gcc/ada/s-expint.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                        S Y S T E M . E X P I N T                         --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2009 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.Exp_Int is
  33
  34    -----------------
  35    -- Exp_Integer --
  36    -----------------
  37
  38    --  Note that negative exponents get a constraint error because the
  39    --  subtype of the Right argument (the exponent) is Natural.
  40
  41    function Exp_Integer
  42      (Left  : Integer;
  43       Right : Natural)
  44       return  Integer
  45    is
  46       Result : Integer := 1;
  47       Factor : Integer := Left;
  48       Exp    : Natural := Right;
  49
  50    begin
  51       --  We use the standard logarithmic approach, Exp gets shifted right
  52       --  testing successive low order bits and Factor is the value of the
  53       --  base raised to the next power of 2.
  54
  55       --  Note: it is not worth special casing base values -1, 0, +1 since
  56       --  the expander does this when the base is a literal, and other cases
  57       --  will be extremely rare.
  58
  59       if Exp /= 0 then
  60          loop
  61             if Exp rem 2 /= 0 then
  62                declare
  63                   pragma Unsuppress (All_Checks);
  64                begin
  65                   Result := Result * Factor;
  66                end;
  67             end if;
  68
  69             Exp := Exp / 2;
  70             exit when Exp = 0;
  71
  72             declare
  73                pragma Unsuppress (All_Checks);
  74             begin
  75                Factor := Factor * Factor;
  76             end;
  77          end loop;
  78       end if;
  79
  80       return Result;
  81    end Exp_Integer;
  82
  83 end System.Exp_Int;