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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) 2007-2010, 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. --
+-- --
+------------------------------------------------------------------------------
+
+-- 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 : Generator);
+ -- Re-initialize the state of Gen from the time of day
+
+ procedure Reset (Gen : Generator; Initiator : Initialization_Vector);
+ procedure Reset (Gen : Generator; Initiator : Interfaces.Integer_32);
+ procedure Reset (Gen : Generator; Initiator : Interfaces.Unsigned_32);
+ procedure Reset (Gen : 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 : 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 : 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 : 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 Writable_Access (Self : access Generator) is limited null record;
+ -- Auxiliary type to make Generator a self-referential type
+
+ type Generator is limited record
+ Writable : Writable_Access (Generator'Access);
+ -- This self reference allows functions to modify Generator arguments
+
+ S : State := (others => 0);
+ -- The shift register, a circular buffer
+
+ I : Integer := N;
+ -- Current starting position in shift register S (N means uninitialized)
+ -- We should avoid using the identifier I here ???
+ end record;
+
+end System.Random_Numbers;