dll.h

/* Simple DLL */
/* SPDX-FileCopyrightText: Copyright © 2019 Wim Taymans */
/* SPDX-License-Identifier: MIT */
 
#ifndef SPA_DLL_H
#define SPA_DLL_H
 
#ifdef __cplusplus
extern "C" {
#endif
 
#include <stddef.h>
#include <math.h>
 
#define SPA_DLL_BW_MAX          0.128
#define SPA_DLL_BW_MIN          0.016
 
struct spa_dll {
        double bw;
        double z1, z2, z3;
        double w0, w1, w2;
};
 
static inline void spa_dll_init(struct spa_dll *dll)
{
        dll->bw = 0.0;
        dll->z1 = dll->z2 = dll->z3 = 0.0;
}
 
static inline void spa_dll_set_bw(struct spa_dll *dll, double bw, unsigned period, unsigned rate)
{
        double w = 2 * M_PI * bw * period / rate;
        dll->w0 = 1.0 - exp (-20.0 * w);
        dll->w1 = w * 1.5 / period;
        dll->w2 = w / 1.5;
        dll->bw = bw;
}
 
static inline double spa_dll_update(struct spa_dll *dll, double err)
{
        dll->z1 += dll->w0 * (dll->w1 * err - dll->z1);
        dll->z2 += dll->w0 * (dll->z1 - dll->z2);
        dll->z3 += dll->w2 * dll->z2;
        return 1.0 - (dll->z2 + dll->z3);
}
 
#ifdef __cplusplus
} /* extern "C" */
#endif
 
#endif /* SPA_DLL_H */