--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/enc_lag6.c	Mon May 06 02:46:19 2024 +0000
@@ -0,0 +1,116 @@
+/*
+********************************************************************************
+*
+*      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;
+}