------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUNTIME COMPONENTS                          --
--                                                                          --
--                        S Y S T E M . E X P I N T                         --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 1992-2003 Free Software Foundation, Inc.          --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
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-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
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-- MA 02111-1307, USA.                                                      --
--                                                                          --
-- As a special exception,  if other files  instantiate  generics from this --
-- unit, or you link  this unit with other files  to produce an executable, --
-- this  unit  does not  by itself cause  the resulting  executable  to  be --
-- covered  by the  GNU  General  Public  License.  This exception does not --
-- however invalidate  any other reasons why  the executable file  might be --
-- covered by the  GNU Public License.                                      --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

package body System.Exp_Int is

   -----------------
   -- Exp_Integer --
   -----------------

   --  Note that negative exponents get a constraint error because the
   --  subtype of the Right argument (the exponent) is Natural.

   function Exp_Integer
     (Left  : Integer;
      Right : Natural)
      return  Integer
   is
      Result : Integer := 1;
      Factor : Integer := 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 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
               declare
                  pragma Unsuppress (All_Checks);
               begin
                  Result := Result * Factor;
               end;
            end if;

            Exp := Exp / 2;
            exit when Exp = 0;

            declare
               pragma Unsuppress (All_Checks);
            begin
               Factor := Factor * Factor;
            end;
         end loop;
      end if;

      return Result;
   end Exp_Integer;

end System.Exp_Int;
