/* LPC_and_Cepstrumc.cpp
 *
 * Copyright (C) 1994-2018 David Weenink
 *
 * This code 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 code 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 work. If not, see <http://www.gnu.org/licenses/>.
 */

/*
 djmw 20020812 GPL header
 djmw 20080122 float -> double
*/

#include "LPC_and_Cepstrumc.h"

void LPC_Frame_into_Cepstrumc_Frame (LPC_Frame me, Cepstrumc_Frame thee) {
	integer n = my nCoefficients > thy nCoefficients ? thy nCoefficients : my nCoefficients;
	double *c = thy c, *a = my a.at;

	c [0] = 0.5 * log (my gain);
	if (n == 0) {
		return;
	}

	c [1] = -a [1];
	for (integer i = 2; i <= n; i ++) {
		c [i] = 0;
		for (integer k = 1; k < i; k ++) {
			c [i] += a [i - k] * c [k] * k;
		}
		c [i] = -a [i] - c [i] / i;
	}
}

void Cepstrumc_Frame_into_LPC_Frame (Cepstrumc_Frame me, LPC_Frame thee) {
	double *c = my c, *a = thy a.at;
	thy gain = exp (2.0 * c [0]);
	if (thy nCoefficients == 0) {
		return;
	}
	a [1] = -c [1];
	for (integer i = 2; i <= thy nCoefficients; i ++) {
		c [i] *= i;
	}
	for (integer i = 2; i <= thy nCoefficients; i ++) {
		a [i] = c [i];
		for (integer j = 1 ; j < i; j++) {
			a [i] += a [j] * c [i - j];
		}
		a [i] /= -i;
	}
	for (integer i = 2; i <= thy nCoefficients; i ++) {
		c [i] /= i;
	}
}

autoCepstrumc LPC_to_Cepstrumc (LPC me) {
	try {
		autoCepstrumc thee = Cepstrumc_create (my xmin, my xmax, my nx, my dx, my x1,  my maxnCoefficients, 1.0 / my samplingPeriod);

		for (integer i = 1; i <= my nx; i ++) {
			Cepstrumc_Frame_init (& thy frame [i], my d_frames [i].nCoefficients);
			LPC_Frame_into_Cepstrumc_Frame (& my d_frames [i], & thy frame [i]);
		}
		return thee;
	} catch (MelderError) {
		Melder_throw (me, U": no Cepstrum created.");
	}
}

autoLPC Cepstrumc_to_LPC (Cepstrumc me) {
	try {
		autoLPC thee = LPC_create (my xmin, my xmax, my nx, my dx, my x1,
		                           my maxnCoefficients, 1.0 / my samplingFrequency);
		for (integer i = 1; i <= my nx; i ++) {
			LPC_Frame_init (& thy d_frames [i], my frame [i].nCoefficients);
			Cepstrumc_Frame_into_LPC_Frame (& my frame [i], & thy d_frames [i]);
		}
		return thee;
	} catch (MelderError) {
		Melder_throw (me, U":no LPC created.");
	}
}

/* End of file LPC_and_Cepstrumc.cpp  */
