File : s-htable.ads
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT RUN-TIME COMPONENTS --
4 -- --
5 -- S Y S T E M . H T A B L E --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 1995-2013, AdaCore --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
17 -- --
18 -- --
19 -- --
20 -- --
21 -- --
22 -- You should have received a copy of the GNU General Public License and --
23 -- a copy of the GCC Runtime Library Exception along with this program; --
24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
25 -- <http://www.gnu.org/licenses/>. --
26 -- --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
29 -- --
30 ------------------------------------------------------------------------------
31
32 -- Hash table searching routines
33
34 -- This package contains two separate packages. The Simple_HTable package
35 -- provides a very simple abstraction that associates one element to one
36 -- key value and takes care of all allocations automatically using the heap.
37 -- The Static_HTable package provides a more complex interface that allows
38 -- complete control over allocation.
39
40 pragma Compiler_Unit_Warning;
41
42 package System.HTable is
43 pragma Preelaborate;
44
45 -------------------
46 -- Simple_HTable --
47 -------------------
48
49 -- A simple hash table abstraction, easy to instantiate, easy to use.
50 -- The table associates one element to one key with the procedure Set.
51 -- Get retrieves the Element stored for a given Key. The efficiency of
52 -- retrieval is function of the size of the Table parameterized by
53 -- Header_Num and the hashing function Hash.
54
55 generic
56 type Header_Num is range <>;
57 -- An integer type indicating the number and range of hash headers
58
59 type Element is private;
60 -- The type of element to be stored
61
62 No_Element : Element;
63 -- The object that is returned by Get when no element has been set for
64 -- a given key
65
66 type Key is private;
67 with function Hash (F : Key) return Header_Num;
68 with function Equal (F1, F2 : Key) return Boolean;
69
70 package Simple_HTable is
71
72 procedure Set (K : Key; E : Element);
73 -- Associates an element with a given key. Overrides any previously
74 -- associated element.
75
76 procedure Reset;
77 -- Removes and frees all elements in the table
78
79 function Get (K : Key) return Element;
80 -- Returns the Element associated with a key or No_Element if the
81 -- given key has no associated element.
82
83 procedure Remove (K : Key);
84 -- Removes the latest inserted element pointer associated with the
85 -- given key if any, does nothing if none.
86
87 function Get_First return Element;
88 -- Returns No_Element if the HTable is empty, otherwise returns one
89 -- non specified element. There is no guarantee that two calls to this
90 -- function will return the same element.
91
92 function Get_Next return Element;
93 -- Returns a non-specified element that has not been returned by the
94 -- same function since the last call to Get_First or No_Element if
95 -- there is no such element. If there is no call to Set in between
96 -- Get_Next calls, all the elements of the HTable will be traversed.
97
98 procedure Get_First (K : in out Key; E : out Element);
99 -- This version of the iterator returns a key/element pair. A non-
100 -- specified entry is returned, and there is no guarantee that two
101 -- calls to this procedure will return the same element. If the table
102 -- is empty, E is set to No_Element, and K is unchanged, otherwise
103 -- K and E are set to the first returned entry.
104
105 procedure Get_Next (K : in out Key; E : out Element);
106 -- This version of the iterator returns a key/element pair. It returns
107 -- a non-specified element that has not been returned since the last
108 -- call to Get_First. If there is no remaining element, then E is set
109 -- to No_Element, and the value in K is unchanged, otherwise K and E
110 -- are set to the next entry. If there is no call to Set in between
111 -- Get_Next calls, all the elements of the HTable will be traversed.
112
113 end Simple_HTable;
114
115 -------------------
116 -- Static_HTable --
117 -------------------
118
119 -- A low-level Hash-Table abstraction, not as easy to instantiate as
120 -- Simple_HTable but designed to allow complete control over the
121 -- allocation of necessary data structures. Particularly useful when
122 -- dynamic allocation is not desired. The model is that each Element
123 -- contains its own Key that can be retrieved by Get_Key. Furthermore,
124 -- Element provides a link that can be used by the HTable for linking
125 -- elements with same hash codes:
126
127 -- Element
128
129 -- +-------------------+
130 -- | Key |
131 -- +-------------------+
132 -- : other data :
133 -- +-------------------+
134 -- | Next Elmt |
135 -- +-------------------+
136
137 generic
138 type Header_Num is range <>;
139 -- An integer type indicating the number and range of hash headers
140
141 type Element (<>) is limited private;
142 -- The type of element to be stored. This is historically part of the
143 -- interface, even though it is not used at all in the operations of
144 -- the package.
145
146 pragma Warnings (Off, Element);
147 -- We have to kill warnings here, because Element is and always
148 -- has been unreferenced, but we cannot remove it at this stage,
149 -- since this unit is in wide use, and it certainly seems harmless.
150
151 type Elmt_Ptr is private;
152 -- The type used to reference an element (will usually be an access
153 -- type, but could be some other form of type such as an integer type).
154
155 Null_Ptr : Elmt_Ptr;
156 -- The null value of the Elmt_Ptr type
157
158 with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
159 with function Next (E : Elmt_Ptr) return Elmt_Ptr;
160 -- The type must provide an internal link for the sake of the
161 -- staticness of the HTable.
162
163 type Key is limited private;
164 with function Get_Key (E : Elmt_Ptr) return Key;
165 with function Hash (F : Key) return Header_Num;
166 with function Equal (F1, F2 : Key) return Boolean;
167
168 package Static_HTable is
169
170 procedure Reset;
171 -- Resets the hash table by setting all its elements to Null_Ptr. The
172 -- effect is to clear the hash table so that it can be reused. For the
173 -- most common case where Elmt_Ptr is an access type, and Null_Ptr is
174 -- null, this is only needed if the same table is reused in a new
175 -- context. If Elmt_Ptr is other than an access type, or Null_Ptr is
176 -- other than null, then Reset must be called before the first use
177 -- of the hash table.
178
179 procedure Set (E : Elmt_Ptr);
180 -- Insert the element pointer in the HTable
181
182 function Get (K : Key) return Elmt_Ptr;
183 -- Returns the latest inserted element pointer with the given Key
184 -- or null if none.
185
186 function Present (K : Key) return Boolean;
187 -- True if an element whose Get_Key is K is in the table
188
189 function Set_If_Not_Present (E : Elmt_Ptr) return Boolean;
190 -- If Present (Get_Key (E)), returns False. Otherwise, does Set (E), and
191 -- then returns True. Present (Get_Key (E)) is always True afterward,
192 -- and the result True indicates E is newly Set.
193
194 procedure Remove (K : Key);
195 -- Removes the latest inserted element pointer associated with the
196 -- given key if any, does nothing if none.
197
198 function Get_First return Elmt_Ptr;
199 -- Returns Null_Ptr if the HTable is empty, otherwise returns one
200 -- non specified element. There is no guarantee that two calls to this
201 -- function will return the same element.
202
203 function Get_Next return Elmt_Ptr;
204 -- Returns a non-specified element that has not been returned by the
205 -- same function since the last call to Get_First or Null_Ptr if
206 -- there is no such element or Get_First has never been called. If
207 -- there is no call to 'Set' in between Get_Next calls, all the
208 -- elements of the HTable will be traversed.
209
210 end Static_HTable;
211
212 ----------
213 -- Hash --
214 ----------
215
216 -- A generic hashing function working on String keys
217
218 generic
219 type Header_Num is range <>;
220 function Hash (Key : String) return Header_Num;
221
222 end System.HTable;