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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                        S Y S T E M . H T A B L E                         --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                     Copyright (C) 1995-2009, AdaCore                     --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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--  Hash table searching routines

--  This package contains two separate packages. The Simple_HTable package

--  provides a very simple abstraction that associates one element to one

--  key value and takes care of all allocations automatically using the heap.

--  The Static_HTable package provides a more complex interface that allows

--  complete control over allocation.

pragma Compiler_Unit;

package System.HTable is

   pragma Preelaborate;

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

   -- Simple_HTable --

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

   --  A simple hash table abstraction, easy to instantiate, easy to use.

   --  The table associates one element to one key with the procedure Set.

   --  Get retrieves the Element stored for a given Key. The efficiency of

   --  retrieval is function of the size of the Table parameterized by

   --  Header_Num and the hashing function Hash.

   generic

      type Header_Num is range <>;

      --  An integer type indicating the number and range of hash headers

      type Element is private;

      --  The type of element to be stored

      No_Element : Element;

      --  The object that is returned by Get when no element has been set for

      --  a given key

      type Key is private;

      with function Hash  (F : Key)      return Header_Num;

      with function Equal (F1, F2 : Key) return Boolean;

   package Simple_HTable is

      procedure Set (K : Key; E : Element);

      --  Associates an element with a given key. Overrides any previously

      --  associated element.

      procedure Reset;

      --  Removes and frees all elements in the table

      function Get (K : Key) return Element;

      --  Returns the Element associated with a key or No_Element if the

      --  given key has not associated element

      procedure Remove (K : Key);

      --  Removes the latest inserted element pointer associated with the

      --  given key if any, does nothing if none.

      function Get_First return Element;

      --  Returns No_Element if the HTable is empty, otherwise returns one

      --  non specified element. There is no guarantee that two calls to this

      --  function will return the same element.

      function Get_Next return Element;

      --  Returns a non-specified element that has not been returned by the

      --  same function since the last call to Get_First or No_Element if

      --  there is no such element. If there is no call to 'Set' in between

      --  Get_Next calls, all the elements of the HTable will be traversed.

   end Simple_HTable;

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

   -- Static_HTable --

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

   --  A low-level Hash-Table abstraction, not as easy to instantiate as

   --  Simple_HTable but designed to allow complete control over the

   --  allocation of necessary data structures. Particularly useful when

   --  dynamic allocation is not desired. The model is that each Element

   --  contains its own Key that can be retrieved by Get_Key. Furthermore,

   --  Element provides a link that can be used by the HTable for linking

   --  elements with same hash codes:

   --       Element

   --         +-------------------+

   --         |       Key         |

   --         +-------------------+

   --         :    other data     :

   --         +-------------------+

   --         |     Next Elmt     |

   --         +-------------------+

   generic

      type Header_Num is range <>;

      --  An integer type indicating the number and range of hash headers

      type Element (<>) is limited private;

      --  The type of element to be stored. This is historically part of the

      --  interface, even though it is not used at all in the operations of

      --  the package.

      pragma Warnings (Off, Element);

      --  We have to kill warnings here, because Element is and always

      --  has been unreferenced, but we cannot remove it at this stage,

      --  since this unit is in wide use, and it certainly seems harmless.

      type Elmt_Ptr is private;

      --  The type used to reference an element (will usually be an access

      --  type, but could be some other form of type such as an integer type).

      Null_Ptr : Elmt_Ptr;

      --  The null value of the Elmt_Ptr type

      with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);

      with function  Next     (E : Elmt_Ptr) return Elmt_Ptr;

      --  The type must provide an internal link for the sake of the

      --  staticness of the HTable.

      type Key is limited private;

      with function Get_Key (E : Elmt_Ptr) return Key;

      with function Hash    (F : Key)      return Header_Num;

      with function Equal   (F1, F2 : Key) return Boolean;

   package Static_HTable is

      procedure Reset;

      --  Resets the hash table by setting all its elements to Null_Ptr. The

      --  effect is to clear the hash table so that it can be reused. For the

      --  most common case where Elmt_Ptr is an access type, and Null_Ptr is

      --  null, this is only needed if the same table is reused in a new

      --  context. If Elmt_Ptr is other than an access type, or Null_Ptr is

      --  other than null, then Reset must be called before the first use

      --  of the hash table.

      procedure Set (E : Elmt_Ptr);

      --  Insert the element pointer in the HTable

      function Get (K : Key) return Elmt_Ptr;

      --  Returns the latest inserted element pointer with the given Key

      --  or null if none.

      procedure Remove (K : Key);

      --  Removes the latest inserted element pointer associated with the

      --  given key if any, does nothing if none.

      function Get_First return Elmt_Ptr;

      --  Returns Null_Ptr if the HTable is empty, otherwise returns one

      --  non specified element. There is no guarantee that two calls to this

      --  function will return the same element.

      function Get_Next return Elmt_Ptr;

      --  Returns a non-specified element that has not been returned by the

      --  same function since the last call to Get_First or Null_Ptr if

      --  there is no such element or Get_First has never been called. If

      --  there is no call to 'Set' in between Get_Next calls, all the

      --  elements of the HTable will be traversed.

   end Static_HTable;

   ----------

   -- Hash --

   ----------

   --  A generic hashing function working on String keys

   generic

      type Header_Num is range <>;

   function Hash (Key : String) return Header_Num;

end System.HTable;