--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmefr/inter_6.c	Fri Nov 25 16:18:21 2022 +0000
@@ -0,0 +1,57 @@
+/*************************************************************************
+ *
+ *  FUNCTION:  Interpol_6()
+ *
+ *  PURPOSE:  Interpolating the normalized correlation with 1/6 resolution.
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+#define UP_SAMP      6
+#define L_INTERPOL   4
+#define FIR_SIZE     (UP_SAMP*L_INTERPOL+1)
+
+/* 1/6 resolution interpolation filter  (-3 dB at 3600 Hz) */
+
+static const Word16 inter_6[FIR_SIZE] =
+{
+    29519,
+    28316, 24906, 19838, 13896, 7945, 2755,
+    -1127, -3459, -4304, -3969, -2899, -1561,
+    -336, 534, 970, 1023, 823, 516,
+    220, 0, -131, -194, -215, 0
+};
+
+Word16 Interpol_6 (  /* (o)  : interpolated value  */
+    Word16 *x,       /* (i)  : input vector        */
+    Word16 frac      /* (i)  : fraction            */
+)
+{
+    Word16 i, k;
+    Word16 *x1, *x2;
+    const Word16 *c1, *c2;
+    Word32 s;
+
+    test (); 
+    if (frac < 0)
+    {
+        frac = add (frac, UP_SAMP);
+        x--;
+    }
+    x1 = &x[0];                         move16 (); 
+    x2 = &x[1];                         move16 (); 
+    c1 = &inter_6[frac];                move16 (); 
+    c2 = &inter_6[sub (UP_SAMP, frac)]; move16 (); 
+
+    s = 0;                              move32 (); 
+    for (i = 0, k = 0; i < L_INTERPOL; i++, k += UP_SAMP)
+    {
+        s = L_mac (s, x1[-i], c1[k]);
+        s = L_mac (s, x2[i], c2[k]);
+    }
+
+    return round (s);
+}