163 lines
7.7 KiB
Ada
163 lines
7.7 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME COMPONENTS --
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-- --
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-- S Y S T E M . R A N D O M _ N U M B E R S --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 2007-2015, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- Extended pseudo-random number generation
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-- This package provides a type representing pseudo-random number generators,
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-- and subprograms to extract various uniform distributions of numbers
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-- from them. It also provides types for representing initialization values
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-- and snapshots of internal generator state, which permit reproducible
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-- pseudo-random streams.
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-- The generator currently provided by this package has an extremely long
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-- period (at least 2**19937-1), and passes the Big Crush test suite, with the
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-- exception of the two linear complexity tests. Therefore, it is suitable
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-- for simulations, but should not be used as a cryptographic pseudo-random
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-- source without additional processing.
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-- Note: this package is in the System hierarchy so that it can be directly
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-- used by other predefined packages. User access to this package is via
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-- the package GNAT.Random_Numbers (file g-rannum.ads), which also extends
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-- its capabilities. The interfaces are different so as to include in
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-- System.Random_Numbers only the definitions necessary to implement the
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-- standard random-number packages Ada.Numerics.Float_Random and
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-- Ada.Numerics.Discrete_Random.
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-- Note: this package is marked SPARK_Mode Off, because functions Random work
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-- by side-effect to change the value of the generator, hence they should not
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-- be called from SPARK code.
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with Interfaces;
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package System.Random_Numbers with
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SPARK_Mode => Off
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is
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type Generator is limited private;
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-- Generator encodes the current state of a random number stream, it is
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-- provided as input to produce the next random number, and updated so
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-- that it is ready to produce the next one.
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type State is private;
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-- A non-limited version of a Generator's internal state
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function Random (Gen : Generator) return Float;
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function Random (Gen : Generator) return Long_Float;
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-- Return pseudo-random numbers uniformly distributed on [0.0 .. 1.0)
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function Random (Gen : Generator) return Interfaces.Unsigned_32;
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function Random (Gen : Generator) return Interfaces.Unsigned_64;
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-- Return pseudo-random numbers uniformly distributed on T'First .. T'Last
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-- for builtin integer types.
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generic
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type Result_Subtype is (<>);
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Default_Min : Result_Subtype := Result_Subtype'Val (0);
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function Random_Discrete
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(Gen : Generator;
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Min : Result_Subtype := Default_Min;
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Max : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
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-- Returns pseudo-random numbers uniformly distributed on Min .. Max
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generic
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type Result_Subtype is digits <>;
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function Random_Float (Gen : Generator) return Result_Subtype;
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-- Returns pseudo-random numbers uniformly distributed on [0 .. 1)
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type Initialization_Vector is
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array (Integer range <>) of Interfaces.Unsigned_32;
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-- Provides the most general initialization values for a generator (used
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-- in Reset). In general, there is little point in providing more than
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-- a certain number of values (currently 624).
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procedure Reset (Gen : Generator);
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-- Re-initialize the state of Gen from the time of day
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procedure Reset (Gen : Generator; Initiator : Initialization_Vector);
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procedure Reset (Gen : Generator; Initiator : Interfaces.Integer_32);
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procedure Reset (Gen : Generator; Initiator : Interfaces.Unsigned_32);
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procedure Reset (Gen : Generator; Initiator : Integer);
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-- Re-initialize Gen based on the Initiator in various ways. Identical
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-- values of Initiator cause identical sequences of values.
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procedure Reset (Gen : Generator; From_State : Generator);
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-- Causes the state of Gen to be identical to that of From_State; Gen
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-- and From_State will produce identical sequences of values subsequently.
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procedure Reset (Gen : Generator; From_State : State);
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procedure Save (Gen : Generator; To_State : out State);
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-- The sequence
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-- Save (Gen2, S); Reset (Gen1, S)
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-- has the same effect as Reset (Gen2, Gen1).
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procedure Reset (Gen : Generator; From_Image : String);
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function Image (Gen : Generator) return String;
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-- The call
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-- Reset (Gen2, Image (Gen1))
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-- has the same effect as Reset (Gen2, Gen1);
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Max_Image_Width : constant := 11 * 624;
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-- Maximum possible length of result of Image (...)
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function Image (Of_State : State) return String;
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-- A String representation of Of_State. Identical to the result of
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-- Image (Gen), if Of_State has been set with Save (Gen, Of_State).
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function Value (Coded_State : String) return State;
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-- Inverse of Image on States
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private
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N : constant := 624;
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-- The number of 32-bit integers in the shift register
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M : constant := 397;
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-- Feedback distance from the current position
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subtype State_Val is Interfaces.Unsigned_32;
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type State is array (0 .. N - 1) of State_Val;
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type Writable_Access (Self : access Generator) is limited null record;
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-- Auxiliary type to make Generator a self-referential type
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type Generator is limited record
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Writable : Writable_Access (Generator'Access);
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-- This self reference allows functions to modify Generator arguments
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S : State := (others => 0);
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-- The shift register, a circular buffer
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I : Integer := N;
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-- Current starting position in shift register S (N means uninitialized)
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-- We should avoid using the identifier I here ???
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end record;
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end System.Random_Numbers;
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