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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                       S Y S T E M . E X N _ L L F                        --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--          Copyright (C) 1992-2009 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 3,  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.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

package body System.Exn_LLF is

   -------------------------

   -- Exn_Long_Long_Float --

   -------------------------

   function Exn_Long_Long_Float

     (Left  : Long_Long_Float;

      Right : Integer)

      return  Long_Long_Float

   is

      Result : Long_Long_Float := 1.0;

      Factor : Long_Long_Float := Left;

      Exp    : Integer := 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. If the low order bit or Exp is

      --  set, multiply the result by this factor. For negative exponents,

      --  invert result upon return.

      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;

         return Result;

      --  Here we have a negative exponent, and we compute the result as:

      --     1.0 / (Left ** (-Right))

      --  Note that the case of Left being zero is not special, it will

      --  simply result in a division by zero at the end, yielding a

      --  correctly signed infinity, or possibly generating an overflow.

      --  Note on overflow: The coding of this routine assumes that the

      --  target generates infinities with standard IEEE semantics. If this

      --  is not the case, then the code below may raise Constraint_Error.

      --  This follows the implementation permission given in RM 4.5.6(12).

      else

         begin

            loop

               if Exp rem 2 /= 0 then

                  Result := Result * Factor;

               end if;

               Exp := Exp / 2;

               exit when Exp = 0;

               Factor := Factor * Factor;

            end loop;

            return 1.0 / Result;

         end;

      end if;

   end Exn_Long_Long_Float;

end System.Exn_LLF;