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Subject: Re: Question: re Image Files.
From: Shark8 <onewingedshark@gmail.com>
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Date: 2012-08-31T15:09:25-07:00
List-Id: <comp.lang.ada>

Here's one for you then. It builds a shuffled array over the given type, which can be used to index into something like a deck of cards or somesuch.

Generic
    Type Element is (<>);
    Low  : Natural:= Element'Pos(Element'First);
    High : Natural:= Element'Pos(Element'Last);
Package Random is
    SubType Element_Range is Integer Range Low..High;
    Function Incrementor Return Element;
    Type Element_Array is Array(Element_Range) of Element;

    Values : Element_Array;
    Procedure Print;
End Random;

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

With
	Ada.Text_IO,
	Ada.Numerics.Discrete_Random;

Use
	Ada.Text_IO;

Package Body Random is
    Count : Element := Element'First;

    Function To_Integer( Input : in Element ) Return Element_Range is
    begin
	Return Low;
    end;
    
    
    Function Incrementor Return Element is
    begin
	Return Result : Element:= Count do
	    Null;
	    Count:= Element'Succ( Result );
	Exception
	    When Constraint_Error => Count:= Element'First;
	End Return;
    end Incrementor;

    Procedure Swap( Index_1, Index_2 : In Integer ) is
	Temp : Constant Element:= Values( Integer(Index_1) );
    begin
	Values( Integer(Index_1) ):= Values( Integer(Index_2) );
	Values( Integer(Index_2) ):= Temp;
    end Swap;

    Procedure Print is
    begin
	Put_Line( "Length: " & Values'Length'Img );
	Put( "(" );
	For Index in Values'First..Integer'Pred(Values'Last) loop
	    Put( Values(Index)'Img & ',' );
	end loop;
	Put( Values(Values'Last)'Img );
	Put_Line( ")" );
    end Print;


Begin
    null;
    Shuffle:
    Declare
	Package Random_Element is New
	  Ada.Numerics.Discrete_Random( Element_Range );
	Number : Random_Element.Generator;
	Use Random_Element;
	Function Random( Gen : Generator ) Return Element_Range
		 Renames Random_Element.Random;
    Begin
	Reset( Number );
	Values:= Element_Array'( Others => Incrementor );
	       For Index in Element_Array'Range loop
	          Swap( Index, Random(Number) );
	       end loop;
    End Shuffle;
End Random;