/*
 * This source code is a product of Sun Microsystems, Inc. and is provided
 * for unrestricted use.  Users may copy or modify this source code without
 * charge.
 *
 * SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
 * THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
 *
 * Sun source code is provided with no support and without any obligation on
 * the part of Sun Microsystems, Inc. to assist in its use, correction,
 * modification or enhancement.
 *
 * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
 * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE
 * OR ANY PART THEREOF.
 *
 * In no event will Sun Microsystems, Inc. be liable for any lost revenue
 * or profits or other special, indirect and consequential damages, even if
 * Sun has been advised of the possibility of such damages.
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 * Sun Microsystems, Inc.
 * 2550 Garcia Avenue
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 */
 
#ifndef HIDE_SOURCE_STRINGS
static const char cvsid[] = 
	"$Id: cx_g726_24.c,v 1.2 2000/01/27 17:11:33 ucacoxh Exp $";
#endif /* HIDE_SOURCE_STRINGS */

/*
 * g726_24.c
 *
 * Description:
 *
 * g726_24_encoder(), g726_24_decoder()
 *
 * These routines comprise an implementation of the CCITT G.726 24 Kbps
 * ADPCM coding algorithm.  Essentially, this implementation is identical to
 * the bit level description except for a few deviations which take advantage
 * of workstation attributes, such as hardware 2's complement arithmetic.
 */
#define _PRIVATE_G726_
#include "cx_g726.h"

/*
 * Maps G.726_24 code word to reconstructed scale factor normalized log
 * magnitude values.
 */
static short	_dqlntab[8] = {-2048, 135, 273, 373, 373, 273, 135, -2048};

/* Maps G.726_24 code word to log of scale factor multiplier. */
static short	_witab[8] = {-128, 960, 4384, 18624, 18624, 4384, 960, -128};

/*
 * Maps G.726_24 code words to a set of values whose long and short
 * term averages are computed and then compared to give an indication
 * how stationary (steady state) the signal is.
 */
static short	_fitab[8] = {0, 0x200, 0x400, 0xE00, 0xE00, 0x400, 0x200, 0};

static short qtab_726_24[3] = {8, 218, 331};

/*
 * g726_24_encoder()
 *
 * Encodes a linear PCM, A-law or u-law input sample and returns its 3-bit code.
 * Returns -1 if invalid input coding value.
 */
int
g726_24_encoder(
	int		sl,
	int		in_coding,
	struct g726_state *state_ptr)
{
	short		sei, sezi, se, sez;	/* ACCUM */
	short		d;			/* SUBTA */
	short		y;			/* MIX */
	short		sr;			/* ADDB */
	short		dqsez;			/* ADDC */
	short		dq, i;

	switch (in_coding) {	/* linearize input sample to 14-bit PCM */
	case AUDIO_ENCODING_LINEAR:
		sl >>= 2;		/* sl of 14-bit dynamic range */
		break;
	default:
		return (-1);
	}

	sezi = predictor_zero(state_ptr);
	sez = sezi >> 1;
	sei = sezi + predictor_pole(state_ptr);
	se = sei >> 1;			/* se = estimated signal */

	d = sl - se;			/* d = estimation diff. */

	/* quantize prediction difference d */
	y = step_size(state_ptr);	/* quantizer step size */
	i = quantize(d, y, qtab_726_24, 3);	/* i = ADPCM code */
	dq = reconstruct(i & 4, _dqlntab[i], y); /* quantized diff. */

	sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq; /* reconstructed signal */

	dqsez = sr + sez - se;		/* pole prediction diff. */

	update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

	return (i);
}

/*
 * g726_24_decoder()
 *
 * Decodes a 3-bit CCITT G.726_24 ADPCM code and returns
 * the resulting 16-bit linear PCM, A-law or u-law sample value.
 * -1 is returned if the output coding is unknown.
 */
int
g726_24_decoder(
	int		i,
	int		out_coding,
	struct g726_state *state_ptr)
{
	short		sezi, sei, sez, se;	/* ACCUM */
	short		y;			/* MIX */
	short		sr;			/* ADDB */
	short		dq;
	short		dqsez;

	i &= 0x07;			/* mask to get proper bits */
	sezi = predictor_zero(state_ptr);
	sez = sezi >> 1;
	sei = sezi + predictor_pole(state_ptr);
	se = sei >> 1;			/* se = estimated signal */

	y = step_size(state_ptr);	/* adaptive quantizer step size */
	dq = reconstruct(i & 0x04, _dqlntab[i], y); /* unquantize pred diff */

	sr = (dq < 0) ? (se - (dq & 0x3FFF)) : (se + dq); /* reconst. signal */

	dqsez = sr - se + sez;			/* pole prediction diff. */

	update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

	switch (out_coding) {
	case AUDIO_ENCODING_LINEAR:
		return (sr << 2);	/* sr was of 14-bit dynamic range */
	default:
		return (-1);
	}
}
