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) 1992-2012, 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 3,  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.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 package body System.Exn_LLF is
  33
  34    -------------------------
  35    -- Exn_Long_Long_Float --
  36    -------------------------
  37
  38    function Exn_Long_Long_Float
  39      (Left  : Long_Long_Float;
  40       Right : Integer) return Long_Long_Float
  41    is
  42       Result : Long_Long_Float := 1.0;
  43       Factor : Long_Long_Float := Left;
  44       Exp    : Integer := Right;
  45
  46    begin
  47       --  We use the standard logarithmic approach, Exp gets shifted right
  48       --  testing successive low order bits and Factor is the value of the
  49       --  base raised to the next power of 2. If the low order bit or Exp is
  50       --  set, multiply the result by this factor. For negative exponents,
  51       --  invert result upon return.
  52
  53       if Exp >= 0 then
  54          loop
  55             if Exp rem 2 /= 0 then
  56                Result := Result * Factor;
  57             end if;
  58
  59             Exp := Exp / 2;
  60             exit when Exp = 0;
  61             Factor := Factor * Factor;
  62          end loop;
  63
  64          return Result;
  65
  66       --  Here we have a negative exponent, and we compute the result as:
  67
  68       --     1.0 / (Left ** (-Right))
  69
  70       --  Note that the case of Left being zero is not special, it will
  71       --  simply result in a division by zero at the end, yielding a
  72       --  correctly signed infinity, or possibly generating an overflow.
  73
  74       --  Note on overflow: The coding of this routine assumes that the
  75       --  target generates infinities with standard IEEE semantics. If this
  76       --  is not the case, then the code below may raise Constraint_Error.
  77       --  This follows the implementation permission given in RM 4.5.6(12).
  78
  79       else
  80          begin
  81             loop
  82                if Exp rem 2 /= 0 then
  83                   Result := Result * Factor;
  84                end if;
  85
  86                Exp := Exp / 2;
  87                exit when Exp = 0;
  88                Factor := Factor * Factor;
  89             end loop;
  90
  91             return 1.0 / Result;
  92          end;
  93       end if;
  94    end Exn_Long_Long_Float;
  95
  96 end System.Exn_LLF;