/* * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <math.h>#include <stdint.h>#include <stdio.h> #include "libavutil/libm.h" #include "libavcodec/iirfilter.h"#include "libavcodec/iirfilter.c" #define FILT_ORDER 4#define SIZE 1024 static void iir_filter_int16(const struct FFIIRFilterCoeffs *c,                             struct FFIIRFilterState *s, int size,                             const int16_t *src, ptrdiff_t sstep,                             int16_t *dst, ptrdiff_t dstep){    if (c->order == 2) {        FILTER_O2(int16_t, S16)    } else if (c->order == 4) {        FILTER_BW_O4(int16_t, S16)    } else {        FILTER_DIRECT_FORM_II(int16_t, S16)    }} int main(void){    struct FFIIRFilterCoeffs *fcoeffs = NULL;    struct FFIIRFilterState  *fstate  = NULL;    float cutoff_coeff = 0.4;    int16_t x[SIZE], y[SIZE];    int i;     fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,                                        FF_FILTER_MODE_LOWPASS, FILT_ORDER,                                        cutoff_coeff, 0.0, 0.0);    fstate  = ff_iir_filter_init_state(FILT_ORDER);     for (i = 0; i < SIZE; i++)        x[i] = lrint(0.75 * INT16_MAX * sin(0.5 * M_PI * i * i / SIZE));     iir_filter_int16(fcoeffs, fstate, SIZE, x, 1, y, 1);     for (i = 0; i < SIZE; i++)        printf("%6d %6d\n", x[i], y[i]);     ff_iir_filter_free_coeffsp(&fcoeffs);    ff_iir_filter_free_statep(&fstate);    return 0;}