--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/enc_lag6.c	Wed Apr 03 05:31:37 2024 +0000
@@ -0,0 +1,97 @@
+/*************************************************************************
+ *
+ *   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.
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+Word16 Enc_lag6 (      /* output: Return index of encoding     */
+    Word16 T0,         /* input : Pitch delay                  */
+    Word16 *T0_frac,   /* in/out: Fractional pitch delay       */
+    Word16 *T0_min,    /* in/out: Minimum search delay         */
+    Word16 *T0_max,    /* in/out: Maximum search delay         */
+    Word16 pit_min,    /* input : Minimum pitch delay          */
+    Word16 pit_max,    /* input : Maximum pitch delay          */
+    Word16 pit_flag    /* input : Flag for 1st or 3rd subframe */
+)
+{
+    Word16 index, i;
+
+    test (); 
+    if (pit_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
+        {   /* set fraction to 0 for delays > 94 */
+            *T0_frac = 0;       move16 (); 
+            index = add (T0, 368);
+        }
+
+        /* find T0_min and T0_max for second (or fourth) subframe */
+
+        *T0_min = sub (T0, 5);  move16 (); 
+        test (); 
+        if (sub (*T0_min, pit_min) < 0)
+        {
+            *T0_min = pit_min;  move16 (); 
+        }
+        *T0_max = add (*T0_min, 9);
+        test (); 
+        if (sub (*T0_max, pit_max) > 0)
+        {
+            *T0_max = pit_max;  move16 (); 
+            *T0_min = sub (*T0_max, 9); move16 (); 
+        }
+    } 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;
+}