--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmefr/convolve.c	Fri Nov 25 16:18:21 2022 +0000
@@ -0,0 +1,43 @@
+/*************************************************************************
+ *
+ *  FUNCTION:   Convolve
+ *
+ *  PURPOSE:
+ *     Perform the convolution between two vectors x[] and h[] and
+ *     write the result in the vector y[]. All vectors are of length L
+ *     and only the first L samples of the convolution are computed.
+ *
+ *  DESCRIPTION:
+ *     The convolution is given by
+ *
+ *          y[n] = sum_{i=0}^{n} x[i] h[n-i],        n=0,...,L-1
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+void Convolve (
+    Word16 x[],        /* (i)     : input vector                           */
+    Word16 h[],        /* (i)     : impulse response                       */
+    Word16 y[],        /* (o)     : output vector                          */
+    Word16 L           /* (i)     : vector size                            */
+)
+{
+    Word16 i, n;
+    Word32 s;
+
+    for (n = 0; n < L; n++)
+    {
+        s = 0;                  move32 (); 
+        for (i = 0; i <= n; i++)
+        {
+            s = L_mac (s, x[i], h[n - i]);
+        }
+        s = L_shl (s, 3);
+        y[n] = extract_h (s);   move16 (); 
+    }
+
+    return;
+}