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cx_g726_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
 */
 
#ifndef HIDE_SOURCE_STRINGS
static const char cvsid[] = 
      "$Id: cx_g726_16.c,v 1.2 2000/01/27 17:11:33 ucacoxh Exp $";
#endif /* HIDE_SOURCE_STRINGS */
/* 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.
 */
#define _PRIVATE_G726_
#include "cx_g726.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
g726_16_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_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
g726_16_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 &= 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);

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

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