dec_lag3.c

C源程序---G.729a语音代码G.729a语音代码

/*
   ITU-T G.729A Speech Coder    ANSI-C Source Code
   Version 1.1    Last modified: September 1996

   Copyright (c) 1996,
   AT&T, France Telecom, NTT, Universite de Sherbrooke
   All rights reserved.
*/

/*------------------------------------------------------------------------*
 *    Function Dec_lag3                                                   *
 *             ~~~~~~~~                                                   *
 *   Decoding of fractional pitch lag with 1/3 resolution.                *
 * See "Enc_lag3.c" for more details about the encoding procedure.        *
 *------------------------------------------------------------------------*/

#include "typedef.h"
#include "basic_op.h"
#include "ld8a.h"

void Dec_lag3(
  Word16 index,       /* input : received pitch index           */
  Word16 pit_min,     /* input : minimum pitch lag              */
  Word16 pit_max,     /* input : maximum pitch lag              */
  Word16 i_subfr,     /* input : subframe flag                  */
  Word16 *T0,         /* output: integer part of pitch lag      */
  Word16 *T0_frac     /* output: fractional part of pitch lag   */
)
{
  Word16 i;
  Word16 T0_min, T0_max;

  if (i_subfr == 0)                  /* if 1st subframe */
  {
    if (sub(index, 197) < 0)
    {
      /* *T0 = (index+2)/3 + 19 */

      *T0 = add(mult(add(index, 2), 10923), 19);

      /* *T0_frac = index - *T0*3 + 58 */

      i = add(add(*T0, *T0), *T0);
      *T0_frac = add(sub(index, i), 58);
    }
    else
    {
      *T0 = sub(index, 112);
      *T0_frac = 0;
    }

  }

  else  /* second subframe */
  {
    /* find T0_min and T0_max for 2nd subframe */

    T0_min = sub(*T0, 5);
    if (sub(T0_min, pit_min) < 0)
    {
      T0_min = pit_min;
    }

    T0_max = add(T0_min, 9);
    if (sub(T0_max, pit_max) > 0)
    {
      T0_max = pit_max;
      T0_min = sub(T0_max, 9);
    }

    /* i = (index+2)/3 - 1 */
    /* *T0 = i + t0_min;    */

    i = sub(mult(add(index, 2), 10923), 1);
    *T0 = add(i, T0_min);

    /* t0_frac = index - 2 - i*3; */

    i = add(add(i, i), i);
    *T0_frac = sub(sub(index, 2), i);
  }

  return;
}