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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                 G N A T . D Y N A M I C _ H T A B L E S                  --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                     Copyright (C) 1995-2008, 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.

--  This package provides a facility similar to that of GNAT.HTable, except

--  that this package declares types that can be used to define dynamic

--  instances of hash tables, while instantiations in GNAT.HTable creates a

--  single instance of the hash table.

--  Note that this interface should remain synchronized with those in

--  GNAT.HTable to keep as much coherency as possible between these two

--  related units.

with Ada.Unchecked_Deallocation;

package GNAT.Dynamic_HTables is

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

   -- 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

      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

      type Instance is private;

      Nil : constant Instance;

      procedure Reset (T : in out Instance);

      --  Resets the hash table by releasing all memory associated with

      --  it. The hash table can safely be reused after this call. 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 (T : in out Instance; E : Elmt_Ptr);

      --  Insert the element pointer in the HTable

      function Get (T : Instance; K : Key) return Elmt_Ptr;

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

      --  or null if none.

      procedure Remove (T : Instance; K : Key);

      --  Removes the latest inserted element pointer associated with the

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

      function Get_First (T : Instance) return Elmt_Ptr;

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

      --  non specified element. There is no guarantee that 2 calls to this

      --  function will return the same element.

      function Get_Next (T : Instance) 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.

   private

      type Instance_Data;

      type Instance is access all Instance_Data;

      Nil : constant Instance := null;

   end Static_HTable;

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

   -- 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

      type Instance is private;

      Nil : constant Instance;

      procedure Set (T : in out Instance; K : Key; E : Element);

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

      --  associated element.

      procedure Reset (T : in out Instance);

      --  Releases all memory associated with the table. The table can be

      --  reused after this call (it is automatically allocated on the first

      --  access to the table).

      function Get (T : Instance; K : Key) return Element;

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

      --  given key has not associated element

      procedure Remove (T : Instance; K : Key);

      --  Removes the latest inserted element pointer associated with the

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

      function Get_First (T : Instance) 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, if the Htable has been

      --  modified between the two calls.

      function Get_Next (T : Instance) 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.

      --  To guarantee that all the elements of the Htable will be traversed,

      --  no modification of the Htable (Set, Reset, Remove) should occur

      --  between a call to Get_First and subsequent consecutive calls to

      --  Get_Next, until one of these calls returns No_Element.

   private

      type Element_Wrapper;

      type Elmt_Ptr is access all Element_Wrapper;

      type Element_Wrapper is record

         K    : Key;

         E    : Element;

         Next : Elmt_Ptr;

      end record;

      procedure Free is new

        Ada.Unchecked_Deallocation (Element_Wrapper, Elmt_Ptr);

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

      function  Next     (E : Elmt_Ptr) return Elmt_Ptr;

      function  Get_Key  (E : Elmt_Ptr) return Key;

      package Tab is new Static_HTable

        (Header_Num => Header_Num,

         Element    => Element_Wrapper,

         Elmt_Ptr   => Elmt_Ptr,

         Null_Ptr   => null,

         Set_Next   => Set_Next,

         Next       => Next,

         Key        => Key,

         Get_Key    => Get_Key,

         Hash       => Hash,

         Equal      => Equal);

      type Instance is new Tab.Instance;

      Nil : constant Instance := Instance (Tab.Nil);

   end Simple_HTable;

end GNAT.Dynamic_HTables;