1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME COMPONENTS --
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 --
9 -- Copyright (C) 1992-2003 Free Software Foundation, Inc. --
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. --
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, 59 Temple Place - Suite 330, Boston, --
24 -- MA 02111-1307, USA. --
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. --
33 -- GNAT was originally developed by the GNAT team at New York University. --
34 -- Extensive contributions were provided by Ada Core Technologies Inc. --
36 ------------------------------------------------------------------------------
38 -- Note: the implementation used in this package was contributed by
39 -- Robert Eachus. It is based on the work of L. Blum, M. Blum, and
40 -- M. Shub, SIAM Journal of Computing, Vol 15. No 2, May 1986. The
41 -- particular choices for P and Q chosen here guarantee a period of
42 -- 562,085,314,430,582 (about 2**49), and the generated sequence has
43 -- excellent randomness properties. For further details, see the
44 -- paper "Fast Generation of Trustworthy Random Numbers", by Robert
45 -- Eachus, which describes both the algorithm and the efficient
46 -- implementation approach used here.
51 type Result_Subtype
is (<>);
53 package Ada
.Numerics
.Discrete_Random
is
55 -- The algorithm used here is reliable from a required statistical point
56 -- of view only up to 48 bits. We try to behave reasonably in the case
57 -- of larger types, but we can't guarantee the required properties.
58 -- So generate a warning for these (slightly) dubious cases.
60 pragma Compile_Time_Warning
61 (Result_Subtype
'Size > 48,
62 "statistical properties not guaranteed for size '> 48");
66 type Generator
is limited private;
68 function Random
(Gen
: Generator
) return Result_Subtype
;
70 procedure Reset
(Gen
: Generator
);
71 procedure Reset
(Gen
: Generator
; Initiator
: Integer);
73 -- Advanced facilities.
75 type State
is private;
77 procedure Save
(Gen
: Generator
; To_State
: out State
);
78 procedure Reset
(Gen
: Generator
; From_State
: State
);
80 Max_Image_Width
: constant := 80;
82 function Image
(Of_State
: State
) return String;
83 function Value
(Coded_State
: String) return State
;
86 subtype Int
is Interfaces
.Integer_32
;
87 subtype Rst
is Result_Subtype
;
89 -- We prefer to use 14 digits for Flt, but some targets are more limited
91 type Flt
is digits Positive'Min (14, Long_Long_Float'Digits);
93 RstF
: constant Flt
:= Flt
(Rst
'Pos (Rst
'First));
94 RstL
: constant Flt
:= Flt
(Rst
'Pos (Rst
'Last));
96 Offs
: constant Flt
:= RstF
- 0.5;
98 K1
: constant := 94_833_359
;
99 K1F
: constant := 94_833_359
.0
;
100 K2
: constant := 47_416_679
;
101 K2F
: constant := 47_416_679
.0
;
102 Scal
: constant Flt
:= (RstL
- RstF
+ 1.0) / (K1F
* K2F
);
105 X1
: Int
:= Int
(2999 ** 2);
106 X2
: Int
:= Int
(1439 ** 2);
113 type Generator
is limited record
117 end Ada
.Numerics
.Discrete_Random
;