src/G72x/g723_16.c

/*
 * 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.
 *
 * Sun Microsystems, Inc.
 * 2550 Garcia Avenue
 * Mountain View, California  94043
 */
/* 16kbps version created, used 24kbps code and changing as little as possible.
 * G.726 specs are available from ITU's gopher or WWW site (http://www.itu.ch)
 * If any errors are found, please contact me at mrand@tamu.edu
 *      -Marc Randolph
 */

/*
 * g723_16.c
 *
 * Description:
 *
 * g723_16_encoder (), g723_16_decoder ()
 *
 * These routines comprise an implementation of the CCITT G.726 16 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.
 *
 */

#include "g72x.h"
#include "g72x_priv.h"

/*
 * Maps G.723_16 code word to reconstructed scale factor normalized log
 * magnitude values.  Comes from Table 11/G.726
 */
static short _dqlntab [4] = { 116, 365, 365, 116 } ;

/* Maps G.723_16 code word to log of scale factor multiplier.
 *
 * _witab [4] is actually {-22 , 439, 439, -22}, but FILTD wants it
 * as WI << 5  (multiplied by 32), so we'll do that here
 */
static short _witab [4] = { -704, 14048, 14048, -704 } ;

/*
 * Maps G.723_16 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.
 */

/* Comes from FUNCTF */
static short _fitab [4] = { 0, 0xE00, 0xE00, 0 } ;

/* Comes from quantizer decision level tables (Table 7/G.726)
 */
static short qtab_723_16 [1] = { 261 } ;


/*
 * g723_16_encoder ()
 *
 * Encodes a linear PCM, A-law or u-law input sample and returns its 2-bit code.
 * Returns -1 if invalid input coding value.
 */
int
g723_16_encoder (
	int			sl,
	G72x_STATE *state_ptr)
{
	short sei, sezi, se, sez ;	/* ACCUM */
	short d ;					/* SUBTA */
	short y ;					/* MIX */
	short sr ;					/* ADDB */
	short dqsez ;				/* ADDC */
	short dq, i ;

	/* linearize input sample to 14-bit PCM */
	sl >>= 2 ;	/* sl of 14-bit dynamic range */

	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_723_16, 1) ;	/* i = ADPCM code */

	/* Since quantize () only produces a three level output
	 * (1, 2, or 3), we must create the fourth one on our own
	 */
	if (i == 3)					/* i code for the zero region */
		if ((d & 0x8000) == 0)	/* If d > 0, i=3 isn't right... */
			i = 0 ;

	dq = reconstruct (i & 2, _dqlntab [i], y) ; /* quantized diff. */

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

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

	update (2, y, _witab [i], _fitab [i], dq, sr, dqsez, state_ptr) ;

	return i ;
}

/*
 * g723_16_decoder ()
 *
 * Decodes a 2-bit CCITT G.723_16 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
g723_16_decoder (
	int			i,
	G72x_STATE *state_ptr)
{
	short sezi, sei, sez, se ;	/* ACCUM */
	short y ;					/* MIX */
	short sr ;					/* ADDB */
	short dq ;
	short dqsez ;

	i &= 0x03 ;			/* 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 & 0x02, _dqlntab [i], y) ; /* unquantize pred diff */

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

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

	update (2, y, _witab [i], _fitab [i], dq, sr, dqsez, state_ptr) ;

	/* sr was of 14-bit dynamic range */
	return (sr << 2) ;
}