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libavcodec/iirfilter.c

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00001 /*
00002  * IIR filter
00003  * Copyright (c) 2008 Konstantin Shishkov
00004  *
00005  * This file is part of FFmpeg.
00006  *
00007  * FFmpeg is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * FFmpeg is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with FFmpeg; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00027 #include "iirfilter.h"
00028 #include <math.h>
00029 
00033 typedef struct FFIIRFilterCoeffs{
00034     int   order;
00035     float gain;
00036     int   *cx;
00037     float *cy;
00038 }FFIIRFilterCoeffs;
00039 
00043 typedef struct FFIIRFilterState{
00044     float x[1];
00045 }FFIIRFilterState;
00046 
00048 #define MAXORDER 30
00049 
00050 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
00051                                                     enum IIRFilterMode filt_mode,
00052                                                     int order, float cutoff_ratio,
00053                                                     float stopband, float ripple)
00054 {
00055     int i, j;
00056     FFIIRFilterCoeffs *c;
00057     double wa;
00058     double p[MAXORDER + 1][2];
00059 
00060     if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
00061         return NULL;
00062     if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
00063         return NULL;
00064 
00065     c = av_malloc(sizeof(FFIIRFilterCoeffs));
00066     c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
00067     c->cy = av_malloc(sizeof(c->cy[0]) * order);
00068     c->order = order;
00069 
00070     wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
00071 
00072     c->cx[0] = 1;
00073     for(i = 1; i < (order >> 1) + 1; i++)
00074         c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
00075 
00076     p[0][0] = 1.0;
00077     p[0][1] = 0.0;
00078     for(i = 1; i <= order; i++)
00079         p[i][0] = p[i][1] = 0.0;
00080     for(i = 0; i < order; i++){
00081         double zp[2];
00082         double th = (i + (order >> 1) + 0.5) * M_PI / order;
00083         double a_re, a_im, c_re, c_im;
00084         zp[0] = cos(th) * wa;
00085         zp[1] = sin(th) * wa;
00086         a_re = zp[0] + 2.0;
00087         c_re = zp[0] - 2.0;
00088         a_im =
00089         c_im = zp[1];
00090         zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
00091         zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
00092 
00093         for(j = order; j >= 1; j--)
00094         {
00095             a_re = p[j][0];
00096             a_im = p[j][1];
00097             p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
00098             p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
00099         }
00100         a_re    = p[0][0]*zp[0] - p[0][1]*zp[1];
00101         p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
00102         p[0][0] = a_re;
00103     }
00104     c->gain = p[order][0];
00105     for(i = 0; i < order; i++){
00106         c->gain += p[i][0];
00107         c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
00108                    (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
00109     }
00110     c->gain /= 1 << order;
00111 
00112     return c;
00113 }
00114 
00115 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
00116 {
00117     FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
00118     return s;
00119 }
00120 
00121 #define FILTER(i0, i1, i2, i3)                    \
00122     in =   *src * c->gain                         \
00123          + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]  \
00124          + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
00125     res =  (s->x[i0] + in      )*1                \
00126          + (s->x[i1] + s->x[i3])*4                \
00127          +  s->x[i2]            *6;               \
00128     *dst = av_clip_int16(lrintf(res));            \
00129     s->x[i0] = in;                                \
00130     src += sstep;                                 \
00131     dst += dstep;                                 \
00132 
00133 void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
00134 {
00135     int i;
00136 
00137     if(c->order == 4){
00138         for(i = 0; i < size; i += 4){
00139             float in, res;
00140 
00141             FILTER(0, 1, 2, 3);
00142             FILTER(1, 2, 3, 0);
00143             FILTER(2, 3, 0, 1);
00144             FILTER(3, 0, 1, 2);
00145         }
00146     }else{
00147         for(i = 0; i < size; i++){
00148             int j;
00149             float in, res;
00150             in = *src * c->gain;
00151             for(j = 0; j < c->order; j++)
00152                 in += c->cy[j] * s->x[j];
00153             res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
00154             for(j = 1; j < c->order >> 1; j++)
00155                 res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
00156             for(j = 0; j < c->order - 1; j++)
00157                 s->x[j] = s->x[j + 1];
00158             *dst = av_clip_int16(lrintf(res));
00159             s->x[c->order - 1] = in;
00160             src += sstep;
00161             dst += sstep;
00162         }
00163     }
00164 }
00165 
00166 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
00167 {
00168     av_free(state);
00169 }
00170 
00171 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
00172 {
00173     if(coeffs){
00174         av_free(coeffs->cx);
00175         av_free(coeffs->cy);
00176     }
00177     av_free(coeffs);
00178 }
00179 
00180 #ifdef TEST
00181 #define FILT_ORDER 4
00182 #define SIZE 1024
00183 int main(void)
00184 {
00185     struct FFIIRFilterCoeffs *fcoeffs = NULL;
00186     struct FFIIRFilterState  *fstate  = NULL;
00187     float cutoff_coeff = 0.4;
00188     int16_t x[SIZE], y[SIZE];
00189     int i;
00190     FILE* fd;
00191 
00192     fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
00193                                         FF_FILTER_MODE_LOWPASS, FILT_ORDER,
00194                                         cutoff_coeff, 0.0, 0.0);
00195     fstate  = ff_iir_filter_init_state(FILT_ORDER);
00196 
00197     for (i = 0; i < SIZE; i++) {
00198         x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
00199     }
00200 
00201     ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
00202 
00203     fd = fopen("in.bin", "w");
00204     fwrite(x, sizeof(x[0]), SIZE, fd);
00205     fclose(fd);
00206 
00207     fd = fopen("out.bin", "w");
00208     fwrite(y, sizeof(y[0]), SIZE, fd);
00209     fclose(fd);
00210 
00211     ff_iir_filter_free_coeffs(fcoeffs);
00212     ff_iir_filter_free_state(fstate);
00213     return 0;
00214 }
00215 #endif /* TEST */

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