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 */

/*

 * g721.c

 *

 * Description:

 *

 * g721_encoder (), g721_decoder ()

 *

 * These routines comprise an implementation of the CCITT G.721 ADPCM

 * coding algorithm.  Essentially, this implementation is identical to

 * the bit level description except for a few deviations which

 * take advantage of work station attributes, such as hardware 2's

 * complement arithmetic and large memory.  Specifically, certain time

 * consuming operations such as multiplications are replaced

 * with lookup tables and software 2's complement operations are

 * replaced with hardware 2's complement.

 *

 * The deviation from the bit level specification (lookup tables)

 * preserves the bit level performance specifications.

 *

 * As outlined in the G.721 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 "g72x.h"

#include "g72x_priv.h"

static short qtab_721 [7] = { -124, 80, 178, 246, 300, 349, 400 } ;

/*

 * Maps G.721 code word to reconstructed scale factor normalized log

 * magnitude values.

 */

static short _dqlntab [16] = { -2048, 4, 135, 213, 273, 323, 373, 425,

              425, 373, 323, 273, 213, 135, 4, -2048 } ;

/* Maps G.721 code word to log of scale factor multiplier. */

static short _witab [16] = { -12, 18, 41, 64, 112, 198, 355, 1122,

              1122, 355, 198, 112, 64, 41, 18, -12 } ;

/*

 * Maps G.721 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 [16] = { 0, 0, 0, 0x200, 0x200, 0x200, 0x600, 0xE00,

              0xE00, 0x600, 0x200, 0x200, 0x200, 0, 0, 0 } ;

/*

 * g721_encoder ()

 *

 * Encodes the input vale of linear PCM, A-law or u-law data sl and returns

 * the resulting code. -1 is returned for unknown input coding value.

 */

int

g721_encoder (

  int   sl,

  G72x_STATE *state_ptr)

{

  short   sezi, se, sez ;   /* ACCUM */

  short   d ;     /* SUBTA */

  short   sr ;      /* ADDB */

  short   y ;     /* MIX */

  short   dqsez ;     /* ADDC */

  short   dq, i ;

  /* linearize input sample to 14-bit PCM */

  sl >>= 2 ;      /* 14-bit dynamic range */

  sezi = predictor_zero (state_ptr) ;

  sez = sezi >> 1 ;

  se = (sezi + predictor_pole (state_ptr)) >> 1 ; /* estimated signal */

  d = sl - se ;       /* estimation difference */

  /* quantize the prediction difference */

  y = step_size (state_ptr) ;   /* quantizer step size */

  i = quantize (d, y, qtab_721, 7) ;  /* i = ADPCM code */

  dq = reconstruct (i & 8, _dqlntab [i], y) ; /* quantized est diff */

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

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

  update (4, y, arith_shift_left (_witab [i], 5), _fitab [i], dq, sr, dqsez, state_ptr) ;

  return i ;

}

/*

 * g721_decoder ()

 *

 * Description:

 *

 * Decodes a 4-bit code of G.721 encoded data of i and

 * returns the resulting linear PCM, A-law or u-law value.

 * return -1 for unknown out_coding value.

 */

int

g721_decoder (

  int   i,

  G72x_STATE *state_ptr)

{

  short   sezi, sei, sez, se ;  /* ACCUM */

  short   y ;     /* MIX */

  short   sr ;      /* ADDB */

  short   dq ;

  short   dqsez ;

  i &= 0x0f ;     /* 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) ; /* dynamic quantizer step size */

  dq = reconstruct (i & 0x08, _dqlntab [i], y) ; /* quantized diff. */

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

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

  update (4, y, arith_shift_left (_witab [i], 5), _fitab [i], dq, sr, dqsez, state_ptr) ;

  /* sr was 14-bit dynamic range */

  return arith_shift_left (sr, 2) ;

}