Package Name: ada.numerics.discrete_random

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------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUNTIME COMPONENTS                          --
--                                                                          --
--         A D A . N U M E R I C S . D I S C R E T E _ R A N D O M          --
--                                                                          --
--                                 S p e c                                  --
--                                                                          --
--                            $Revision: 1.9 $                              --
--                                                                          --
-- This specification is adapted from the Ada Reference Manual for use with --
-- GNAT.  In accordance with the copyright of that document, you can freely --
-- copy and modify this specification,  provided that if you redistribute a --
-- modified version,  any changes that you have made are clearly indicated. --
--                                                                          --

------------------------------------------------------------------------------

with Interfaces;
generic

   type Result_Subtype is (<>);

package Ada.Numerics.Discrete_Random is

   --  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;

   type Flt is digits 14;
   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 Generator is limited record
      Gen_State : State;

   end record;
end Ada.Numerics.Discrete_Random;