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) 2007-2015, 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 uniform distributions of numbers
  36 --  from them. It also provides types for representing initialization values
  37 --  and snapshots of internal generator state, which permit reproducible
  38 --  pseudo-random streams.
  39
  40 --  The generator currently provided by this package has an extremely long
  41 --  period (at least 2**19937-1), and passes the Big Crush test suite, with the
  42 --  exception of the two linear complexity tests. Therefore, it is suitable
  43 --  for simulations, but should not be used as a cryptographic pseudo-random
  44 --  source without additional processing.
  45
  46 --  Note: this package is in the System hierarchy so that it can be directly
  47 --  used by other predefined packages. User access to this package is via
  48 --  the package GNAT.Random_Numbers (file g-rannum.ads), which also extends
  49 --  its capabilities. The interfaces are different so as to include in
  50 --  System.Random_Numbers only the definitions necessary to implement the
  51 --  standard random-number packages Ada.Numerics.Float_Random and
  52 --  Ada.Numerics.Discrete_Random.
  53
  54 --  Note: this package is marked SPARK_Mode Off, because functions Random work
  55 --  by side-effect to change the value of the generator, hence they should not
  56 --  be called from SPARK code.
  57
  58 with Interfaces;
  59
  60 package System.Random_Numbers with
  61   SPARK_Mode => Off
  62 is
  63    type Generator is limited private;
  64    --  Generator encodes the current state of a random number stream, it is
  65    --  provided as input to produce the next random number, and updated so
  66    --  that it is ready to produce the next one.
  67
  68    type State is private;
  69    --  A non-limited version of a Generator's internal state
  70
  71    function Random (Gen : Generator) return Float;
  72    function Random (Gen : Generator) return Long_Float;
  73    --  Return pseudo-random numbers uniformly distributed on [0.0 .. 1.0)
  74
  75    function Random (Gen : Generator) return Interfaces.Unsigned_32;
  76    function Random (Gen : Generator) return Interfaces.Unsigned_64;
  77    --  Return pseudo-random numbers uniformly distributed on T'First .. T'Last
  78    --  for builtin integer types.
  79
  80    generic
  81       type Result_Subtype is (<>);
  82       Default_Min : Result_Subtype := Result_Subtype'Val (0);
  83    function Random_Discrete
  84      (Gen : Generator;
  85       Min : Result_Subtype := Default_Min;
  86       Max : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
  87    --  Returns pseudo-random numbers uniformly distributed on Min .. Max
  88
  89    generic
  90       type Result_Subtype is digits <>;
  91    function Random_Float (Gen : Generator) return Result_Subtype;
  92    --  Returns pseudo-random numbers uniformly distributed on [0 .. 1)
  93
  94    type Initialization_Vector is
  95      array (Integer range <>) of Interfaces.Unsigned_32;
  96    --  Provides the most general initialization values for a generator (used
  97    --  in Reset).  In general, there is little point in providing more than
  98    --  a certain number of values (currently 624).
  99
 100    procedure Reset (Gen : Generator);
 101    --  Re-initialize the state of Gen from the time of day
 102
 103    procedure Reset (Gen : Generator; Initiator : Initialization_Vector);
 104    procedure Reset (Gen : Generator; Initiator : Interfaces.Integer_32);
 105    procedure Reset (Gen : Generator; Initiator : Interfaces.Unsigned_32);
 106    procedure Reset (Gen : Generator; Initiator : Integer);
 107    --  Re-initialize Gen based on the Initiator in various ways. Identical
 108    --  values of Initiator cause identical sequences of values.
 109
 110    procedure Reset (Gen : Generator; From_State : Generator);
 111    --  Causes the state of Gen to be identical to that of From_State; Gen
 112    --  and From_State will produce identical sequences of values subsequently.
 113
 114    procedure Reset (Gen : Generator; From_State : State);
 115    procedure Save  (Gen : Generator; To_State : out State);
 116    --  The sequence
 117    --     Save (Gen2, S); Reset (Gen1, S)
 118    --  has the same effect as Reset (Gen2, Gen1).
 119
 120    procedure Reset (Gen : Generator; From_Image : String);
 121    function Image (Gen : Generator) return String;
 122    --  The call
 123    --     Reset (Gen2, Image (Gen1))
 124    --  has the same effect as Reset (Gen2, Gen1);
 125
 126    Max_Image_Width : constant := 11 * 624;
 127    --  Maximum possible length of result of Image (...)
 128
 129    function Image (Of_State : State) return String;
 130    --  A String representation of Of_State. Identical to the result of
 131    --  Image (Gen), if Of_State has been set with Save (Gen, Of_State).
 132
 133    function Value (Coded_State : String) return State;
 134    --  Inverse of Image on States
 135
 136 private
 137
 138    N : constant := 624;
 139    --  The number of 32-bit integers in the shift register
 140
 141    M : constant := 397;
 142    --  Feedback distance from the current position
 143
 144    subtype State_Val is Interfaces.Unsigned_32;
 145    type State is array (0 .. N - 1) of State_Val;
 146
 147    type Writable_Access (Self : access Generator) is limited null record;
 148    --  Auxiliary type to make Generator a self-referential type
 149
 150    type Generator is limited record
 151       Writable  : Writable_Access (Generator'Access);
 152       --  This self reference allows functions to modify Generator arguments
 153
 154       S : State := (others => 0);
 155       --  The shift register, a circular buffer
 156
 157       I : Integer := N;
 158       --  Current starting position in shift register S (N means uninitialized)
 159       --  We should avoid using the identifier I here ???
 160    end record;
 161
 162 end System.Random_Numbers;