--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/autocorr.c	Fri Apr 05 06:08:15 2024 +0000
@@ -0,0 +1,130 @@
+/*
+********************************************************************************
+*
+*      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             : autocorr.c
+*
+********************************************************************************
+*/
+/*
+********************************************************************************
+*                         MODULE INCLUDE FILE AND VERSION ID
+********************************************************************************
+*/
+#include "namespace.h"
+#include "autocorr.h"
+const char autocorr_id[] = "@(#)$Id $" autocorr_h;
+ 
+/*
+********************************************************************************
+*                         INCLUDE FILES
+********************************************************************************
+*/
+#include "typedef.h"
+#include "basic_op.h"
+#include "oper_32b.h"
+#include "no_count.h"
+#include "cnst.h"
+
+/*
+********************************************************************************
+*                         LOCAL VARIABLES AND TABLES
+********************************************************************************
+*/
+ 
+/*
+********************************************************************************
+*                         PUBLIC PROGRAM CODE
+********************************************************************************
+*/
+/*
+**************************************************************************
+*
+*  Function    : autocorr
+*  Purpose     : Compute autocorrelations of signal with windowing
+*
+**************************************************************************
+*/
+Word16 Autocorr (
+    Word16 x[],            /* (i)    : Input signal (L_WINDOW)            */
+    Word16 m,              /* (i)    : LPC order                          */
+    Word16 r_h[],          /* (o)    : Autocorrelations  (msb)            */
+    Word16 r_l[],          /* (o)    : Autocorrelations  (lsb)            */
+    const Word16 wind[]    /* (i)    : window for LPC analysis (L_WINDOW) */
+)
+{
+    Word16 i, j, norm;
+    Word16 y[L_WINDOW];
+    Word32 sum;
+    Word16 overfl, overfl_shft;
+
+    /* Windowing of signal */
+
+    for (i = 0; i < L_WINDOW; i++)
+    {
+        y[i] = mult_r (x[i], wind[i]); move16 (); 
+    }
+
+    /* Compute r[0] and test for overflow */
+
+    overfl_shft = 0;                   move16 (); 
+
+    do
+    {
+        overfl = 0;                    move16 (); 
+        sum = 0L;                      move32 ();
+
+        for (i = 0; i < L_WINDOW; i++)
+        {
+            sum = L_mac (sum, y[i], y[i]);
+        }
+
+        /* If overflow divide y[] by 4 */
+
+        test (); 
+        if (L_sub (sum, MAX_32) == 0L)
+        {
+            overfl_shft = add (overfl_shft, 4);
+            overfl = 1;                move16 (); /* Set the overflow flag */
+
+            for (i = 0; i < L_WINDOW; i++)
+            {
+                y[i] = shr (y[i], 2);  move16 (); 
+            }
+        }
+        test (); 
+    }
+    while (overfl != 0);
+
+    sum = L_add (sum, 1L);             /* Avoid the case of all zeros */
+
+    /* Normalization of r[0] */
+
+    norm = norm_l (sum);
+    sum = L_shl (sum, norm);
+    L_Extract (sum, &r_h[0], &r_l[0]); /* Put in DPF format (see oper_32b) */
+
+    /* r[1] to r[m] */
+
+    for (i = 1; i <= m; i++)
+    {
+        sum = 0;                       move32 (); 
+
+        for (j = 0; j < L_WINDOW - i; j++)
+        {
+            sum = L_mac (sum, y[j], y[j + i]);
+        }
+
+        sum = L_shl (sum, norm);
+        L_Extract (sum, &r_h[i], &r_l[i]);
+    }
+
+    norm = sub (norm, overfl_shft);
+
+    return norm;
+}