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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- G N A T . M B B S _ D I S C R E T E _ R A N D O M --
-- --
-- S p e c --
-- --
-- Copyright (C) 1992-2010, Free Software Foundation, Inc. --
-- --
-- This specification is derived from the Ada Reference Manual for use with --
-- GNAT. The copyright notice above, and the license provisions that follow --
-- apply solely to the contents of the part following the private keyword. --
-- --
-- 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. --
-- --
------------------------------------------------------------------------------
-- The implementation used in this package was contributed by Robert
-- Eachus. It is based on the work of L. Blum, M. Blum, and M. Shub, SIAM
-- Journal of Computing, Vol 15. No 2, May 1986. The particular choices for P
-- and Q chosen here guarantee a period of 562,085,314,430,582 (about 2**49),
-- and the generated sequence has excellent randomness properties. For further
-- details, see the paper "Fast Generation of Trustworthy Random Numbers", by
-- Robert Eachus, which describes both the algorithm and the efficient
-- implementation approach used here.
-- Formerly, this package was Ada.Numerics.Discrete_Random. It is retained
-- here in part to allow users to reconstruct number sequences generated
-- by previous versions.
with Interfaces;
generic
type Result_Subtype is (<>);
package GNAT.MBBS_Discrete_Random is
-- The algorithm used here is reliable from a required statistical point of
-- view only up to 48 bits. We try to behave reasonably in the case of
-- larger types, but we can't guarantee the required properties. So
-- generate a warning for these (slightly) dubious cases.
pragma Compile_Time_Warning
(Result_Subtype'Size > 48,
"statistical properties not guaranteed for size > 48");
-- Basic facilities
type Generator is limited private;
function Random (Gen : Generator) return Result_Subtype;
procedure Reset (Gen : Generator);
procedure Reset (Gen : Generator; Initiator : Integer);
-- Advanced facilities
type State is private;
procedure Save (Gen : Generator; To_State : out State);
procedure Reset (Gen : Generator; From_State : State);
Max_Image_Width : constant := 80;
function Image (Of_State : State) return String;
function Value (Coded_State : String) return State;
private
subtype Int is Interfaces.Integer_32;
subtype Rst is Result_Subtype;
-- We prefer to use 14 digits for Flt, but some targets are more limited
type Flt is digits Positive'Min (14, Long_Long_Float'Digits);
RstF : constant Flt := Flt (Rst'Pos (Rst'First));
RstL : constant Flt := Flt (Rst'Pos (Rst'Last));
Offs : constant Flt := RstF - 0.5;
K1 : constant := 94_833_359;
K1F : constant := 94_833_359.0;
K2 : constant := 47_416_679;
K2F : constant := 47_416_679.0;
Scal : constant Flt := (RstL - RstF + 1.0) / (K1F * K2F);
type State is record
X1 : Int := Int (2999 ** 2);
X2 : Int := Int (1439 ** 2);
P : Int := K1;
Q : Int := K2;
FP : Flt := K1F;
Scl : Flt := Scal;
end record;
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
Gen_State : State;
end record;
end GNAT.MBBS_Discrete_Random;
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