------------------------------------------------------------------------------ -- -- -- 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) 2007-2018, 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 -- -- . -- -- -- -- 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. -- Note: this package is marked SPARK_Mode Off, because functions Random work -- by side-effect to change the value of the generator, hence they should not -- be called from SPARK code. with Interfaces; package System.Random_Numbers with SPARK_Mode => Off is type Generator is limited private; -- Generator encodes the current state of a random number stream, it is -- provided as input to produce the next random number, and updated so -- that it is ready to produce the next one. 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 [0.0 .. 1.0) 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;