1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME 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) 1992-2018, 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
32package body System.Exp_LLI is
33
34   ---------------------------
35   -- Exp_Long_Long_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_Long_Long_Integer
42     (Left  : Long_Long_Integer;
43      Right : Natural)
44      return  Long_Long_Integer
45   is
46      Result : Long_Long_Integer := 1;
47      Factor : Long_Long_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_Long_Long_Integer;
82
83end System.Exp_LLI;
84