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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT RUN-TIME COMPONENTS --
4 -- --
5 -- A D A . N U M E R I C 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) 1992-2006, 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 2, 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. See the GNU General Public License --
21 -- for more details. You should have received a copy of the GNU General --
22 -- Public License distributed with GNAT; see file COPYING. If not, write --
23 -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
24 -- Boston, MA 02110-1301, USA. --
25 -- --
26 -- As a special exception, if other files instantiate generics from this --
27 -- unit, or you link this unit with other files to produce an executable, --
28 -- this unit does not by itself cause the resulting executable to be --
29 -- covered by the GNU General Public License. This exception does not --
30 -- however invalidate any other reasons why the executable file might be --
31 -- covered by the GNU Public License. --
32 -- --
33 -- GNAT was originally developed by the GNAT team at New York University. --
34 -- Extensive contributions were provided by Ada Core Technologies Inc. --
35 -- --
36 ------------------------------------------------------------------------------
38 -- Note: the implementation used in this package was contributed by Robert
39 -- Eachus. It is based on the work of L. Blum, M. Blum, and M. Shub, SIAM
40 -- Journal of Computing, Vol 15. No 2, May 1986. The particular choices for P
41 -- and Q chosen here guarantee a period of 562,085,314,430,582 (about 2**49),
42 -- and the generated sequence has excellent randomness properties. For further
43 -- details, see the paper "Fast Generation of Trustworthy Random Numbers", by
44 -- Robert Eachus, which describes both the algorithm and the efficient
45 -- implementation approach used here.
47 with Interfaces;
49 generic
50 type Result_Subtype is (<>);
52 package Ada.Numerics.Discrete_Random is
54 -- The algorithm used here is reliable from a required statistical point of
55 -- view only up to 48 bits. We try to behave reasonably in the case of
56 -- larger types, but we can't guarantee the required properties. So
57 -- generate a warning for these (slightly) dubious cases.
59 pragma Compile_Time_Warning
60 (Result_Subtype'Size > 48,
61 "statistical properties not guaranteed for size > 48");
63 -- Basic facilities
65 type Generator is limited private;
67 function Random (Gen : Generator) return Result_Subtype;
69 procedure Reset (Gen : Generator);
70 procedure Reset (Gen : Generator; Initiator : Integer);
72 -- Advanced facilities
74 type State is private;
76 procedure Save (Gen : Generator; To_State : out State);
77 procedure Reset (Gen : Generator; From_State : State);
79 Max_Image_Width : constant := 80;
81 function Image (Of_State : State) return String;
82 function Value (Coded_State : String) return State;
84 private
85 subtype Int is Interfaces.Integer_32;
86 subtype Rst is Result_Subtype;
88 -- We prefer to use 14 digits for Flt, but some targets are more limited
90 type Flt is digits Positive'Min (14, Long_Long_Float'Digits);
92 RstF : constant Flt := Flt (Rst'Pos (Rst'First));
93 RstL : constant Flt := Flt (Rst'Pos (Rst'Last));
95 Offs : constant Flt := RstF - 0.5;
97 K1 : constant := 94_833_359;
98 K1F : constant := 94_833_359.0;
99 K2 : constant := 47_416_679;
100 K2F : constant := 47_416_679.0;
101 Scal : constant Flt := (RstL - RstF + 1.0) / (K1F * K2F);
103 type State is record
104 X1 : Int := Int (2999 ** 2);
105 X2 : Int := Int (1439 ** 2);
106 P : Int := K1;
107 Q : Int := K2;
108 FP : Flt := K1F;
109 Scl : Flt := Scal;
110 end record;
112 type Generator is limited record
113 Gen_State : State;
114 end record;
116 end Ada.Numerics.Discrete_Random;