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 libavcodec/iirfilter.c
  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 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
  51                                                     enum IIRFilterMode filt_mode,
  52                                                     int order, float cutoff_ratio,
  53                                                     float stopband, float ripple)
  54 {
  55     int i, j;
  56     FFIIRFilterCoeffs *c;
  57     double wa;
  58     double p[MAXORDER + 1][2];
  59
  60     if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
  61         return NULL;
  62     if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
  63         return NULL;
  64
  65     c = av_malloc(sizeof(FFIIRFilterCoeffs));
  66     c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
  67     c->cy = av_malloc(sizeof(c->cy[0]) * order);
  68     c->order = order;
  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 c;
 113 }
 114
 115 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
 116 {
 117     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
 118     return s;
 119 }
 120
 121 #define FILTER(i0, i1, i2, i3)                    \
 122     in =   *src * c->gain                         \
 123          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]  \
 124          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
 125     res =  (s->x[i0] + in      )*1                \
 126          + (s->x[i1] + s->x[i3])*4                \
 127          +  s->x[i2]            *6;               \
 128     *dst = av_clip_int16(lrintf(res));            \
 129     s->x[i0] = in;                                \
 130     src += sstep;                                 \
 131     dst += dstep;                                 \
 132
 133 void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
 134 {
 135     int i;
 136
 137     if(c->order == 4){
 138         for(i = 0; i < size; i += 4){
 139             float in, res;
 140
 141             FILTER(0, 1, 2, 3);
 142             FILTER(1, 2, 3, 0);
 143             FILTER(2, 3, 0, 1);
 144             FILTER(3, 0, 1, 2);
 145         }
 146     }else{
 147         for(i = 0; i < size; i++){
 148             int j;
 149             float in, res;
 150             in = *src * c->gain;
 151             for(j = 0; j < c->order; j++)
 152                 in += c->cy[j] * s->x[j];
 153             res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
 154             for(j = 1; j < c->order >> 1; j++)
 155                 res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
 156             for(j = 0; j < c->order - 1; j++)
 157                 s->x[j] = s->x[j + 1];
 158             *dst = av_clip_int16(lrintf(res));
 159             s->x[c->order - 1] = in;
 160             src += sstep;
 161             dst += sstep;
 162         }
 163     }
 164 }
 165
 166 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
 167 {
 168     av_free(state);
 169 }
 170
 171 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
 172 {
 173     if(coeffs){
 174         av_free(coeffs->cx);
 175         av_free(coeffs->cy);
 176     }
 177     av_free(coeffs);
 178 }
 179
 180 #ifdef TEST
 181 #define FILT_ORDER 4
 182 #define SIZE 1024
 183 int main(void)
 184 {
 185     struct FFIIRFilterCoeffs *fcoeffs = NULL;
 186     struct FFIIRFilterState  *fstate  = NULL;
 187     float cutoff_coeff = 0.4;
 188     int16_t x[SIZE], y[SIZE];
 189     int i;
 190     FILE* fd;
 191
 192     fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
 193                                         FF_FILTER_MODE_LOWPASS, FILT_ORDER,
 194                                         cutoff_coeff, 0.0, 0.0);
 195     fstate  = ff_iir_filter_init_state(FILT_ORDER);
 196
 197     for (i = 0; i < SIZE; i++) {
 198         x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
 199     }
 200
 201     ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
 202
 203     fd = fopen("in.bin", "w");
 204     fwrite(x, sizeof(x[0]), SIZE, fd);
 205     fclose(fd);
 206
 207     fd = fopen("out.bin", "w");
 208     fwrite(y, sizeof(y[0]), SIZE, fd);
 209     fclose(fd);
 210
 211     ff_iir_filter_free_coeffs(fcoeffs);
 212     ff_iir_filter_free_state(fstate);
 213     return 0;
 214 }
 215 #endif /* TEST */