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ffmpeg / libavcodec / iirfilter.c @ c3897d76

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/*
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 * IIR filter
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 * Copyright (c) 2008 Konstantin Shishkov
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/**
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 * @file
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 * different IIR filters implementation
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 */
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#include "iirfilter.h"
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#include <math.h>
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/**
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 * IIR filter global parameters
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 */
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typedef struct FFIIRFilterCoeffs{
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    int   order;
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    float gain;
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    int   *cx;
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    float *cy;
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}FFIIRFilterCoeffs;
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/**
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 * IIR filter state
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 */
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typedef struct FFIIRFilterState{
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    float x[1];
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}FFIIRFilterState;
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/// maximum supported filter order
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#define MAXORDER 30
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av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
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                                                    enum IIRFilterMode filt_mode,
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                                                    int order, float cutoff_ratio,
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                                                    float stopband, float ripple)
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{
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    int i, j;
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    FFIIRFilterCoeffs *c;
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    double wa;
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    double p[MAXORDER + 1][2];
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    if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
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        return NULL;
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    if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
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        return NULL;
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    c = av_malloc(sizeof(FFIIRFilterCoeffs));
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    c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
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    c->cy = av_malloc(sizeof(c->cy[0]) * order);
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    c->order = order;
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    wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
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    c->cx[0] = 1;
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    for(i = 1; i < (order >> 1) + 1; i++)
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        c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
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    p[0][0] = 1.0;
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    p[0][1] = 0.0;
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    for(i = 1; i <= order; i++)
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        p[i][0] = p[i][1] = 0.0;
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    for(i = 0; i < order; i++){
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        double zp[2];
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        double th = (i + (order >> 1) + 0.5) * M_PI / order;
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        double a_re, a_im, c_re, c_im;
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        zp[0] = cos(th) * wa;
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        zp[1] = sin(th) * wa;
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        a_re = zp[0] + 2.0;
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        c_re = zp[0] - 2.0;
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        a_im =
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        c_im = zp[1];
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        zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
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        zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
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        for(j = order; j >= 1; j--)
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        {
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            a_re = p[j][0];
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            a_im = p[j][1];
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            p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
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            p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
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        }
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        a_re    = p[0][0]*zp[0] - p[0][1]*zp[1];
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        p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
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        p[0][0] = a_re;
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    }
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    c->gain = p[order][0];
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    for(i = 0; i < order; i++){
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        c->gain += p[i][0];
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        c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
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                   (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
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    }
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    c->gain /= 1 << order;
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    return c;
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}
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av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
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{
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    FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
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    return s;
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}
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#define FILTER(i0, i1, i2, i3)                    \
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    in =   *src * c->gain                         \
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         + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]  \
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         + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
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    res =  (s->x[i0] + in      )*1                \
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         + (s->x[i1] + s->x[i3])*4                \
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         +  s->x[i2]            *6;               \
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    *dst = av_clip_int16(lrintf(res));            \
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    s->x[i0] = in;                                \
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    src += sstep;                                 \
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    dst += dstep;                                 \
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void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
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{
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    int i;
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    if(c->order == 4){
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        for(i = 0; i < size; i += 4){
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            float in, res;
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            FILTER(0, 1, 2, 3);
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            FILTER(1, 2, 3, 0);
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            FILTER(2, 3, 0, 1);
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            FILTER(3, 0, 1, 2);
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        }
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    }else{
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        for(i = 0; i < size; i++){
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            int j;
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            float in, res;
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            in = *src * c->gain;
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            for(j = 0; j < c->order; j++)
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                in += c->cy[j] * s->x[j];
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            res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
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            for(j = 1; j < c->order >> 1; j++)
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                res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
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            for(j = 0; j < c->order - 1; j++)
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                s->x[j] = s->x[j + 1];
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            *dst = av_clip_int16(lrintf(res));
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            s->x[c->order - 1] = in;
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            src += sstep;
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            dst += dstep;
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        }
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    }
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}
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av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
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{
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    av_free(state);
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}
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av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
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{
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    if(coeffs){
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        av_free(coeffs->cx);
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        av_free(coeffs->cy);
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    }
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    av_free(coeffs);
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}
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#ifdef TEST
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#define FILT_ORDER 4
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#define SIZE 1024
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int main(void)
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{
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    struct FFIIRFilterCoeffs *fcoeffs = NULL;
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    struct FFIIRFilterState  *fstate  = NULL;
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    float cutoff_coeff = 0.4;
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    int16_t x[SIZE], y[SIZE];
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    int i;
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    FILE* fd;
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    fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
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                                        FF_FILTER_MODE_LOWPASS, FILT_ORDER,
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                                        cutoff_coeff, 0.0, 0.0);
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    fstate  = ff_iir_filter_init_state(FILT_ORDER);
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    for (i = 0; i < SIZE; i++) {
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        x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
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    }
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    ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
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    fd = fopen("in.bin", "w");
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    fwrite(x, sizeof(x[0]), SIZE, fd);
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    fclose(fd);
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    fd = fopen("out.bin", "w");
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    fwrite(y, sizeof(y[0]), SIZE, fd);
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    fclose(fd);
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    ff_iir_filter_free_coeffs(fcoeffs);
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    ff_iir_filter_free_state(fstate);
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    return 0;
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}
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#endif /* TEST */