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) 1995-2018, 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-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
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
40pragma Compiler_Unit_Warning;
41
42package 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
222end System.HTable;
223