gcc/ada/s-exnllf.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                       S Y S T E M . E X N _ L L F                        --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2005 Free Software Foundation, Inc.          --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 package body System.Exn_LLF is
  35
  36    -------------------------
  37    -- Exn_Long_Long_Float --
  38    -------------------------
  39
  40    function Exn_Long_Long_Float
  41      (Left  : Long_Long_Float;
  42       Right : Integer)
  43       return  Long_Long_Float
  44    is
  45       Result : Long_Long_Float := 1.0;
  46       Factor : Long_Long_Float := Left;
  47       Exp    : Integer := Right;
  48
  49    begin
  50       --  We use the standard logarithmic approach, Exp gets shifted right
  51       --  testing successive low order bits and Factor is the value of the
  52       --  base raised to the next power of 2. If the low order bit or Exp is
  53       --  set, multiply the result by this factor. For negative exponents,
  54       --  invert result upon return.
  55
  56       if Exp >= 0 then
  57          loop
  58             if Exp rem 2 /= 0 then
  59                Result := Result * Factor;
  60             end if;
  61
  62             Exp := Exp / 2;
  63             exit when Exp = 0;
  64             Factor := Factor * Factor;
  65          end loop;
  66
  67          return Result;
  68
  69       --  Here we have a negative exponent, and we compute the result as:
  70
  71       --     1.0 / (Left ** (-Right))
  72
  73       --  Note that the case of Left being zero is not special, it will
  74       --  simply result in a division by zero at the end, yielding a
  75       --  correctly signed infinity, or possibly generating an overflow.
  76
  77       --  Note on overflow: The coding of this routine assumes that the
  78       --  target generates infinities with standard IEEE semantics. If this
  79       --  is not the case, then the code below may raise Constraint_Error.
  80       --  This follows the implementation permission given in RM 4.5.6(12).
  81
  82       else
  83          begin
  84             loop
  85                if Exp rem 2 /= 0 then
  86                   Result := Result * Factor;
  87                end if;
  88
  89                Exp := Exp / 2;
  90                exit when Exp = 0;
  91                Factor := Factor * Factor;
  92             end loop;
  93
  94             return 1.0 / Result;
  95          end;
  96       end if;
  97    end Exn_Long_Long_Float;
  98
  99 end System.Exn_LLF;