File : g-mbdira.ads
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 -- --
23 -- --
24 -- --
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
49 with Interfaces;
50
51 generic
52 type Result_Subtype is (<>);
53
54 package 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
86 private
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
123 end GNAT.MBBS_Discrete_Random;