RTL271_1/amrnb/enc_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             : enc_lag3.c
*      Purpose          : Encoding of fractional pitch lag with 1/3 resolution.
*
********************************************************************************
*/
/*
********************************************************************************
*                         MODULE INCLUDE FILE AND VERSION ID
********************************************************************************
*/
#include "enc_lag3.h"
const char enc_lag3_id[] = "@(#)$Id $" enc_lag3_h;
 
/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"
#include "basic_op.h"
#include "count.h"
#include "cnst.h"

/*
********************************************************************************
*                         PUBLIC PROGRAM CODE
********************************************************************************
*/
/*************************************************************************
 *
 *   FUNCTION:  Enc_lag3
 *
 *   PURPOSE:  Encoding of fractional pitch lag with 1/3 resolution.
 *
 *   DESCRIPTION:
 *                    First and third subframes:
 *                    --------------------------
 *   The pitch range is divided as follows:
 *           19 1/3  to   84 2/3   resolution 1/3
 *           85      to   143      resolution 1
 *
 *   The period is encoded with 8 bits.
 *   For the range with fractions:
 *     index = (T-19)*3 + frac - 1;
 *                         where T=[19..85] and frac=[-1,0,1]
 *   and for the integer only range
 *     index = (T - 85) + 197;        where T=[86..143]
 *
 *                    Second and fourth subframes:
 *                    ----------------------------
 *   For the 2nd and 4th subframes a resolution of 1/3 is always used,
 *   and the search range is relative to the lag in previous subframe.
 *   If t0 is the lag in the previous subframe then
 *   t_min=t0-5   and  t_max=t0+4   and  the range is given by
 *        t_min - 2/3   to  t_max + 2/3
 *
 *   The period in the 2nd (and 4th) subframe is encoded with 5 bits:
 *     index = (T-(t_min-1))*3 + frac - 1;
 *                 where T=[t_min-1..t_max+1]
 *
 *************************************************************************/
Word16
Enc_lag3(                /* o  : Return index of encoding             */
    Word16 T0,           /* i  : Pitch delay                          */
    Word16 T0_frac,      /* i  : Fractional pitch delay               */
    Word16 T0_prev,      /* i  : Integer pitch delay of last subframe */
    Word16 T0_min,       /* i  : minimum of search range              */
    Word16 T0_max,       /* i  : maximum of search range              */
    Word16 delta_flag,   /* i  : Flag for 1st (or 3rd) subframe       */
    Word16 flag4         /* i  : Flag for encoding with 4 bits        */
    )
{
   Word16 index, i, tmp_ind, uplag;
   Word16 tmp_lag;
   
   test (); 
   if (delta_flag == 0)
   {  /* if 1st or 3rd subframe */

      /* encode pitch delay (with fraction) */
      
      test (); 
      if (sub_ex (T0, 85) <= 0)
      {
         /* index = T0*3 - 58 + T0_frac   */
         i = add_ex (add_ex (T0, T0), T0);
         index = add_ex (sub_ex (i, 58), T0_frac);
      }
      else
      {
         index = add_ex (T0, 112);
      }
   }
   else
   {   /* if second or fourth subframe */
      test (); 
      if (flag4 == 0) {
         
         /* 'normal' encoding: either with 5 or 6 bit resolution */
		  
         /* index = 3*(T0 - T0_min) + 2 + T0_frac */
         i = sub_ex (T0, T0_min);
         i = add_ex (add_ex (i, i), i);
         index = add_ex (add_ex (i, 2), T0_frac);
      }
      else {
         
         /* encoding 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);
         
         uplag = add_ex (add_ex (add_ex (T0, T0), T0), T0_frac);
         
         i = sub_ex (tmp_lag, 2);
         tmp_ind = add_ex (add_ex (i, i), i);
         
         test ();
         if (sub_ex (tmp_ind, uplag) >= 0) { 
            index = add_ex (sub_ex (T0, tmp_lag), 5);
         } 
         else {
            
            i = add_ex (tmp_lag, 1);
            i = add_ex (add_ex (i, i), i);
            
            test ();
            if (sub_ex (i, uplag) > 0) {
               
                index = add_ex ( sub_ex (uplag, tmp_ind), 3);                
            }
            else {
               
               index = add_ex (sub_ex (T0, tmp_lag), 11);
            }
         }
         
      } /* end if (encoding with 4 bit resolution) */
   }   /* end if (second of fourth subframe) */
   
   return index;
}