--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/int_lsf.c	Mon May 06 05:45:31 2024 +0000
@@ -0,0 +1,112 @@
+/*
+********************************************************************************
+*
+*      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             : int_lsf.c
+*
+********************************************************************************
+*/
+/*
+********************************************************************************
+*                         MODULE INCLUDE FILE AND VERSION ID
+********************************************************************************
+*/
+#include "namespace.h"
+#include "int_lsf.h"
+ 
+/*
+********************************************************************************
+*                         INCLUDE FILES
+********************************************************************************
+*/
+#include "typedef.h"
+#include "basic_op.h"
+#include "no_count.h"
+#include "cnst.h"
+
+/*
+********************************************************************************
+*                         LOCAL VARIABLES AND TABLES
+********************************************************************************
+*/
+/*
+*--------------------------------------*
+* Constants (defined in cnst.h)        *
+*--------------------------------------*
+*  M         : LSF order               *
+*--------------------------------------*
+*/
+ 
+/*
+********************************************************************************
+*                         PUBLIC PROGRAM CODE
+********************************************************************************
+*/
+
+/*
+**************************************************************************
+*
+*  Function    : Int_lsf
+*  Purpose     : Interpolates the LSFs for selected subframe
+*  Description : The 20 ms speech frame is divided into 4 subframes.
+*                The LSFs are interpolated at the 1st, 2nd and 3rd
+*                subframe and only forwarded at the 4th subframe.
+*
+*                      |------|------|------|------|
+*                         sf1    sf2    sf3    sf4
+*                   F0                          F1
+*      
+*                 sf1:   3/4 F0 + 1/4 F1         sf3:   1/4 F0 + 3/4 F1
+*                 sf2:   1/2 F0 + 1/2 F1         sf4:       F1
+*  Returns     : void
+*
+**************************************************************************
+*/
+void Int_lsf(
+    Word16 lsf_old[], /* i : LSF vector at the 4th SF of past frame          */
+    Word16 lsf_new[], /* i : LSF vector at the 4th SF of present frame       */
+    Word16 i_subfr,   /* i : Pointer to current sf (equal to 0,40,80 or 120) */
+    Word16 lsf_out[]  /* o : interpolated LSF parameters for current sf      */
+)
+{
+    Word16 i;
+
+    if ( i_subfr == 0 )
+    {
+       test ();          
+       for (i = 0; i < M; i++) {
+          lsf_out[i] = add(sub(lsf_old[i], shr(lsf_old[i], 2)), shr(lsf_new[i], 2));
+          move16 ();
+       }
+    }
+    else if ( sub(i_subfr, 40) == 0 )
+    {
+       test (); test ();
+       for (i = 0; i < M; i++) {
+          lsf_out[i] = add(shr(lsf_old[i],1), shr(lsf_new[i], 1) );
+          move16 ();
+       }
+    }
+    else if ( sub(i_subfr, 80) == 0 )
+    {
+       test (); test (); test ();
+       for (i = 0; i < M; i++) {
+          lsf_out[i] = add(shr(lsf_old[i], 2), sub(lsf_new[i], shr(lsf_new[i], 2)));
+          move16 ();
+       }
+    }
+    else if ( sub(i_subfr, 120) == 0 )
+    {
+       test (); test (); test (); test ();                    
+       for (i = 0; i < M; i++) {
+          lsf_out[i] = lsf_new[i];                        move16 ();
+       }
+    }
+
+    return;
+}