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File : s-expuns.adb


------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUNTIME COMPONENTS                          --
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------------------------------------------------------------------------------

with System.Unsigned_Types; use System.Unsigned_Types;

package body System.Exp_Uns is

   ------------------
   -- Exp_Unsigned --
   ------------------

   function Exp_Unsigned
     (Left  : Unsigned;
      Right : Natural)
      return  Unsigned
   is
      Result  : Unsigned := 1;
      Factor  : Unsigned := Left;
      Exp     : Natural := Right;

   begin
      --  We use the standard logarithmic approach, Exp gets shifted right
      --  testing successive low order bits and Factor is the value of the
      --  base raised to the next power of 2.

      --  Note: it is not worth special casing the cases of base values -1,0,+1
      --  since the expander does this when the base is a literal, and other
      --  cases will be extremely rare.

      if Exp /= 0 then
         loop
            if Exp rem 2 /= 0 then
               Result := Result * Factor;
            end if;

            Exp := Exp / 2;
            exit when Exp = 0;
            Factor := Factor * Factor;
         end loop;
      end if;

      return Result;
   end Exp_Unsigned;

end System.Exp_Uns;