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g723_40.cpp

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/*
 * g723_40.c
 *
 * Description:
 *
 * g723_40_encoder(), g723_40_decoder()
 *
 * These routines comprise an implementation of the CCITT G.723 40Kbps
 * 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.
 *
 * The deviation from the bit level specification (lookup tables),
 * preserves the bit level performance specifications.
 *
 * As outlined in the G.723 Recommendation, the algorithm is broken
 * down into modules.  Each section of code below is preceded by
 * the name of the module which it is implementing.
 *
 */
#include "wx/wxprec.h"
#include "wx/mmedia/internal/g72x.h"

/*
 * Maps G.723_40 code word to ructeconstructed scale factor normalized log
 * magnitude values.
 */
static short      _dqlntab[32] = {-2048, -66, 28, 104, 169, 224, 274, 318,
                        358, 395, 429, 459, 488, 514, 539, 566,
                        566, 539, 514, 488, 459, 429, 395, 358,
                        318, 274, 224, 169, 104, 28, -66, -2048};

/* Maps G.723_40 code word to log of scale factor multiplier. */
static short      _witab[32] = {448, 448, 768, 1248, 1280, 1312, 1856, 3200,
                  4512, 5728, 7008, 8960, 11456, 14080, 16928, 22272,
                  22272, 16928, 14080, 11456, 8960, 7008, 5728, 4512,
                  3200, 1856, 1312, 1280, 1248, 768, 448, 448};

/*
 * Maps G.723_40 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[32] = {0, 0, 0, 0, 0, 0x200, 0x200, 0x200,
                  0x200, 0x200, 0x400, 0x600, 0x800, 0xA00, 0xC00, 0xC00,
                  0xC00, 0xC00, 0xA00, 0x800, 0x600, 0x400, 0x200, 0x200,
                  0x200, 0x200, 0x200, 0, 0, 0, 0, 0};

static short qtab_723_40[15] = {-122, -16, 68, 139, 198, 250, 298, 339,
                        378, 413, 445, 475, 502, 528, 553};

/*
 * g723_40_encoder()
 *
 * Encodes a 16-bit linear PCM, A-law or u-law input sample and retuens
 * the resulting 5-bit CCITT G.723 40Kbps code.
 * Returns -1 if the input coding value is invalid.
 */
int
g723_40_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 difference */

      /* quantize prediction difference */
      y = step_size(state_ptr);     /* adaptive quantizer step size */
      i = quantize(d, y, qtab_723_40, 15);      /* i = ADPCM code */

      dq = reconstruct(i & 0x10, _dqlntab[i], y);     /* quantized diff */

      sr = (dq < 0) ? se - (dq & 0x7FFF) : se + dq; /* reconstructed signal */

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

      update(5, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

      return (i);
}

/*
 * g723_40_decoder()
 *
 * Decodes a 5-bit CCITT G.723 40Kbps 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_40_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 &= 0x1f;              /* 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 & 0x10, _dqlntab[i], y);     /* estimation diff. */

      sr = (dq < 0) ? (se - (dq & 0x7FFF)) : (se + dq); /* reconst. signal */

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

      update(5, 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, 0x10, qtab_723_40));
      case AUDIO_ENCODING_ULAW:
            return (tandem_adjust_ulaw(sr, se, y, i, 0x10, qtab_723_40));
      case AUDIO_ENCODING_LINEAR:
            return (sr << 2); /* sr was of 14-bit dynamic range */
      default:
            return (-1);
      }
}

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