--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmefr/pred_lt6.c	Fri Nov 25 16:18:21 2022 +0000
@@ -0,0 +1,80 @@
+/*************************************************************************
+ *
+ *  FUNCTION:   Pred_lt_6()
+ *
+ *  PURPOSE:  Compute the result of long term prediction with fractional
+ *            interpolation of resolution 1/6. (Interpolated past excitation).
+ *
+ *  DESCRIPTION:
+ *       The past excitation signal at the given delay is interpolated at
+ *       the given fraction to build the adaptive codebook excitation.
+ *       On return exc[0..L_subfr-1] contains the interpolated signal
+ *       (adaptive codebook excitation).
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+#define UP_SAMP      6
+#define L_INTERPOL   10
+#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] =
+{
+    29443,
+    28346, 25207, 20449, 14701, 8693, 3143,
+    -1352, -4402, -5865, -5850, -4673, -2783,
+    -672, 1211, 2536, 3130, 2991, 2259,
+    1170, 0, -1001, -1652, -1868, -1666,
+    -1147, -464, 218, 756, 1060, 1099,
+    904, 550, 135, -245, -514, -634,
+    -602, -451, -231, 0, 191, 308,
+    340, 296, 198, 78, -36, -120,
+    -163, -165, -132, -79, -19, 34,
+    73, 91, 89, 70, 38, 0
+};
+
+void Pred_lt_6 (
+    Word16 exc[],     /* in/out: excitation buffer */
+    Word16 T0,        /* input : integer pitch lag */
+    Word16 frac,      /* input : fraction of lag   */
+    Word16 L_subfr    /* input : subframe size     */
+)
+{
+    Word16 i, j, k;
+    Word16 *x0, *x1, *x2;
+    const Word16 *c1, *c2;
+    Word32 s;
+
+    x0 = &exc[-T0];             move16 (); 
+
+    frac = negate (frac);
+    test (); 
+    if (frac < 0)
+    {
+        frac = add (frac, UP_SAMP);
+        x0--;
+    }
+    for (j = 0; j < L_subfr; j++)
+    {
+        x1 = x0++;              move16 (); 
+        x2 = x0;                move16 (); 
+        c1 = &inter_6[frac];
+        c2 = &inter_6[sub (UP_SAMP, frac)];
+
+        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]);
+        }
+
+        exc[j] = round (s);     move16 (); 
+    }
+
+    return;
+}