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 iirfilter.c
  24  * different IIR filters implementation
  25  */
  26
  27 #include "iirfilter.h"
  28 #include <complex.h>
  29 #include <math.h>
  30
  31 /**
  32  * IIR filter global parameters
  33  */
  34 typedef struct FFIIRFilterCoeffs{
  35     int   order;
  36     float gain;
  37     int   *cx;
  38     float *cy;
  39 }FFIIRFilterCoeffs;
  40
  41 /**
  42  * IIR filter state
  43  */
  44 typedef struct FFIIRFilterState{
  45     float x[1];
  46 }FFIIRFilterState;
  47
  48 /// maximum supported filter order
  49 #define MAXORDER 30
  50
  51 struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
  52                                                     enum IIRFilterMode filt_mode,
  53                                                     int order, float cutoff_ratio,
  54                                                     float stopband, float ripple)
  55 {
  56     int i, j, size;
  57     FFIIRFilterCoeffs *c;
  58     double wa;
  59     complex p[MAXORDER + 1];
  60
  61     if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
  62         return NULL;
  63     if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
  64         return NULL;
  65
  66     c = av_malloc(sizeof(FFIIRFilterCoeffs));
  67     c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
  68     c->cy = av_malloc(sizeof(c->cy[0]) * order);
  69     c->order = order;
  70
  71     wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
  72
  73     c->cx[0] = 1;
  74     for(i = 1; i < (order >> 1) + 1; i++)
  75         c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
  76
  77     p[0] = 1.0;
  78     for(i = 1; i <= order; i++)
  79         p[i] = 0.0;
  80     for(i = 0; i < order; i++){
  81         complex zp;
  82         double th = (i + (order >> 1) + 0.5) * M_PI / order;
  83         zp = cexp(I*th) * wa;
  84         zp = (zp + 2.0) / (zp - 2.0);
  85
  86         for(j = order; j >= 1; j--)
  87             p[j] = zp*p[j] + p[j - 1];
  88         p[0] *= zp;
  89     }
  90     c->gain = creal(p[order]);
  91     for(i = 0; i < order; i++){
  92         c->gain += creal(p[i]);
  93         c->cy[i] = creal(-p[i] / p[order]);
  94     }
  95     c->gain /= 1 << order;
  96
  97     return c;
  98 }
  99
 100 struct FFIIRFilterState* ff_iir_filter_init_state(int order)
 101 {
 102     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
 103     return s;
 104 }
 105
 106 #define FILTER(i0, i1, i2, i3)                    \
 107     in =   *src * c->gain                         \
 108          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]  \
 109          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
 110     res =  (s->x[i0] + in      )*1                \
 111          + (s->x[i1] + s->x[i3])*4                \
 112          +  s->x[i2]            *6;               \
 113     *dst = av_clip_int16(lrintf(res));            \
 114     s->x[i0] = in;                                \
 115     src += sstep;                                 \
 116     dst += dstep;                                 \
 117
 118 void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
 119 {
 120     int i;
 121
 122     if(c->order == 4){
 123         for(i = 0; i < size; i += 4){
 124             float in, res;
 125
 126             FILTER(0, 1, 2, 3);
 127             FILTER(1, 2, 3, 0);
 128             FILTER(2, 3, 0, 1);
 129             FILTER(3, 0, 1, 2);
 130         }
 131     }else{
 132         for(i = 0; i < size; i++){
 133             int j;
 134             float in, res;
 135             in = *src * c->gain;
 136             for(j = 0; j < c->order; j++)
 137                 in += c->cy[j] * s->x[j];
 138             res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
 139             for(j = 1; j < c->order >> 1; j++)
 140                 res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
 141             for(j = 0; j < c->order - 1; j++)
 142                 s->x[j] = s->x[j + 1];
 143             *dst = av_clip_int16(lrintf(res));
 144             s->x[c->order - 1] = in;
 145             src += sstep;
 146             dst += sstep;
 147         }
 148     }
 149 }
 150
 151 void ff_iir_filter_free_state(struct FFIIRFilterState *state)
 152 {
 153     av_free(state);
 154 }
 155
 156 void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
 157 {
 158     if(coeffs){
 159         av_free(coeffs->cx);
 160         av_free(coeffs->cy);
 161     }
 162     av_free(coeffs);
 163 }
 164