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g723_24.cpp

/*
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 * OR ANY PART THEREOF.
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 * or profits or other special, indirect and consequential damages, even if
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 * 2550 Garcia Avenue
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 */

/*
 * g723_24.c
 *
 * Description:
 *
 * g723_24_encoder(), g723_24_decoder()
 *
 * These routines comprise an implementation of the CCITT G.723 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.
 *
 */
#include "wx/wxprec.h"
#include "wx/mmedia/internal/g72x.h"

/*
 * Maps G.723_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.723_24 code word to log of scale factor multiplier. */
static short      _witab[8] = {-128, 960, 4384, 18624, 18624, 4384, 960, -128};

/*
 * Maps G.723_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_723_24[3] = {8, 218, 331};

/*
 * g723_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
g723_24_encoder(
      int         sl,
      int         in_coding,
      struct 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;

      switch (in_coding) {    /* linearize input sample to 14-bit PCM */
      case AUDIO_ENCODING_ALAW:
            sl = alaw2linear(sl) >> 2;
            break;
      case AUDIO_ENCODING_ULAW:
            sl = ulaw2linear(sl) >> 2;
            break;
      case AUDIO_ENCODING_LINEAR:
            sl = ((short)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_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);
}

/*
 * g723_24_decoder()
 *
 * Decodes a 3-bit CCITT G.723_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
g723_24_decoder(
      int         i,
      int         out_coding,
      struct g72x_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_ALAW:
            return (tandem_adjust_alaw(sr, se, y, i, 4, qtab_723_24));
      case AUDIO_ENCODING_ULAW:
            return (tandem_adjust_ulaw(sr, se, y, i, 4, qtab_723_24));
      case AUDIO_ENCODING_LINEAR:
            return (sr << 2); /* sr was of 14-bit dynamic range */
      default:
            return (-1);
      }
}

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