------------------------------------------------------------------------------ -- -- -- GNAT RUN-TIME COMPONENTS -- -- -- -- S Y S T E M . H T A B L E -- -- -- -- S p e c -- -- -- -- Copyright (C) 1995-2024, 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 -- -- . -- -- -- -- 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. 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;