1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                S Y S T E M . S H A R E D _ B I G N U M S                 --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--            Copyright (C) 2012-2020, 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--  This package provides declarations shared across all instantiations of
33--  System.Generic_Bignums.
34
35with Ada.Unchecked_Conversion;
36with Interfaces;
37
38package System.Shared_Bignums is
39   pragma Preelaborate;
40
41   pragma Assert (Long_Long_Integer'Size = 64);
42   --  This package assumes that Long_Long_Integer size is 64 bit (i.e. that it
43   --  has a range of -2**63 to 2**63-1). The front end ensures that the mode
44   --  ELIMINATED is not allowed for overflow checking if this is not the case.
45
46   subtype Length is Natural range 0 .. 2 ** 23 - 1;
47   --  Represent number of words in Digit_Vector
48
49   Base : constant := 2 ** 32;
50   --  Digit vectors use this base
51
52   subtype SD is Interfaces.Unsigned_32;
53   --  Single length digit
54
55   type Digit_Vector is array (Length range <>) of SD;
56   --  Represent digits of a number (most significant digit first)
57
58   type Bignum_Data (Len : Length) is record
59      Neg : Boolean;
60      --  Set if value is negative, never set for zero
61
62      D : Digit_Vector (1 .. Len);
63      --  Digits of number, most significant first, represented in base
64      --  2**Base. No leading zeroes are stored, and the value of zero is
65      --  represented using an empty vector for D.
66   end record;
67
68   for Bignum_Data use record
69      Len at 0 range 0 .. 23;
70      Neg at 3 range 0 .. 7;
71   end record;
72
73   type Bignum is access all Bignum_Data;
74
75   function To_Bignum is new Ada.Unchecked_Conversion (System.Address, Bignum);
76
77   function To_Address is new
78     Ada.Unchecked_Conversion (Bignum, System.Address);
79
80end System.Shared_Bignums;
81