--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/g_code.c	Wed Apr 03 05:31:37 2024 +0000
@@ -0,0 +1,77 @@
+/*************************************************************************
+ *
+ *  FUNCTION:   G_code
+ *
+ *  PURPOSE:  Compute the innovative codebook gain.
+ *
+ *  DESCRIPTION:
+ *      The innovative codebook gain is given by
+ *
+ *              g = <x[], y[]> / <y[], y[]>
+ *
+ *      where x[] is the target vector, y[] is the filtered innovative
+ *      codevector, and <> denotes dot product.
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+#include "cnst.h"
+
+Word16 G_code (         /* out   : Gain of innovation code         */
+    Word16 xn2[],       /* in    : target vector                   */
+    Word16 y2[]         /* in    : filtered innovation vector      */
+)
+{
+    Word16 i;
+    Word16 xy, yy, exp_xy, exp_yy, gain;
+    Word16 scal_y2[L_SUBFR];
+    Word32 s;
+
+    /* Scale down Y[] by 2 to avoid overflow */
+
+    for (i = 0; i < L_SUBFR; i++)
+    {
+        scal_y2[i] = shr (y2[i], 1);  move16 (); 
+    }
+
+    /* Compute scalar product <X[],Y[]> */
+
+    s = 1L;                           move32 (); /* Avoid case of all zeros */
+    for (i = 0; i < L_SUBFR; i++)
+    {
+        s = L_mac (s, xn2[i], scal_y2[i]);
+    }
+    exp_xy = norm_l (s);
+    xy = extract_h (L_shl (s, exp_xy));
+
+    /* If (xy < 0) gain = 0  */
+
+    test (); 
+    if (xy <= 0)
+        return ((Word16) 0);
+
+    /* Compute scalar product <Y[],Y[]> */
+
+    s = 0L;                           move32 (); 
+    for (i = 0; i < L_SUBFR; i++)
+    {
+        s = L_mac (s, scal_y2[i], scal_y2[i]);
+    }
+    exp_yy = norm_l (s);
+    yy = extract_h (L_shl (s, exp_yy));
+
+    /* compute gain = xy/yy */
+
+    xy = shr (xy, 1);                 /* Be sure xy < yy */
+    gain = div_s (xy, yy);
+
+    /* Denormalization of division */
+    i = add (exp_xy, 5);              /* 15-1+9-18 = 5 */
+    i = sub (i, exp_yy);
+
+    gain = shr (gain, i);
+
+    return (gain);
+}