--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmefr/preemph.c	Fri Nov 25 16:18:21 2022 +0000
@@ -0,0 +1,36 @@
+/*---------------------------------------------------------------------*
+ * routine preemphasis()                                               *
+ * ~~~~~~~~~~~~~~~~~~~~~                                               *
+ * Preemphasis: filtering through 1 - g z^-1                           *
+ *---------------------------------------------------------------------*/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+Word16 mem_pre;
+
+void preemphasis (
+    Word16 *signal, /* (i/o)   : input signal overwritten by the output */
+    Word16 g,       /* (i)     : preemphasis coefficient                */
+    Word16 L        /* (i)     : size of filtering                      */
+)
+{
+    Word16 *p1, *p2, temp, i;
+
+    p1 = signal + L - 1;                    move16 (); 
+    p2 = p1 - 1;                            move16 (); 
+    temp = *p1;                             move16 (); 
+
+    for (i = 0; i <= L - 2; i++)
+    {
+        *p1 = sub (*p1, mult (g, *p2--));   move16 (); 
+        p1--;
+    }
+
+    *p1 = sub (*p1, mult (g, mem_pre));     move16 (); 
+
+    mem_pre = temp;                         move16 (); 
+
+    return;
+}