/* Simple DLL
 *
 * Copyright © 2019 Wim Taymans
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#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 */