------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUN-TIME COMPONENTS                         --
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--         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          --
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------------------------------------------------------------------------------

with System.Random_Numbers; use System.Random_Numbers;

package body Ada.Numerics.Discrete_Random is

   -------------------------
   -- Implementation Note --
   -------------------------

   --  The design of this spec is very awkward, as a result of Ada 95 not
   --  permitting in-out parameters for function formals (most naturally
   --  Generator values would be passed this way). In pure Ada 95, the only
   --  solution is to use the heap and pointers, and, to avoid memory leaks,
   --  controlled types.

   --  This is awfully heavy, so what we do is to use Unrestricted_Access to
   --  get a pointer to the state in the passed Generator. This works because
   --  Generator is a limited type and will thus always be passed by reference.

   subtype Rep_Generator is System.Random_Numbers.Generator;
   subtype Rep_State is System.Random_Numbers.State;

   function Rep_Random is
      new Random_Discrete (Result_Subtype, Result_Subtype'First);

   function Random (Gen : Generator) return Result_Subtype is
   begin
      return Rep_Random (Gen.Rep);
   end Random;

   procedure Reset
     (Gen       : Generator;
      Initiator : Integer)
   is
      G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
   begin
      Reset (G, Initiator);
   end Reset;

   procedure Reset (Gen : Generator) is
      G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
   begin
      Reset (G);
   end Reset;

   procedure Save
     (Gen        : Generator;
      To_State   : out State)
   is
   begin
      Save (Gen.Rep, State (To_State));
   end Save;

   procedure Reset
     (Gen        : Generator;
      From_State : State)
   is
      G : Rep_Generator renames Gen.Rep'Unrestricted_Access.all;
   begin
      Reset (G, From_State);
   end Reset;

   function Image (Of_State : State)  return String is
   begin
      return Image (Rep_State (Of_State));
   end Image;

   function Value (Coded_State : String) return State is
      G : Generator;
      S : Rep_State;
   begin
      Reset (G.Rep, Coded_State);
      System.Random_Numbers.Save (G.Rep, S);
      return State (S);
   end Value;

end Ada.Numerics.Discrete_Random;