/* * Opus encoder * Copyright (c) 2017 Rostislav Pehlivanov <atomnuker@gmail.com> * * 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 */ #ifndef AVCODEC_OPUS_ENC_UTILS_H#define AVCODEC_OPUS_ENC_UTILS_H #include <math.h>#include <string.h> #include "opus.h" typedef struct FFBesselFilter {    float a[3];    float b[2];    float x[3];    float y[3];} FFBesselFilter; /* Fills the coefficients, returns 1 if filter will be unstable */static inline int bessel_reinit(FFBesselFilter *s, float n, float f0, float fs,                                int highpass){    int unstable;    float c, cfreq, w0, k1, k2;     if (!highpass) {        c = (1.0f/sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f))/sqrtf(3.0f);        cfreq = c*f0/fs;        unstable = (cfreq <= 0.0f || cfreq >= 1.0f/4.0f);    } else {        c = sqrtf(3.0f)*sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f);        cfreq = 0.5f - c*f0/fs;        unstable = (cfreq <= 3.0f/8.0f || cfreq >= 1.0f/2.0f);    }     w0 = tanf(M_PI*cfreq);    k1 = 3.0f * w0;    k2 = 3.0f * w0;     s->a[0] = k2/(1.0f + k1 + k2);    s->a[1] = 2.0f * s->a[0];    s->a[2] = s->a[0];    s->b[0] = 2.0f * s->a[0] * (1.0f/k2 - 1.0f);    s->b[1] = 1.0f - (s->a[0] + s->a[1] + s->a[2] + s->b[0]);     if (highpass) {        s->a[1] *= -1;        s->b[0] *= -1;    }     return unstable;} static inline int bessel_init(FFBesselFilter *s, float n, float f0, float fs,                              int highpass){    memset(s, 0, sizeof(FFBesselFilter));    return bessel_reinit(s, n, f0, fs, highpass);} static inline float bessel_filter(FFBesselFilter *s, float x){    s->x[2] = s->x[1];    s->x[1] = s->x[0];    s->x[0] = x;    s->y[2] = s->y[1];    s->y[1] = s->y[0];    s->y[0] = s->a[0]*s->x[0] + s->a[1]*s->x[1] + s->a[2]*s->x[2] + s->b[0]*s->y[1] + s->b[1]*s->y[2];    return s->y[0];} #endif /* AVCODEC_OPUS_ENC_UTILS_H */