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------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT RUN-TIME COMPONENTS                         --
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--                                                                          --
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--                 G N A T . D Y N A M I C _ H T A B L E S                  --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--                     Copyright (C) 1995-2010, AdaCore                     --
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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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--  Hash table searching routines
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--  This package contains two separate packages. The Simple_HTable package
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--  provides a very simple abstraction that associates one element to one
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--  key value and takes care of all allocations automatically using the heap.
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--  The Static_HTable package provides a more complex interface that allows
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--  complete control over allocation.
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--  This package provides a facility similar to that of GNAT.HTable, except
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--  that this package declares types that can be used to define dynamic
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--  instances of hash tables, while instantiations in GNAT.HTable creates a
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--  single instance of the hash table.
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--  Note that this interface should remain synchronized with those in
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--  GNAT.HTable to keep as much coherency as possible between these two
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--  related units.
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with Ada.Unchecked_Deallocation;
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package GNAT.Dynamic_HTables is
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   -------------------
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   -- Static_HTable --
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   -------------------
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   --  A low-level Hash-Table abstraction, not as easy to instantiate as
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   --  Simple_HTable but designed to allow complete control over the
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   --  allocation of necessary data structures. Particularly useful when
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   --  dynamic allocation is not desired. The model is that each Element
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   --  contains its own Key that can be retrieved by Get_Key. Furthermore,
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   --  Element provides a link that can be used by the HTable for linking
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   --  elements with same hash codes:
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   --       Element
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   --         +-------------------+
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   --         |       Key         |
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   --         +-------------------+
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   --         :    other data     :
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   --         +-------------------+
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   --         |     Next Elmt     |
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   --         +-------------------+
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   generic
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      type Header_Num is range <>;
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      --  An integer type indicating the number and range of hash headers
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      type Element (<>) is limited private;
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      --  The type of element to be stored
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      type Elmt_Ptr is private;
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      --  The type used to reference an element (will usually be an access
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      --  type, but could be some other form of type such as an integer type).
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      Null_Ptr : Elmt_Ptr;
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      --  The null value of the Elmt_Ptr type
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      with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
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      with function  Next     (E : Elmt_Ptr) return Elmt_Ptr;
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      --  The type must provide an internal link for the sake of the
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      --  staticness of the HTable.
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      type Key is limited private;
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      with function Get_Key (E : Elmt_Ptr) return Key;
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      with function Hash    (F : Key)      return Header_Num;
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      with function Equal   (F1, F2 : Key) return Boolean;
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   package Static_HTable is
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      type Instance is private;
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      Nil : constant Instance;
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      procedure Reset (T : in out Instance);
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      --  Resets the hash table by releasing all memory associated with
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      --  it. The hash table can safely be reused after this call. For the
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      --  most common case where Elmt_Ptr is an access type, and Null_Ptr is
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      --  null, this is only needed if the same table is reused in a new
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      --  context. If Elmt_Ptr is other than an access type, or Null_Ptr is
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      --  other than null, then Reset must be called before the first use of
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      --  the hash table.
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      procedure Set (T : in out Instance; E : Elmt_Ptr);
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      --  Insert the element pointer in the HTable
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      function Get (T : Instance; K : Key) return Elmt_Ptr;
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      --  Returns the latest inserted element pointer with the given Key
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      --  or null if none.
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      procedure Remove (T : Instance; K : Key);
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      --  Removes the latest inserted element pointer associated with the
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      --  given key if any, does nothing if none.
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      function Get_First (T : Instance) return Elmt_Ptr;
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      --  Returns Null_Ptr if the Htable is empty, otherwise returns one
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      --  non specified element. There is no guarantee that 2 calls to this
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      --  function will return the same element.
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      function Get_Next (T : Instance) return Elmt_Ptr;
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      --  Returns a non-specified element that has not been returned by the
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      --  same function since the last call to Get_First or Null_Ptr if
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      --  there is no such element or Get_First has never been called. If
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      --  there is no call to 'Set' in between Get_Next calls, all the
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      --  elements of the Htable will be traversed.
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   private
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      type Instance_Data;
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      type Instance is access all Instance_Data;
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      Nil : constant Instance := null;
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   end Static_HTable;
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   -------------------
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   -- Simple_HTable --
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   -------------------
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   --  A simple hash table abstraction, easy to instantiate, easy to use.
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   --  The table associates one element to one key with the procedure Set.
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   --  Get retrieves the Element stored for a given Key. The efficiency of
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   --  retrieval is function of the size of the Table parameterized by
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   --  Header_Num and the hashing function Hash.
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   generic
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      type Header_Num is range <>;
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      --  An integer type indicating the number and range of hash headers
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      type Element is private;
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      --  The type of element to be stored
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      No_Element : Element;
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      --  The object that is returned by Get when no element has been set for
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      --  a given key
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      type Key is private;
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      with function Hash  (F : Key)      return Header_Num;
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      with function Equal (F1, F2 : Key) return Boolean;
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   package Simple_HTable is
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      type Instance is private;
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      Nil : constant Instance;
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      procedure Set (T : in out Instance; K : Key; E : Element);
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      --  Associates an element with a given key. Overrides any previously
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      --  associated element.
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      procedure Reset (T : in out Instance);
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      --  Releases all memory associated with the table. The table can be
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      --  reused after this call (it is automatically allocated on the first
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      --  access to the table).
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      function Get (T : Instance; K : Key) return Element;
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      --  Returns the Element associated with a key or No_Element if the
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      --  given key has not associated element
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      procedure Remove (T : Instance; K : Key);
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      --  Removes the latest inserted element pointer associated with the
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      --  given key if any, does nothing if none.
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      function Get_First (T : Instance) return Element;
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      --  Returns No_Element if the Htable is empty, otherwise returns one
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      --  non specified element. There is no guarantee that two calls to this
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      --  function will return the same element, if the Htable has been
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      --  modified between the two calls.
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      function Get_Next (T : Instance) return Element;
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      --  Returns a non-specified element that has not been returned by the
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      --  same function since the last call to Get_First or No_Element if
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      --  there is no such element. If there is no call to 'Set' in between
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      --  Get_Next calls, all the elements of the Htable will be traversed.
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      --  To guarantee that all the elements of the Htable will be traversed,
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      --  no modification of the Htable (Set, Reset, Remove) should occur
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      --  between a call to Get_First and subsequent consecutive calls to
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      --  Get_Next, until one of these calls returns No_Element.
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   private
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      type Element_Wrapper;
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      type Elmt_Ptr is access all Element_Wrapper;
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      type Element_Wrapper is record
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         K    : Key;
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         E    : Element;
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         Next : Elmt_Ptr;
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      end record;
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      procedure Free is new
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        Ada.Unchecked_Deallocation (Element_Wrapper, Elmt_Ptr);
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      procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
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      function  Next     (E : Elmt_Ptr) return Elmt_Ptr;
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      function  Get_Key  (E : Elmt_Ptr) return Key;
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      package Tab is new Static_HTable
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        (Header_Num => Header_Num,
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         Element    => Element_Wrapper,
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         Elmt_Ptr   => Elmt_Ptr,
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         Null_Ptr   => null,
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         Set_Next   => Set_Next,
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         Next       => Next,
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         Key        => Key,
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         Get_Key    => Get_Key,
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         Hash       => Hash,
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         Equal      => Equal);
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      type Instance is new Tab.Instance;
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      Nil : constant Instance := Instance (Tab.Nil);
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   end Simple_HTable;
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end GNAT.Dynamic_HTables;

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