gcc/ada/s-rannum.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                S Y S T E M . R A N D O M _ N U M B E R S                 --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 2007, 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 2,  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.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  Extended pseudo-random number generation
  35
  36 --  This package provides a type representing pseudo-random number generators,
  37 --  and subprograms to extract various uniform distributions of numbers
  38 --  from them. It also provides types for representing initialization values
  39 --  and snapshots of internal generator state, which permit reproducible
  40 --  pseudo-random streams.
  41
  42 --  The generator currently provided by this package has an extremely long
  43 --  period (at least 2**19937-1), and passes the Big Crush test suite, with the
  44 --  exception of the two linear complexity tests. Therefore, it is suitable
  45 --  for simulations, but should not be used as a cryptographic pseudo-random
  46 --  source without additional processing.
  47
  48 --  Note: this package is in the System hierarchy so that it can be directly
  49 --  used by other predefined packages. User access to this package is via
  50 --  the package GNAT.Random_Numbers (file g-rannum.ads), which also extends
  51 --  its capabilities. The interfaces are different so as to include in
  52 --  System.Random_Numbers only the definitions necessary to implement the
  53 --  standard random-number packages Ada.Numerics.Float_Random and
  54 --  Ada.Numerics.Discrete_Random.
  55
  56 with Interfaces;
  57
  58 package System.Random_Numbers is
  59
  60    type Generator is limited private;
  61    type State is private;
  62    --  A non-limited version of a Generator's internal state
  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.Unsigned_32;
  69    function Random (Gen : Generator) return Interfaces.Unsigned_64;
  70    --  Return pseudo-random numbers uniformly distributed on T'First .. T'Last
  71    --  for builtin integer types.
  72
  73    generic
  74       type Result_Subtype is (<>);
  75       Default_Min : Result_Subtype := Result_Subtype'Val (0);
  76    function Random_Discrete
  77      (Gen : Generator;
  78       Min : Result_Subtype := Default_Min;
  79       Max : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
  80    --  Returns pseudo-random numbers uniformly distributed on Min .. Max
  81
  82    generic
  83       type Result_Subtype is digits <>;
  84    function Random_Float (Gen : Generator) return Result_Subtype;
  85    --  Returns pseudo-random numbers uniformly distributed on [0 .. 1)
  86
  87    type Initialization_Vector is
  88      array (Integer range <>) of Interfaces.Unsigned_32;
  89    --  Provides the most general initialization values for a generator (used
  90    --  in Reset).  In general, there is little point in providing more than
  91    --  a certain number of values (currently 624).
  92
  93    procedure Reset (Gen : out Generator);
  94    --  Re-initialize the state of Gen from the time of day
  95
  96    procedure Reset (Gen : out Generator; Initiator : Initialization_Vector);
  97    procedure Reset (Gen : out Generator; Initiator : Interfaces.Integer_32);
  98    procedure Reset (Gen : out Generator; Initiator : Interfaces.Unsigned_32);
  99    procedure Reset (Gen : out Generator; Initiator : Integer);
 100    --  Re-initialize Gen based on the Initiator in various ways. Identical
 101    --  values of Initiator cause identical sequences of values.
 102
 103    procedure Reset (Gen : out Generator; From_State : Generator);
 104    --  Causes the state of Gen to be identical to that of From_State; Gen
 105    --  and From_State will produce identical sequences of values subsequently.
 106
 107    procedure Reset (Gen : out Generator; From_State : State);
 108    procedure Save  (Gen : Generator; To_State : out State);
 109    --  The sequence
 110    --     Save (Gen2, S); Reset (Gen1, S)
 111    --  has the same effect as Reset (Gen2, Gen1).
 112
 113    procedure Reset (Gen : out Generator; From_Image : String);
 114    function Image (Gen : Generator) return String;
 115    --  The call
 116    --     Reset (Gen2, Image (Gen1))
 117    --  has the same effect as Reset (Gen2, Gen1);
 118
 119    Max_Image_Width : constant := 11 * 624;
 120    --  Maximum possible length of result of Image (...)
 121
 122    function Image (Of_State : State) return String;
 123    --  A String representation of Of_State. Identical to the result of
 124    --  Image (Gen), if Of_State has been set with Save (Gen, Of_State).
 125
 126    function Value (Coded_State : String) return State;
 127    --  Inverse of Image on States
 128
 129 private
 130
 131    N : constant := 624;
 132    --  The number of 32-bit integers in the shift register
 133
 134    M : constant := 397;
 135    --  Feedback distance from the current position
 136
 137    subtype State_Val is Interfaces.Unsigned_32;
 138    type State is array (0 .. N - 1) of State_Val;
 139
 140    type Generator is limited record
 141       S : State := (others => 0);
 142       --  The shift register, a circular buffer
 143
 144       I : Integer := N;
 145       --  Current starting position in shift register S
 146    end record;
 147
 148 end System.Random_Numbers;