+
−/*
+
−********************************************************************************
+
−*
+
−*      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_lag6.c
+
−*      Purpose          : Encoding of fractional pitch lag with 1/6 resolution.
+
−*
+
−********************************************************************************
+
−*/
+
−/*
+
−********************************************************************************
+
−*                         MODULE INCLUDE FILE AND VERSION ID
+
−********************************************************************************
+
−*/
+
−#include "namespace.h"
+
−#include "enc_lag6.h"
+
− 
+
−/*
+
−********************************************************************************
+
−*                         INCLUDE FILES
+
−********************************************************************************
+
−*/
+
−#include "typedef.h"
+
−#include "basic_op.h"
+
−#include "no_count.h"
+
− 
+
−/*
+
−********************************************************************************
+
−*                         LOCAL VARIABLES AND TABLES
+
−********************************************************************************
+
−*/
+
− 
+
−/*
+
−********************************************************************************
+
−*                         PUBLIC PROGRAM CODE
+
−********************************************************************************
+
−*/
+
−/*************************************************************************
+
− *
+
− *   FUNCTION:  Enc_lag6
+
− *
+
− *   PURPOSE:  Encoding of fractional pitch lag with 1/6 resolution.
+
− *
+
− *   DESCRIPTION:
+
− *                    First and third subframes:
+
− *                    --------------------------
+
− *   The pitch range is divided as follows:
+
− *           17 3/6  to   94 3/6   resolution 1/6
+
− *           95      to   143      resolution 1
+
− *
+
− *   The period is encoded with 9 bits.
+
− *   For the range with fractions:
+
− *     index = (T-17)*6 + frac - 3;
+
− *                         where T=[17..94] and frac=[-2,-1,0,1,2,3]
+
− *   and for the integer only range
+
− *     index = (T - 95) + 463;        where T=[95..143]
+
− *
+
− *                    Second and fourth subframes:
+
− *                    ----------------------------
+
− *   For the 2nd and 4th subframes a resolution of 1/6 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-1) 3/6   to  (t_max) 3/6
+
− *
+
− *   The period in the 2nd (and 4th) subframe is encoded with 6 bits:
+
− *     index = (T-(t_min-1))*6 + frac - 3;
+
− *                 where T=[t_min-1..t_max] and frac=[-2,-1,0,1,2,3]
+
− *
+
− *   Note that only 61 values are used. If the decoder receives 61, 62,
+
− *   or 63 as the relative pitch index, it means that a transmission
+
− *   error occurred and the pitch from previous subframe should be used.
+
− *
+
− *************************************************************************/
+
−Word16 Enc_lag6 (        /* o : Return index of encoding             */
+
−    Word16 T0,           /* i : Pitch delay                          */
+
−    Word16 T0_frac,      /* i : Fractional pitch delay               */
+
−    Word16 T0_min,       /* i : minimum of search range              */
+
−    Word16 delta_flag    /* i : Flag for 1st (or 3rd) subframe       */
+
−)
+
−{
+
−    Word16 index, i;
+
−
+
−    test (); 
+
−    if (delta_flag == 0)          /* if 1st or 3rd subframe */
+
−    {
+
−       /* encode pitch delay (with fraction) */
+
−       test (); 
+
−       if (sub (T0, 94) <= 0)
+
−       {
+
−          /* index = T0*6 - 105 + T0_frac */
+
−          i = add (add (T0, T0), T0);
+
−          index = add (sub (add (i, i), 105), T0_frac);
+
−       }
+
−       else
+
−       {
+
−          index = add (T0, 368);
+
−       }
+
−       
+
−    }
+
−    else
+
−       /* if second or fourth subframe */
+
−    {
+
−       /* index = 6*(T0-T0_min) + 3 + T0_frac  */
+
−       i = sub (T0, T0_min);
+
−       i = add (add (i, i), i);
+
−       index = add (add (add (i, i), 3), T0_frac);
+
−    }
+
−    
+
−    return index;
+
−}