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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) 2007-2018, 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 --
-- <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.
-- 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;
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