--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/pre_proc.c	Mon May 06 19:02:44 2024 +0000
@@ -0,0 +1,116 @@
+/*
+********************************************************************************
+*
+*      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             : pre_proc.c
+*      Purpose          : Preprocessing of input speech.
+*
+********************************************************************************
+*/
+
+/*
+********************************************************************************
+*                         MODULE INCLUDE FILE AND VERSION ID
+********************************************************************************
+*/
+#include "namespace.h"
+#include "pre_proc.h"
+
+/*
+********************************************************************************
+*                         INCLUDE FILES
+********************************************************************************
+*/
+#include "typedef.h"
+#include "basic_op.h"
+#include "oper_32b.h"
+#include "no_count.h"
+
+/*
+********************************************************************************
+*                         LOCAL VARIABLES AND TABLES
+********************************************************************************
+*/
+/* filter coefficients (fc = 80 Hz, coeff. b[] is divided by 2) */
+static const Word16 b[3] = {1899, -3798, 1899};
+static const Word16 a[3] = {4096, 7807, -3733};
+
+/*
+********************************************************************************
+*                         PUBLIC PROGRAM CODE
+********************************************************************************
+*/
+ 
+/*************************************************************************
+*
+*  Function:   Pre_Process_reset
+*  Purpose:    Initializes state memory to zero
+*
+**************************************************************************
+*/
+void Pre_Process_reset (Pre_ProcessState *state)
+{
+  state->y2_hi = 0;
+  state->y2_lo = 0;
+  state->y1_hi = 0;
+  state->y1_lo = 0;
+  state->x0 = 0;
+  state->x1 = 0;
+}
+ 
+/*************************************************************************
+ *
+ *  FUNCTION:  Pre_Process()
+ *
+ *  PURPOSE: Preprocessing of input speech.
+ *
+ *  DESCRIPTION:
+ *     - 2nd order high pass filtering with cut off frequency at 80 Hz.
+ *     - Divide input by two.
+ *
+ *                                                                        
+ * Algorithm:                                                             
+ *                                                                        
+ *  y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b[2]*x[i-2]/2                    
+ *                     + a[1]*y[i-1]   + a[2]*y[i-2];                     
+ *                                                                        
+ *                                                                        
+ *  Input is divided by two in the filtering process.
+ *
+ *************************************************************************/
+int Pre_Process (
+    Pre_ProcessState *st,
+    Word16 signal[], /* input/output signal */
+    Word16 lg)       /* lenght of signal    */
+{
+    Word16 i, x2;
+    Word32 L_tmp;
+
+    for (i = 0; i < lg; i++)
+    {
+        x2 = st->x1;                   move16 (); 
+        st->x1 = st->x0;               move16 (); 
+        st->x0 = signal[i];            move16 (); 
+
+        /*  y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b140[2]*x[i-2]/2  */
+        /*                     + a[1]*y[i-1] + a[2] * y[i-2];      */
+
+        L_tmp = Mpy_32_16 (st->y1_hi, st->y1_lo, a[1]);
+        L_tmp = L_add (L_tmp, Mpy_32_16 (st->y2_hi, st->y2_lo, a[2]));
+        L_tmp = L_mac (L_tmp, st->x0, b[0]);
+        L_tmp = L_mac (L_tmp, st->x1, b[1]);
+        L_tmp = L_mac (L_tmp, x2, b[2]);
+        L_tmp = L_shl (L_tmp, 3);
+        signal[i] = round (L_tmp); move16 (); 
+
+        st->y2_hi = st->y1_hi;             move16 (); 
+        st->y2_lo = st->y1_lo;             move16 (); 
+        L_Extract (L_tmp, &st->y1_hi, &st->y1_lo);
+    }
+    return 0;
+}