Use exponentiation by squaring instead of n-times multiplications in power() (#385)

amxmodx/power.cpp

@@ -19,10 +19,19 @@ static cell power(AMX *amx, cell *params)
   /* power(value, exponent);
    *   params[1] = value
    *   params[2] = exponent
+   * Exponentiation by squaring
    */
   cell result = 1;
-  while (params[2]-- > 0)
-    result *= params[1];
+  cell value = params[1];
+  cell exp = params[2];
+  while (exp > 0) {
+    if (exp & 1) {
+      result *= value;
+    } /* if */
+    value *= value;
+    exp >>= 1;
+  } /* while */
+
   return result;
 }