--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmefr/pre_proc.c	Fri Nov 25 16:18:21 2022 +0000
@@ -0,0 +1,80 @@
+/*************************************************************************
+ *
+ *  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.
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "oper_32b.h"
+#include "count.h"
+
+/*------------------------------------------------------------------------*
+ *                                                                        *
+ * 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.                     *
+ *------------------------------------------------------------------------*/
+
+/* 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};
+
+/* Static values to be preserved between calls */
+/* y[] values are kept in double precision     */
+
+static Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
+
+/* Initialization of static values */
+
+void Init_Pre_Process (void)
+{
+    y2_hi = 0;
+    y2_lo = 0;
+    y1_hi = 0;
+    y1_lo = 0;
+    x0 = 0;
+    x1 = 0;
+}
+
+void Pre_Process (
+    Word16 signal[], /* input/output signal */
+    Word16 lg)       /* lenght of signal    */
+{
+    Word16 i, x2;
+    Word32 L_tmp;
+
+    for (i = 0; i < lg; i++)
+    {
+        x2 = x1;                   move16 (); 
+        x1 = x0;                   move16 (); 
+        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 (y1_hi, y1_lo, a[1]);
+        L_tmp = L_add (L_tmp, Mpy_32_16 (y2_hi, y2_lo, a[2]));
+        L_tmp = L_mac (L_tmp, x0, b[0]);
+        L_tmp = L_mac (L_tmp, 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 (); 
+
+        y2_hi = y1_hi;             move16 (); 
+        y2_lo = y1_lo;             move16 (); 
+        L_Extract (L_tmp, &y1_hi, &y1_lo);
+    }
+    return;
+}