| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT RUN-TIME COMPONENTS -- |
| -- -- |
| -- S Y S T E M . H T A B L E -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 1995-2022, 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. |
| |
| 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; |
