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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) 1995-2013, 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 3, 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. --
+-- --
+-- As a special exception under Section 7 of GPL version 3, you are granted --
+-- additional permissions described in the GCC Runtime Library Exception, --
+-- version 3.1, as published by the Free Software Foundation. --
+-- --
+-- You should have received a copy of the GNU General Public License and --
+-- a copy of the GCC Runtime Library Exception along with this program; --
+-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
+-- <http://www.gnu.org/licenses/>. --
+-- --
+-- GNAT was originally developed by the GNAT team at New York University. --
+-- Extensive contributions were provided by Ada Core Technologies Inc. --
+-- --
+------------------------------------------------------------------------------
+
+-- 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_Warning;
+
+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 no 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.
+
+ procedure Get_First (K : in out Key; E : out Element);
+ -- This version of the iterator returns a key/element pair. A non-
+ -- specified entry is returned, and there is no guarantee that two
+ -- calls to this procedure will return the same element. If the table
+ -- is empty, E is set to No_Element, and K is unchanged, otherwise
+ -- K and E are set to the first returned entry.
+
+ procedure Get_Next (K : in out Key; E : out Element);
+ -- This version of the iterator returns a key/element pair. It returns
+ -- a non-specified element that has not been returned since the last
+ -- call to Get_First. If there is no remaining element, then E is set
+ -- to No_Element, and the value in K is unchanged, otherwise K and E
+ -- are set to the next entry. 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.
+
+ function Present (K : Key) return Boolean;
+ -- True if an element whose Get_Key is K is in the table
+
+ function Set_If_Not_Present (E : Elmt_Ptr) return Boolean;
+ -- If Present (Get_Key (E)), returns False. Otherwise, does Set (E), and
+ -- then returns True. Present (Get_Key (E)) is always True afterward,
+ -- and the result True indicates E is newly Set.
+
+ 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;