(th) * wa;
  91         a_re  = zp[0] + 2.0;
  92         c_re  = zp[0] - 2.0;
  93         a_im  =
  94         c_im  = zp[1];
  95         zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
  96         zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
  97
  98         for (j = order; j >= 1; j--) {
  99             a_re    = p[j][0];
 100             a_im    = p[j][1];
 101             p[j][0] = a_re * zp[0] - a_im * zp[1] + p[j - 1][0];
 102             p[j][1] = a_re * zp[1] + a_im * zp[0] + p[j - 1][1];
 103         }
 104         a_re    = p[0][0] * zp[0] - p[0][1] * zp[1];
 105         p[0][1] = p[0][0] * zp[1] + p[0][1] * zp[0];
 106         p[0][0] = a_re;
 107     }
 108     c->gain = p[order][0];
 109     for (i = 0; i < order; i++) {
 110         c->gain += p[i][0];
 111         c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
 112                    (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
 113     }
 114     c->gain /= 1 << order;
 115
 116     return 0;
 117 }
 118
 119 static av_cold int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
 120                                       enum IIRFilterMode filt_mode, int order,
 121                                       float cutoff_ratio, float stopband)
 122 {
 123     double cos_w0, sin_w0;
 124     double a0, x0, x1;
 125
 126     if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
 127         filt_mode != FF_FILTER_MODE_LOWPASS) {
 128         av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
 129                                   "high-pass and low-pass filter modes\n");
 130         return -1;
 131     }
 132     if (order != 2) {
 133         av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
 134         return -1;
 135     }
 136
 137     cos_w0 = cos(M_PI * cutoff_ratio);
 138     sin_w0 = sin(M_PI * cutoff_ratio);
 139
 140     a0 = 1.0 + (sin_w0 / 2.0);
 141
 142     if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
 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     } else { // FF_FILTER_MODE_LOWPASS
 147         c->gain  =  ((1.0 - cos_w0) / 2.0)  / a0;
 148         x0       =  ((1.0 - cos_w0) / 2.0)  / a0;
 149         x1       =   (1.0 - cos_w0)         / a0;
 150     }
 151     c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
 152     c->cy[1] =  (2.0 *  cos_w0)        / a0;
 153
 154     // divide by gain to make the x coeffs integers.
 155     // during filtering, the delay state will include the gain multiplication
 156     c->cx[0] = lrintf(x0 / c->gain);
 157     c->cx[1] = lrintf(x1 / c->gain);
 158
 159     return 0;
 160 }
 161
 162 av_cold struct FFIIRFilterCoeffs *ff_iir_filter_init_coeffs(void *avc,
 163                                                             enum IIRFilterType filt_type,
 164                                                             enum IIRFilterMode filt_mode,
 165                                                             int order, float cutoff_ratio,
 166                                                             float stopband, float ripple)
 167 {
 168     FFIIRFilterCoeffs *c;
 169     int ret = 0;
 170
 171     if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
 172         return NULL;
 173
 174     if (!(c     = av_mallocz(sizeof(*c)))                            ||
 175         !(c->cx = av_malloc (sizeof(c->cx[0]) * ((order >> 1) + 1))) ||
 176         !(c->cy = av_malloc (sizeof(c->cy[0]) * order)))
 177         goto free;
 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 free;
 192     }
 193
 194     if (!ret)
 195         return c;
 196 free:
 197     ff_iir_filter_free_coeffsp(&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] +                          \
 214          c->cy[1] * s->x[i1] +                          \
 215          c->cy[2] * s->x[i2] +                          \
 216          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, ptrdiff_t sstep,
 279                    int16_t *dst, ptrdiff_t dstep)
 280 {
 281     if (c->order == 2) {
 282         FILTER_O2(int16_t, S16)
 283     } else if (c->order == 4) {
 284         FILTER_BW_O4(int16_t, S16)
 285     } else {
 286         FILTER_DIRECT_FORM_II(int16_t, S16)
 287     }
 288 }
 289
 290 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
 291                        struct FFIIRFilterState *s, int size,
 292                        const float *src, ptrdiff_t sstep,
 293                        float *dst, ptrdiff_t dstep)
 294 {
 295     if (c->order == 2) {
 296         FILTER_O2(float, FLT)
 297     } else if (c->order == 4) {
 298         FILTER_BW_O4(float, FLT)
 299     } else {
 300         FILTER_DIRECT_FORM_II(float, FLT)
 301     }
 302 }
 303
 304 av_cold void ff_iir_filter_free_statep(struct FFIIRFilterState **state)
 305 {
 306     av_freep(state);
 307 }
 308
 309 av_cold void ff_iir_filter_free_coeffsp(struct FFIIRFilterCoeffs **coeffsp)
 310 {
 311     struct FFIIRFilterCoeffs *coeffs = *coeffsp;
 312     if (coeffs) {
 313         av_freep(&coeffs->cx);
 314         av_freep(&coeffs->cy);
 315     }
 316     av_freep(coeffsp);
 317 }
 318
 319 void ff_iir_filter_init(FFIIRFilterContext *f) {
 320     f->filter_flt = ff_iir_filter_flt;
 321
 322     if (HAVE_MIPSFPU)
 323         ff_iir_filter_init_mips(f);
 324 }