RTL271_1/amrnb/dec_lag3.c

/*
********************************************************************************
*
*      GSM AMR-NB speech codec   R98   Version 7.6.0   December 12, 2001
*                                R99   Version 3.3.0                
*                                REL-4 Version 4.1.0                
*
********************************************************************************
*
*      File             : dec_lag3.c
*      Purpose          : Decoding of fractional pitch lag with 1/3 resolution.
*                         Extract the integer and fraction parts of the pitch lag from
*                         the received adaptive codebook index.
*
********************************************************************************
*/

/*
********************************************************************************
*                         MODULE INCLUDE FILE AND VERSION ID
********************************************************************************
*/
#include "dec_lag3.h"
const char dec_lag3_id[] = "@(#)$Id $" dec_lag3_h;

 
/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"
#include "basic_op.h"
#include "count.h"

/*
********************************************************************************
*                         LOCAL VARIABLES AND TABLES
********************************************************************************
*/

/*
********************************************************************************
*                         PUBLIC PROGRAM CODE
********************************************************************************
*/
/*************************************************************************
 *   FUNCTION:   Dec_lag3
 *
 *   PURPOSE:  Decoding of fractional pitch lag with 1/3 resolution.
 *             Extract the integer and fraction parts of the pitch lag from
 *             the received adaptive codebook index.
 *
 *    See "Enc_lag3.c" for more details about the encoding procedure.
 *
 *    The fractional lag in 1st and 3rd subframes is encoded with 8 bits
 *    while that in 2nd and 4th subframes is relatively encoded with 4, 5
 *    and 6 bits depending on the mode.
 *
 *************************************************************************/
void Dec_lag3(Word16 index,     /* i : received pitch index                 */
              Word16 t0_min,    /* i : minimum of search range              */
              Word16 t0_max,    /* i : maximum of search range              */
              Word16 i_subfr,   /* i : subframe flag                        */
              Word16 T0_prev,   /* i : integer pitch delay of last subframe
                                       used in 2nd and 4th subframes        */
              Word16 * T0,      /* o : integer part of pitch lag            */ 
              Word16 * T0_frac, /* o : fractional part of pitch lag         */
              Word16 flag4      /* i : flag for encoding with 4 bits        */
              )
{
    Word16 i;
    Word16 tmp_lag;
    
    test (); 
    if (i_subfr == 0) {    /* if 1st or 3rd subframe */
       test ();
	   if (sub_ex(index, 197) < 0) {
          
          *T0 = add_ex(mult_ex(add_ex(index, 2), 10923), 19);
           
          i = add_ex(add_ex(*T0, *T0), *T0);
          *T0_frac = add_ex(sub_ex(index, i), 58);
       } else {
          *T0 = sub_ex(index, 112);
          *T0_frac = 0;                                        move16 ();
       }
       
    } else {    /* 2nd or 4th subframe */

       test ();
       if (flag4 == 0) {
          
          /* 'normal' decoding: either with 5 or 6 bit resolution */
          
          i = sub_ex(mult_ex(add_ex(index, 2), 10923), 1);
          *T0 = add_ex(i, t0_min);
          
          i = add_ex(add_ex(i, i), i);
          *T0_frac = sub_ex(sub_ex(index, 2), i);
       }
       else {
          
          /* decoding with 4 bit resolution */
          
          tmp_lag = T0_prev;                                   move16 ();

          test ();
          if ( sub_ex( sub_ex(tmp_lag, t0_min), 5) > 0)
             tmp_lag = add_ex (t0_min, 5);
          test ();
          if ( sub_ex( sub_ex(t0_max, tmp_lag), 4) > 0)
             tmp_lag = sub_ex (t0_max, 4);
          
          test ();          
          if (sub_ex(index, 4) < 0)
          {
             i = sub_ex(tmp_lag, 5);
             *T0 = add_ex(i, index);
             *T0_frac = 0;                                     move16 ();
          }
          else
          {
             test ();
             if (sub_ex(index, 12) < 0)
             {
                i = sub_ex(mult_ex(sub_ex(index, 5), 10923), 1);
                *T0 = add_ex(i, tmp_lag);
                
                i = add_ex(add_ex(i, i), i);
                *T0_frac = sub_ex(sub_ex(index, 9), i);
             }
             else
             {
                i = add_ex( sub_ex (index, 12), tmp_lag);
                *T0 = add_ex (i, 1);                
                *T0_frac = 0;                                  move16 ();
             }
          }
          
       } /* end if (decoding with 4 bit resolution) */
    }
    
    return;
}