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) 1992-2010, Free Software Foundation, Inc. --
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. --
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. --
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/>. --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
30 ------------------------------------------------------------------------------
32 with System.Random_Numbers; use System.Random_Numbers;
34 package body Ada.Numerics.Discrete_Random is
36 -------------------------
37 -- Implementation Note --
38 -------------------------
40 -- The design of this spec is a bit awkward, as a result of Ada 95 not
41 -- permitting in-out parameters for function formals (most naturally
42 -- Generator values would be passed this way). In pure Ada 95, the only
43 -- solution would be to add a self-referential component to the generator
44 -- allowing access to the generator object from inside the function. This
45 -- would work because the generator is limited, which prevents any copy.
47 -- This is a bit heavy, so what we do is to use Unrestricted_Access to
48 -- get a pointer to the state in the passed Generator. This works because
49 -- Generator is a limited type and will thus always be passed by reference.
51 subtype Rep_Generator is System.Random_Numbers.Generator;
52 subtype Rep_State is System.Random_Numbers.State;
54 function Rep_Random is
55 new Random_Discrete (Result_Subtype, Result_Subtype'First);
57 function Random (Gen : Generator) return Result_Subtype is
59 return Rep_Random (Gen.Rep);
66 G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
71 procedure Reset (Gen : Generator) is
72 G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
82 Save (Gen.Rep, State (To_State));
89 G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
91 Reset (G, From_State);
94 function Image (Of_State : State) return String is
96 return Image (Rep_State (Of_State));
99 function Value (Coded_State : String) return State is
103 Reset (G.Rep, Coded_State);
104 System.Random_Numbers.Save (G.Rep, S);
108 end Ada.Numerics.Discrete_Random;