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//-*- C++ -*-
/*
 * YIN pitch estimator
 * Copyright (C) 2008 Piotr Pawlow <pp@siedziba.pl>
 *
 * This file is part of lingot.
 *
 * lingot 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.
 *
 * lingot 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 lingot; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/* Implementation of YIN algorithm, published in:
 *
 * A. de Cheveigne and H. Kawahara: YIN, an F0 estimator
 * J. Acoust. Soc. Am., Vol. 111, No. 4, April 2002
 * http://www.ircam.fr/pcm/cheveign/pss/2002_JASA_YIN.pdf
 */

#include "lingot-yin.h"

inline FLT yin_sqr(FLT x)
{
	return x*x;
}

inline FLT yin_interpolate_x(FLT y1, FLT y2, FLT y3)
{
	if ((y1 == y2) && (y2 == y3)) return 0;
	return ((y1 - y3)/(2.0*(y3 + y1 - (2.0*y2))));
}

inline FLT yin_interpolate_y(FLT y1, FLT y2, FLT y3)
{
	if ((y1 == y2) && (y2 == y3)) return y1;
	return (((6.0 * y2) - y1 + (3.0 * y3) - (4.0 * yin_sqr(y2 - y3) / (y3 - (2.0 * y2) + y1))) / 8.0);
}

void yin(LingotCore* core) {
	FLT dt_tau[3];
	FLT dt_tau_sum = 0;
	FLT dpt[3];
	FLT thr_low = core->conf->yin_threshold_low;
	FLT thr_high = core->conf->yin_threshold_high;
	FLT dpt_min = 1.0/0.0;
	FLT dpt_interpolated;
	FLT tau_min;
	int j, tau;
	int len = core->conf->temporal_buffer_size / 2;

	for (tau = 1; tau < len; tau++)
	{
		dt_tau[0] = dt_tau[1];
		dt_tau[1] = dt_tau[2];
		dt_tau[2] = 0;
		for (j = 0; j < len ; j++)
		{
			dt_tau[2] += yin_sqr(core->temporal_buffer[j] - core->temporal_buffer[j+tau]);
		}
		dt_tau_sum += dt_tau[2];

		dpt[0] = dpt[1];
		dpt[1] = dpt[2];
		dpt[2] = dt_tau[2] / ( 1.0 / tau * dt_tau_sum );

		if (tau >= 3)
		{
			if ((dpt[1] <= dpt[0]) && (dpt[1] <= dpt[2]))
			{
// we have local minimum
				dpt_interpolated = yin_interpolate_y(dpt[0], dpt[1], dpt[2]);
				if (dpt_interpolated < dpt_min)
				{
					dpt_min = dpt_interpolated;
					tau_min = (FLT)tau - 1 + yin_interpolate_x(dt_tau[0], dt_tau[1], dt_tau[2]);
					if (dpt_min < thr_low) break;
				}
			}
		}
	}
	if ((tau_min > 1) && (dpt_min < thr_high)) core->freq = core->conf->sample_rate / (FLT)core->conf->oversampling / tau_min; else core->freq = 0;
}