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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 "g72x.h"

#include "g72x_priv.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,

  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_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,

  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) ;

  return arith_shift_left (sr, 2) ; /* sr was of 14-bit dynamic range */

}