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1 706 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT RUN-TIME COMPONENTS                         --
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--                                                                          --
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--            G N A T . M B B S _ D I S C R E T E _ R A N D O M             --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--          Copyright (C) 1992-2010, Free Software Foundation, Inc.         --
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--                                                                          --
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-- This specification is derived from the Ada Reference Manual for use with --
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-- GNAT. The copyright notice above, and the license provisions that follow --
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-- apply solely to the  contents of the part following the private keyword. --
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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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--  The implementation used in this package was contributed by Robert
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--  Eachus. It is based on the work of L. Blum, M. Blum, and M. Shub, SIAM
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--  Journal of Computing, Vol 15. No 2, May 1986. The particular choices for P
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--  and Q chosen here guarantee a period of 562,085,314,430,582 (about 2**49),
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--  and the generated sequence has excellent randomness properties. For further
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--  details, see the paper "Fast Generation of Trustworthy Random Numbers", by
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--  Robert Eachus, which describes both the algorithm and the efficient
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--  implementation approach used here.
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--  Formerly, this package was Ada.Numerics.Discrete_Random. It is retained
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--  here in part to allow users to reconstruct number sequences generated
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--  by previous versions.
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with Interfaces;
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generic
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   type Result_Subtype is (<>);
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package GNAT.MBBS_Discrete_Random is
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   --  The algorithm used here is reliable from a required statistical point of
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   --  view only up to 48 bits. We try to behave reasonably in the case of
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   --  larger types, but we can't guarantee the required properties. So
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   --  generate a warning for these (slightly) dubious cases.
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   pragma Compile_Time_Warning
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     (Result_Subtype'Size > 48,
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      "statistical properties not guaranteed for size > 48");
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   --  Basic facilities
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   type Generator is limited private;
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   function Random (Gen : Generator) return Result_Subtype;
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   procedure Reset (Gen : Generator);
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   procedure Reset (Gen : Generator; Initiator : Integer);
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   --  Advanced facilities
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   type State is private;
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   procedure Save  (Gen : Generator; To_State   : out State);
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   procedure Reset (Gen : Generator; From_State : State);
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   Max_Image_Width : constant := 80;
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   function Image (Of_State    : State)  return String;
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   function Value (Coded_State : String) return State;
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private
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   subtype Int is Interfaces.Integer_32;
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   subtype Rst is Result_Subtype;
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   --  We prefer to use 14 digits for Flt, but some targets are more limited
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   type Flt is digits Positive'Min (14, Long_Long_Float'Digits);
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   RstF : constant Flt := Flt (Rst'Pos (Rst'First));
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   RstL : constant Flt := Flt (Rst'Pos (Rst'Last));
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   Offs : constant Flt := RstF - 0.5;
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   K1   : constant := 94_833_359;
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   K1F  : constant := 94_833_359.0;
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   K2   : constant := 47_416_679;
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   K2F  : constant := 47_416_679.0;
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   Scal : constant Flt := (RstL - RstF + 1.0) / (K1F * K2F);
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   type State is record
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      X1  : Int := Int (2999 ** 2);
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      X2  : Int := Int (1439 ** 2);
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      P   : Int := K1;
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      Q   : Int := K2;
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      FP  : Flt := K1F;
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      Scl : Flt := Scal;
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   end record;
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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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      Gen_State : State;
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   end record;
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end GNAT.MBBS_Discrete_Random;

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