--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/dec_lag6.c	Wed Apr 03 05:31:37 2024 +0000
@@ -0,0 +1,118 @@
+/*************************************************************************
+ *   FUNCTION:   Dec_lag6
+ *
+ *   PURPOSE:  Decoding of fractional pitch lag with 1/6 resolution.
+ *             Extract the integer and fraction parts of the pitch lag from
+ *             the received adaptive codebook index.
+ *
+ *    See "Enc_lag6.c" for more details about the encoding procedure.
+ *
+ *    The fractional lag in 1st and 3rd subframes is encoded with 9 bits
+ *    while that in 2nd and 4th subframes is relatively encoded with 6 bits.
+ *    Note that in relative encoding 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. In this case, the pitch lag from
+ *    previous subframe is used.
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+/* Old integer lag */
+
+Word16 old_T0;
+
+Word16 
+Dec_lag6 (             /* output: return integer pitch lag       */
+    Word16 index,      /* input : received pitch index           */
+    Word16 pit_min,    /* input : minimum pitch lag              */
+    Word16 pit_max,    /* input : maximum pitch lag              */
+    Word16 i_subfr,    /* input : subframe flag                  */
+    Word16 L_frame_by2,/* input : speech frame size divided by 2 */
+    Word16 *T0_frac,   /* output: fractional part of pitch lag   */
+    Word16 bfi         /* input : bad frame indicator            */
+)
+{
+    Word16 pit_flag;
+    Word16 T0, i;
+    static Word16 T0_min, T0_max;
+
+    pit_flag = i_subfr;         move16 (); /* flag for 1st or 3rd subframe */
+    test (); 
+    if (sub (i_subfr, L_frame_by2) == 0)
+    {
+        pit_flag = 0;           move16 (); 
+    }
+    test (); 
+    if (pit_flag == 0)          /* if 1st or 3rd subframe */
+    {
+        test (); 
+        if (bfi == 0)
+        {                       /* if bfi == 0 decode pitch */
+            test (); 
+            if (sub (index, 463) < 0)
+            {
+                /* T0 = (index+5)/6 + 17 */
+                T0 = add (mult (add (index, 5), 5462), 17);
+                i = add (add (T0, T0), T0);
+                /* *T0_frac = index - T0*6 + 105 */
+                *T0_frac = add (sub (index, add (i, i)), 105);
+                                move16 (); 
+            }
+            else
+            {
+                T0 = sub (index, 368);
+                *T0_frac = 0;   move16 (); 
+            }
+        }
+        else
+            /* bfi == 1 */
+        {
+            T0 = old_T0;        move16 (); 
+            *T0_frac = 0;       move16 (); 
+        }
+
+        /* find T0_min and T0_max for 2nd (or 4th) subframe */
+
+        T0_min = sub (T0, 5);
+        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);
+        }
+    }
+    else
+        /* second or fourth subframe */
+    {
+        test (); test (); 
+        /* if bfi == 0 decode pitch */
+        if ((bfi == 0) && (sub (index, 61) < 0))
+        {
+            /* i = (index+5)/6 - 1 */
+            i = sub (mult (add (index, 5), 5462), 1);
+            T0 = add (i, T0_min);
+            i = add (add (i, i), i);
+            *T0_frac = sub (sub (index, 3), add (i, i));
+                                move16 (); 
+        }
+        else
+            /* bfi == 1  OR index >= 61 */
+        {
+            T0 = old_T0;        move16 (); 
+            *T0_frac = 0;       move16 (); 
+        }
+    }
+
+    old_T0 = T0;                move16 (); 
+
+    return T0;
+}