--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmefr/pow2.c	Fri Nov 25 16:18:21 2022 +0000
@@ -0,0 +1,45 @@
+/*************************************************************************
+ *
+ *   FUNCTION:  Pow2()
+ *
+ *   PURPOSE: computes  L_x = pow(2.0, exponent.fraction)
+ *
+ *   DESCRIPTION:
+ *       The function Pow2(L_x) is approximated by a table and linear
+ *       interpolation.
+ *          1- i = bit10-b15 of fraction,   0 <= i <= 31
+ *          2- a = bit0-b9   of fraction   
+ *          3- L_x = table[i]<<16 - (table[i] - table[i+1]) * a * 2
+ *          4- L_x = L_x >> (30-exponent)     (with rounding)
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+
+#include "pow2.tab"     /* Table for Pow2() */
+
+Word32 Pow2 (           /* (o)  : result       (range: 0<=val<=0x7fffffff) */
+    Word16 exponent,    /* (i)  : Integer part.      (range: 0<=val<=30)   */
+    Word16 fraction     /* (i)  : Fractional part.  (range: 0.0<=val<1.0) */
+)
+{
+    Word16 exp, i, a, tmp;
+    Word32 L_x;
+
+    L_x = L_mult (fraction, 32);/* L_x = fraction<<6           */
+    i = extract_h (L_x);        /* Extract b10-b16 of fraction */
+    L_x = L_shr (L_x, 1);
+    a = extract_l (L_x);        /* Extract b0-b9   of fraction */
+    a = a & (Word16) 0x7fff;    logic16 (); 
+
+    L_x = L_deposit_h (table[i]);       /* table[i] << 16        */
+    tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */
+    L_x = L_msu (L_x, tmp, a);  /* L_x -= tmp*a*2        */
+
+    exp = sub (30, exponent);
+    L_x = L_shr_r (L_x, exp);
+
+    return (L_x);
+}