1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUNTIME COMPONENTS                          --
4--                                                                          --
5--                        S Y S T E M . E X P L L I                         --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--          Copyright (C) 1992-2003 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
34package body System.Exp_LLI is
35
36   ---------------------------
37   -- Exp_Long_Long_Integer --
38   ---------------------------
39
40   --  Note that negative exponents get a constraint error because the
41   --  subtype of the Right argument (the exponent) is Natural.
42
43   function Exp_Long_Long_Integer
44     (Left  : Long_Long_Integer;
45      Right : Natural)
46      return  Long_Long_Integer
47   is
48      Result : Long_Long_Integer := 1;
49      Factor : Long_Long_Integer := Left;
50      Exp    : Natural := Right;
51
52   begin
53      --  We use the standard logarithmic approach, Exp gets shifted right
54      --  testing successive low order bits and Factor is the value of the
55      --  base raised to the next power of 2.
56
57      --  Note: it is not worth special casing base values -1, 0, +1 since
58      --  the expander does this when the base is a literal, and other cases
59      --  will be extremely rare.
60
61      if Exp /= 0 then
62         loop
63            if Exp rem 2 /= 0 then
64               declare
65                  pragma Unsuppress (All_Checks);
66               begin
67                  Result := Result * Factor;
68               end;
69            end if;
70
71            Exp := Exp / 2;
72            exit when Exp = 0;
73
74            declare
75               pragma Unsuppress (All_Checks);
76            begin
77               Factor := Factor * Factor;
78            end;
79         end loop;
80      end if;
81
82      return Result;
83   end Exp_Long_Long_Integer;
84
85end System.Exp_LLI;
86