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/* 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>

#include <spa/utils/defs.h>

#ifndef SPA_API_DLL

 #ifdef SPA_API_IMPL

  #define SPA_API_DLL SPA_API_IMPL

 #else

  #define SPA_API_DLL static inline

 #endif

#endif

#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;

};

SPA_API_DLL void spa_dll_init(struct spa_dll *dll)

	dll->bw = 0.0;

	dll->z1 = dll->z2 = dll->z3 = 0.0;

SPA_API_DLL 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;

SPA_API_DLL 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 */