/*
 * Copyright (C) 2017 Robin Gareus <robin@gareus.org>
 * Copyright (C) 1999 Paul Davis
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

#ifndef __pbd_control_math_h__
#define __pbd_control_math_h__

#include <assert.h>
#include <math.h>
#include <stdint.h>

/* map gain-coeff [0..2] to position [0..1] */
static inline double
gain_to_position (double g)
{
	if (g == 0) {
		return 0;
	}
	return pow ((6.0 * log (g) / log (2.0) + 192.0) / 198.0, 8.0);
}

/* map position [0..1] to gain-coeff [0..2] */
static inline double
position_to_gain (double pos)
{
	if (pos == 0.0) {
		return 0.0;
	}
	return exp (((pow (pos, 1.0 / 8.0) * 198.0) - 192.0) / 6.0 * log (2.0));
}

/* map position [0..1] to parameter [lower..upper] on a logarithmic scale */
static inline double
position_to_logscale (double pos, double lower, double upper)
{
	assert (upper > lower && lower * upper > 0);
	assert (pos >= 0.0 && pos <= 1.0);
	return lower * pow (upper / lower, pos);
}

/* map parameter [lower..upper] to position [0..1] on a logarithmic scale*/
static inline double
logscale_to_position (double val, double lower, double upper)
{
	assert (upper > lower && lower * upper > 0);
	assert (val >= lower && val <= upper);
	return log (val / lower) / log (upper / lower);
}

static inline double
logscale_to_position_with_steps (double val, double lower, double upper, uint32_t steps)
{
	assert (steps > 1);
	double v = logscale_to_position (val, lower, upper) * (steps - 1.0);
	return round (v) / (steps - 1.0);
}

static inline double
position_to_logscale_with_steps (double pos, double lower, double upper, uint32_t steps)
{
	assert (steps > 1);
	double p = round (pos * (steps - 1.0)) / (steps - 1.0);
	return position_to_logscale (p, lower, upper);
}


static inline double
interpolate_linear (double from, double to, double fraction)
{
	return from + (fraction * (to - from));
}

static inline double
interpolate_logarithmic (double from, double to, double fraction, double lower, double upper)
{
	// this is expensive -- optimize
	double l0 = logscale_to_position (from, lower, upper);
	double l1 = logscale_to_position (to, lower, upper);
	return position_to_logscale (l0 + fraction * (l1 - l0), lower, upper);
}

static inline double
interpolate_gain (double from, double to, double fraction, double upper)
{
	// this is expensive -- optimize
	double g0 = gain_to_position (from * 2. / upper);
	double g1 = gain_to_position (to * 2. / upper);
	return position_to_gain (g0 + fraction * (g1 - g0)) * upper / 2.;
}

#endif