gcc/ada/s-expllu.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUNTIME COMPONENTS                          --
   4 --                                                                          --
   5 --                        S Y S T E M . X P _ B M L                         --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --        Copyright (C) 1992,1993,1994 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,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, 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 with System.Unsigned_Types; use System.Unsigned_Types;
  35
  36 package body System.Exp_LLU is
  37
  38    ----------------------------
  39    -- Exp_Long_Long_Unsigned --
  40    ----------------------------
  41
  42    function Exp_Long_Long_Unsigned
  43      (Left  : Long_Long_Unsigned;
  44       Right : Natural)
  45       return  Long_Long_Unsigned
  46    is
  47       Result : Long_Long_Unsigned := 1;
  48       Factor : Long_Long_Unsigned := Left;
  49       Exp    : Natural := Right;
  50
  51    begin
  52       --  We use the standard logarithmic approach, Exp gets shifted right
  53       --  testing successive low order bits and Factor is the value of the
  54       --  base raised to the next power of 2.
  55
  56       --  Note: it is not worth special casing the cases of base values -1,0,+1
  57       --  since the expander does this when the base is a literal, and other
  58       --  cases will be extremely rare.
  59
  60       if Exp /= 0 then
  61          loop
  62             if Exp rem 2 /= 0 then
  63                Result := Result * Factor;
  64             end if;
  65
  66             Exp := Exp / 2;
  67             exit when Exp = 0;
  68             Factor := Factor * Factor;
  69          end loop;
  70       end if;
  71
  72       return Result;
  73
  74    end Exp_Long_Long_Unsigned;
  75
  76 end System.Exp_LLU;