File : s-exnllf.adb
------------------------------------------------------------------------------
-- --
-- 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. --
-- --
-- --
-- --
-- --
-- --
-- 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;