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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                S Y S T E M . R A N D O M _ N U M B E R S                 --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 2007,2009  Free Software Foundation, Inc.         --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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--  Extended pseudo-random number generation

--  This package provides a type representing pseudo-random number generators,

--  and subprograms to extract various uniform distributions of numbers

--  from them. It also provides types for representing initialization values

--  and snapshots of internal generator state, which permit reproducible

--  pseudo-random streams.

--  The generator currently provided by this package has an extremely long

--  period (at least 2**19937-1), and passes the Big Crush test suite, with the

--  exception of the two linear complexity tests. Therefore, it is suitable

--  for simulations, but should not be used as a cryptographic pseudo-random

--  source without additional processing.

--  Note: this package is in the System hierarchy so that it can be directly

--  used by other predefined packages. User access to this package is via

--  the package GNAT.Random_Numbers (file g-rannum.ads), which also extends

--  its capabilities. The interfaces are different so as to include in

--  System.Random_Numbers only the definitions necessary to implement the

--  standard random-number packages Ada.Numerics.Float_Random and

--  Ada.Numerics.Discrete_Random.

with Interfaces;

package System.Random_Numbers is

   type Generator is limited private;

   type State is private;

   --  A non-limited version of a Generator's internal state

   function Random (Gen : Generator) return Float;

   function Random (Gen : Generator) return Long_Float;

   --  Return pseudo-random numbers uniformly distributed on [0 .. 1)

   function Random (Gen : Generator) return Interfaces.Unsigned_32;

   function Random (Gen : Generator) return Interfaces.Unsigned_64;

   --  Return pseudo-random numbers uniformly distributed on T'First .. T'Last

   --  for builtin integer types.

   generic

      type Result_Subtype is (<>);

      Default_Min : Result_Subtype := Result_Subtype'Val (0);

   function Random_Discrete

     (Gen : Generator;

      Min : Result_Subtype := Default_Min;

      Max : Result_Subtype := Result_Subtype'Last) return Result_Subtype;

   --  Returns pseudo-random numbers uniformly distributed on Min .. Max

   generic

      type Result_Subtype is digits <>;

   function Random_Float (Gen : Generator) return Result_Subtype;

   --  Returns pseudo-random numbers uniformly distributed on [0 .. 1)

   type Initialization_Vector is

     array (Integer range <>) of Interfaces.Unsigned_32;

   --  Provides the most general initialization values for a generator (used

   --  in Reset).  In general, there is little point in providing more than

   --  a certain number of values (currently 624).

   procedure Reset (Gen : out Generator);

   --  Re-initialize the state of Gen from the time of day

   procedure Reset (Gen : out Generator; Initiator : Initialization_Vector);

   procedure Reset (Gen : out Generator; Initiator : Interfaces.Integer_32);

   procedure Reset (Gen : out Generator; Initiator : Interfaces.Unsigned_32);

   procedure Reset (Gen : out Generator; Initiator : Integer);

   --  Re-initialize Gen based on the Initiator in various ways. Identical

   --  values of Initiator cause identical sequences of values.

   procedure Reset (Gen : out Generator; From_State : Generator);

   --  Causes the state of Gen to be identical to that of From_State; Gen

   --  and From_State will produce identical sequences of values subsequently.

   procedure Reset (Gen : out Generator; From_State : State);

   procedure Save  (Gen : Generator; To_State : out State);

   --  The sequence

   --     Save (Gen2, S); Reset (Gen1, S)

   --  has the same effect as Reset (Gen2, Gen1).

   procedure Reset (Gen : out Generator; From_Image : String);

   function Image (Gen : Generator) return String;

   --  The call

   --     Reset (Gen2, Image (Gen1))

   --  has the same effect as Reset (Gen2, Gen1);

   Max_Image_Width : constant := 11 * 624;

   --  Maximum possible length of result of Image (...)

   function Image (Of_State : State) return String;

   --  A String representation of Of_State. Identical to the result of

   --  Image (Gen), if Of_State has been set with Save (Gen, Of_State).

   function Value (Coded_State : String) return State;

   --  Inverse of Image on States

private

   N : constant := 624;

   --  The number of 32-bit integers in the shift register

   M : constant := 397;

   --  Feedback distance from the current position

   subtype State_Val is Interfaces.Unsigned_32;

   type State is array (0 .. N - 1) of State_Val;

   type Generator is limited record

      S : State := (others => 0);

      --  The shift register, a circular buffer

      I : Integer := N;

      --  Current starting position in shift register S

   end record;

end System.Random_Numbers;