gcc/ada/a-nudira.adb

   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 --                                 B o d y                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2010, 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 with System.Random_Numbers; use System.Random_Numbers;
  33
  34 package body Ada.Numerics.Discrete_Random is
  35
  36    -------------------------
  37    -- Implementation Note --
  38    -------------------------
  39
  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.
  46
  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.
  50
  51    subtype Rep_Generator is System.Random_Numbers.Generator;
  52    subtype Rep_State is System.Random_Numbers.State;
  53
  54    function Rep_Random is
  55       new Random_Discrete (Result_Subtype, Result_Subtype'First);
  56
  57    function Random (Gen : Generator) return Result_Subtype is
  58    begin
  59       return Rep_Random (Gen.Rep);
  60    end Random;
  61
  62    procedure Reset
  63      (Gen       : Generator;
  64       Initiator : Integer)
  65    is
  66       G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
  67    begin
  68       Reset (G, Initiator);
  69    end Reset;
  70
  71    procedure Reset (Gen : Generator) is
  72       G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
  73    begin
  74       Reset (G);
  75    end Reset;
  76
  77    procedure Save
  78      (Gen        : Generator;
  79       To_State   : out State)
  80    is
  81    begin
  82       Save (Gen.Rep, State (To_State));
  83    end Save;
  84
  85    procedure Reset
  86      (Gen        : Generator;
  87       From_State : State)
  88    is
  89       G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
  90    begin
  91       Reset (G, From_State);
  92    end Reset;
  93
  94    function Image (Of_State : State)  return String is
  95    begin
  96       return Image (Rep_State (Of_State));
  97    end Image;
  98
  99    function Value (Coded_State : String) return State is
 100       G : Generator;
 101       S : Rep_State;
 102    begin
 103       Reset (G.Rep, Coded_State);
 104       System.Random_Numbers.Save (G.Rep, S);
 105       return State (S);
 106    end Value;
 107
 108 end Ada.Numerics.Discrete_Random;