1 ------------------------------------------------------------------------------
3 -- GNAT RUNTIME COMPONENTS --
5 -- G N A T . H T A B L E --
11 -- Copyright (C) 1995-2001 Ada Core Technologies, Inc. --
13 -- GNAT is free software; you can redistribute it and/or modify it under --
14 -- terms of the GNU General Public License as published by the Free Soft- --
15 -- ware Foundation; either version 2, or (at your option) any later ver- --
16 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
17 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
18 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
19 -- for more details. You should have received a copy of the GNU General --
20 -- Public License distributed with GNAT; see file COPYING. If not, write --
21 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
22 -- MA 02111-1307, USA. --
24 -- As a special exception, if other files instantiate generics from this --
25 -- unit, or you link this unit with other files to produce an executable, --
26 -- this unit does not by itself cause the resulting executable to be --
27 -- covered by the GNU General Public License. This exception does not --
28 -- however invalidate any other reasons why the executable file might be --
29 -- covered by the GNU Public License. --
31 -- GNAT is maintained by Ada Core Technologies Inc (http://www.gnat.com). --
33 ------------------------------------------------------------------------------
35 -- Hash table searching routines
37 -- This package contains two separate packages. The Simple_Htable package
38 -- provides a very simple abstraction that asosicates one element to one
39 -- key values and takes care of all allocation automatically using the heap.
40 -- The Static_Htable package provides a more complex interface that allows
41 -- complete control over allocation.
43 package GNAT.HTable is
44 pragma Preelaborate (HTable);
50 -- A simple hash table abstraction, easy to instantiate, easy to use.
51 -- The table associates one element to one key with the procedure Set.
52 -- Get retrieves the Element stored for a given Key. The efficiency of
53 -- retrieval is function of the size of the Table parameterized by
54 -- Header_Num and the hashing function Hash.
57 type Header_Num is range <>;
58 -- An integer type indicating the number and range of hash headers.
60 type Element is private;
61 -- The type of element to be stored
64 -- The object that is returned by Get when no element has been set for
68 with function Hash (F : Key) return Header_Num;
69 with function Equal (F1, F2 : Key) return Boolean;
71 package Simple_HTable is
73 procedure Set (K : Key; E : Element);
74 -- Associates an element with a given key. Overrides any previously
75 -- associated element.
78 -- Removes and frees all elements in the table
80 function Get (K : Key) return Element;
81 -- Returns the Element associated with a key or No_Element if the
82 -- given key has not associated element
84 procedure Remove (K : Key);
85 -- Removes the latest inserted element pointer associated with the
86 -- given key if any, does nothing if none.
88 function Get_First return Element;
89 -- Returns No_Element if the Htable is empty, otherwise returns one
90 -- non specified element. There is no guarantee that 2 calls to this
91 -- function will return the same element.
93 function Get_Next return Element;
94 -- Returns a non-specified element that has not been returned by the
95 -- same function since the last call to Get_First or No_Element if
96 -- there is no such element. If there is no call to 'Set' in between
97 -- Get_Next calls, all the elements of the Htable will be traversed.
104 -- A low-level Hash-Table abstraction, not as easy to instantiate as
105 -- Simple_HTable but designed to allow complete control over the
106 -- allocation of necessary data structures. Particularly useful when
107 -- dynamic allocation is not desired. The model is that each Element
108 -- contains its own Key that can be retrieved by Get_Key. Furthermore,
109 -- Element provides a link that can be used by the HTable for linking
110 -- elements with same hash codes:
114 -- +-------------------+
116 -- +-------------------+
118 -- +-------------------+
120 -- +-------------------+
123 type Header_Num is range <>;
124 -- An integer type indicating the number and range of hash headers.
126 type Element (<>) is limited private;
127 -- The type of element to be stored
129 type Elmt_Ptr is private;
130 -- The type used to reference an element (will usually be an access
131 -- type, but could be some other form of type such as an integer type).
134 -- The null value of the Elmt_Ptr type.
136 with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
137 with function Next (E : Elmt_Ptr) return Elmt_Ptr;
138 -- The type must provide an internal link for the sake of the
139 -- staticness of the HTable.
141 type Key is limited private;
142 with function Get_Key (E : Elmt_Ptr) return Key;
143 with function Hash (F : Key) return Header_Num;
144 with function Equal (F1, F2 : Key) return Boolean;
146 package Static_HTable is
149 -- Resets the hash table by setting all its elements to Null_Ptr. The
150 -- effect is to clear the hash table so that it can be reused. For the
151 -- most common case where Elmt_Ptr is an access type, and Null_Ptr is
152 -- null, this is only needed if the same table is reused in a new
153 -- context. If Elmt_Ptr is other than an access type, or Null_Ptr is
154 -- other than null, then Reset must be called before the first use
155 -- of the hash table.
157 procedure Set (E : Elmt_Ptr);
158 -- Insert the element pointer in the HTable
160 function Get (K : Key) return Elmt_Ptr;
161 -- Returns the latest inserted element pointer with the given Key
164 procedure Remove (K : Key);
165 -- Removes the latest inserted element pointer associated with the
166 -- given key if any, does nothing if none.
168 function Get_First return Elmt_Ptr;
169 -- Returns Null_Ptr if the Htable is empty, otherwise returns one
170 -- non specified element. There is no guarantee that 2 calls to this
171 -- function will return the same element.
173 function Get_Next return Elmt_Ptr;
174 -- Returns a non-specified element that has not been returned by the
175 -- same function since the last call to Get_First or Null_Ptr if
176 -- there is no such element or Get_First has bever been called. If
177 -- there is no call to 'Set' in between Get_Next calls, all the
178 -- elements of the Htable will be traversed.
186 -- A generic hashing function working on String keys
189 type Header_Num is range <>;
190 function Hash (Key : String) return Header_Num;