1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                   G N A T . R A N D O M _ N U M B E R S                  --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 2007-2020, 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--  Extended pseudo-random number generation
33
34--  This package provides a type representing pseudo-random number generators,
35--  and subprograms to extract various distributions of numbers from them. It
36--  also provides types for representing initialization values and snapshots of
37--  internal generator state, which permit reproducible pseudo-random streams.
38
39--  The generator currently provided by this package has an extremely long
40--  period (at least 2**19937-1), and passes the Big Crush test suite, with the
41--  exception of the two linear complexity tests. Therefore, it is suitable for
42--  simulations, but should not be used as a cryptographic pseudo-random source
43--  without additional processing.
44
45--  The design of this package effects is simplified compared to the design
46--  of standard Ada.Numerics packages. There is no separate State type; the
47--  Generator type itself suffices for this purpose. The parameter modes on
48--  Reset procedures better reflect the effect of these routines.
49
50--  Note: this package is marked SPARK_Mode Off, because functions Random work
51--  by side-effect to change the value of the generator, hence they should not
52--  be called from SPARK code.
53
54with System.Random_Numbers;
55with Interfaces; use Interfaces;
56
57package GNAT.Random_Numbers with
58  SPARK_Mode => Off
59is
60   type Generator is limited private;
61   subtype Initialization_Vector is
62     System.Random_Numbers.Initialization_Vector;
63
64   function Random (Gen : Generator) return Float;
65   function Random (Gen : Generator) return Long_Float;
66   --  Return pseudo-random numbers uniformly distributed on [0 .. 1)
67
68   function Random (Gen : Generator) return Interfaces.Integer_32;
69   function Random (Gen : Generator) return Interfaces.Unsigned_32;
70   function Random (Gen : Generator) return Interfaces.Integer_64;
71   function Random (Gen : Generator) return Interfaces.Unsigned_64;
72   function Random (Gen : Generator) return Interfaces.Integer_128;
73   function Random (Gen : Generator) return Interfaces.Unsigned_128;
74   function Random (Gen : Generator) return Integer;
75   function Random (Gen : Generator) return Long_Integer;
76   --  Return pseudo-random numbers uniformly distributed on T'First .. T'Last
77   --  for various builtin integer types.
78
79   generic
80      type Result_Subtype is (<>);
81      Default_Min : Result_Subtype := Result_Subtype'Val (0);
82   function Random_Discrete
83     (Gen   : Generator;
84      Min   : Result_Subtype := Default_Min;
85      Max   : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
86   --  Returns pseudo-random numbers uniformly distributed on Min .. Max
87
88   generic
89      type Result_Subtype is delta <>;
90      Default_Min : Result_Subtype := 0.0;
91   function Random_Ordinary_Fixed
92     (Gen   : Generator;
93      Min   : Result_Subtype := Default_Min;
94      Max   : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
95   --  Returns pseudo-random numbers uniformly distributed on Min .. Max
96
97   generic
98      type Result_Subtype is delta <> digits <>;
99      Default_Min : Result_Subtype := 0.0;
100   function Random_Decimal_Fixed
101     (Gen   : Generator;
102      Min   : Result_Subtype := Default_Min;
103      Max   : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
104   --  Returns pseudo-random numbers uniformly distributed on Min .. Max
105
106   generic
107      type Result_Subtype is digits <>;
108   function Random_Float (Gen   : Generator) return Result_Subtype;
109   --  Returns pseudo-random numbers uniformly distributed on [0.0 .. 1.0)
110
111   function Random_Gaussian (Gen : Generator) return Long_Float;
112   function Random_Gaussian (Gen : Generator) return Float;
113   --  Returns pseudo-random numbers normally distributed value with mean 0
114   --  and standard deviation 1.0.
115
116   procedure Reset (Gen : out Generator);
117   --  Re-initialize the state of Gen from the time of day
118
119   procedure Reset
120     (Gen       : out Generator;
121      Initiator : Initialization_Vector);
122   procedure Reset
123     (Gen       : out Generator;
124      Initiator : Interfaces.Integer_32);
125   procedure Reset
126     (Gen       : out Generator;
127      Initiator : Interfaces.Unsigned_32);
128   procedure Reset
129     (Gen       : out Generator;
130      Initiator : Integer);
131   --  Re-initialize Gen based on the Initiator in various ways. Identical
132   --  values of Initiator cause identical sequences of values.
133
134   procedure Reset (Gen : out Generator; From_State : Generator);
135   --  Causes the state of Gen to be identical to that of From_State; Gen
136   --  and From_State will produce identical sequences of values subsequently.
137
138   procedure Reset (Gen : out Generator; From_Image : String);
139   function Image (Gen : Generator) return String;
140   --  The call
141   --     Reset (Gen2, Image (Gen1))
142   --  has the same effect as Reset (Gen2, Gen1);
143
144   Max_Image_Width : constant :=
145     System.Random_Numbers.Max_Image_Width + 2 + 20 + 5;
146   --  Maximum possible length of result of Image (...)
147
148private
149
150   type Generator is limited record
151      Rep : System.Random_Numbers.Generator;
152
153      Have_Gaussian : Boolean;
154      --  The algorithm used for Random_Gaussian produces deviates in
155      --  pairs. Have_Gaussian is true iff Random_Gaussian has returned one
156      --  member of the pair and Next_Gaussian contains the other.
157
158      Next_Gaussian : Long_Float;
159      --  Next random deviate to be produced by Random_Gaussian, if
160      --  Have_Gaussian.
161   end record;
162
163end GNAT.Random_Numbers;
164