1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--            G N A T . M B B S _ D I S C R E T E _ R A N D O M             --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2010, Free Software Foundation, Inc.         --
10--                                                                          --
11-- This specification is derived from the Ada Reference Manual for use with --
12-- GNAT. The copyright notice above, and the license provisions that follow --
13-- apply solely to the  contents of the part following the private keyword. --
14--                                                                          --
15-- GNAT is free software;  you can  redistribute it  and/or modify it under --
16-- terms of the  GNU General Public License as published  by the Free Soft- --
17-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
18-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
19-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
20-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
21--                                                                          --
22-- As a special exception under Section 7 of GPL version 3, you are granted --
23-- additional permissions described in the GCC Runtime Library Exception,   --
24-- version 3.1, as published by the Free Software Foundation.               --
25--                                                                          --
26-- You should have received a copy of the GNU General Public License and    --
27-- a copy of the GCC Runtime Library Exception along with this program;     --
28-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
29-- <http://www.gnu.org/licenses/>.                                          --
30--                                                                          --
31-- GNAT was originally developed  by the GNAT team at  New York University. --
32-- Extensive contributions were provided by Ada Core Technologies Inc.      --
33--                                                                          --
34------------------------------------------------------------------------------
35
36--  The implementation used in this package was contributed by Robert
37--  Eachus. It is based on the work of L. Blum, M. Blum, and M. Shub, SIAM
38--  Journal of Computing, Vol 15. No 2, May 1986. The particular choices for P
39--  and Q chosen here guarantee a period of 562,085,314,430,582 (about 2**49),
40--  and the generated sequence has excellent randomness properties. For further
41--  details, see the paper "Fast Generation of Trustworthy Random Numbers", by
42--  Robert Eachus, which describes both the algorithm and the efficient
43--  implementation approach used here.
44
45--  Formerly, this package was Ada.Numerics.Discrete_Random. It is retained
46--  here in part to allow users to reconstruct number sequences generated
47--  by previous versions.
48
49with Interfaces;
50
51generic
52   type Result_Subtype is (<>);
53
54package GNAT.MBBS_Discrete_Random is
55
56   --  The algorithm used here is reliable from a required statistical point of
57   --  view only up to 48 bits. We try to behave reasonably in the case of
58   --  larger types, but we can't guarantee the required properties. So
59   --  generate a warning for these (slightly) dubious cases.
60
61   pragma Compile_Time_Warning
62     (Result_Subtype'Size > 48,
63      "statistical properties not guaranteed for size > 48");
64
65   --  Basic facilities
66
67   type Generator is limited private;
68
69   function Random (Gen : Generator) return Result_Subtype;
70
71   procedure Reset (Gen : Generator);
72   procedure Reset (Gen : Generator; Initiator : Integer);
73
74   --  Advanced facilities
75
76   type State is private;
77
78   procedure Save  (Gen : Generator; To_State   : out State);
79   procedure Reset (Gen : Generator; From_State : State);
80
81   Max_Image_Width : constant := 80;
82
83   function Image (Of_State    : State)  return String;
84   function Value (Coded_State : String) return State;
85
86private
87   subtype Int is Interfaces.Integer_32;
88   subtype Rst is Result_Subtype;
89
90   --  We prefer to use 14 digits for Flt, but some targets are more limited
91
92   type Flt is digits Positive'Min (14, Long_Long_Float'Digits);
93
94   RstF : constant Flt := Flt (Rst'Pos (Rst'First));
95   RstL : constant Flt := Flt (Rst'Pos (Rst'Last));
96
97   Offs : constant Flt := RstF - 0.5;
98
99   K1   : constant := 94_833_359;
100   K1F  : constant := 94_833_359.0;
101   K2   : constant := 47_416_679;
102   K2F  : constant := 47_416_679.0;
103   Scal : constant Flt := (RstL - RstF + 1.0) / (K1F * K2F);
104
105   type State is record
106      X1  : Int := Int (2999 ** 2);
107      X2  : Int := Int (1439 ** 2);
108      P   : Int := K1;
109      Q   : Int := K2;
110      FP  : Flt := K1F;
111      Scl : Flt := Scal;
112   end record;
113
114   type Writable_Access (Self : access Generator) is limited null record;
115   --  Auxiliary type to make Generator a self-referential type
116
117   type Generator is limited record
118      Writable  : Writable_Access (Generator'Access);
119      --  This self reference allows functions to modify Generator arguments
120      Gen_State : State;
121   end record;
122
123end GNAT.MBBS_Discrete_Random;
124