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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_tau(FLT y1, FLT y2, FLT y3)
{
	return ((y1 - y3)/(2.0*(y3 + y1 - (2.0*y2))));
}

FLT yin(LingotCore* core) {
	FLT dt_tau;
	FLT dt_tau_sum = 0;
	FLT dpt_right = 1.0/0.0, dpt_center, dpt_left;
	FLT thr = core->conf->yin_threshold;
	FLT dpt_min = 1.0/0.0;
	FLT dpt_min_left, dpt_min_right;
	int j, tau, tau_min;
	int len = core->conf->temporal_buffer_size / 2;

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

		dpt_left = dpt_center;
		dpt_center = dpt_right;
		dpt_right = dt_tau / ( 1.0 / tau * dt_tau_sum );

		if (dpt_center < dpt_min)
		{
			dpt_min_left = dpt_left;
			dpt_min = dpt_center;
			dpt_min_right = dpt_right;
			tau_min = tau - 1;
		}
	}
	return (FLT)tau_min + yin_interpolate_tau(dpt_left, dpt_center, dpt_right);
}