--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/dec_lag6.c	Sun May 05 22:44:00 2024 +0000
@@ -0,0 +1,117 @@
+/*
+********************************************************************************
+*
+*      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             : dec_lag6.c
+*      Purpose          : Decoding of fractional pitch lag with 1/6 resolution.
+*
+********************************************************************************
+*/
+ 
+ 
+/*
+********************************************************************************
+*                         MODULE INCLUDE FILE AND VERSION ID
+********************************************************************************
+*/
+#include "namespace.h"
+#include "dec_lag6.h"
+ 
+/*
+********************************************************************************
+*                         INCLUDE FILES
+********************************************************************************
+*/
+#include "typedef.h"
+#include "basic_op.h"
+#include "no_count.h"
+ 
+/*
+********************************************************************************
+*                         PUBLIC PROGRAM CODE
+********************************************************************************
+*/
+/*
+************************************************************************
+*   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 (actually from previous frame) is used.
+*
+************************************************************************
+*/
+void Dec_lag6 (
+    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 *T0,        /* in/out: integer part of pitch lag      */
+    Word16 *T0_frac    /* output: fractional part of pitch lag   */
+)
+{
+    Word16 i;
+    Word16 T0_min, T0_max;
+
+    test ();
+    if (i_subfr == 0)          /* if 1st or 3rd subframe */
+    {
+       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
+       /* second or fourth subframe */
+    {
+       /* 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);
+       }
+       
+       /* 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 (); 
+    }
+}