1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                 G N A T . D Y N A M I C _ H T A B L E S                  --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--                     Copyright (C) 1995-2010, 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
40--  This package provides a facility similar to that of GNAT.HTable, except
41--  that this package declares types that can be used to define dynamic
42--  instances of hash tables, while instantiations in GNAT.HTable creates a
43--  single instance of the hash table.
44
45--  Note that this interface should remain synchronized with those in
46--  GNAT.HTable to keep as much coherency as possible between these two
47--  related units.
48
49with Ada.Unchecked_Deallocation;
50package GNAT.Dynamic_HTables is
51
52   -------------------
53   -- Static_HTable --
54   -------------------
55
56   --  A low-level Hash-Table abstraction, not as easy to instantiate as
57   --  Simple_HTable but designed to allow complete control over the
58   --  allocation of necessary data structures. Particularly useful when
59   --  dynamic allocation is not desired. The model is that each Element
60   --  contains its own Key that can be retrieved by Get_Key. Furthermore,
61   --  Element provides a link that can be used by the HTable for linking
62   --  elements with same hash codes:
63
64   --       Element
65
66   --         +-------------------+
67   --         |       Key         |
68   --         +-------------------+
69   --         :    other data     :
70   --         +-------------------+
71   --         |     Next Elmt     |
72   --         +-------------------+
73
74   generic
75      type Header_Num is range <>;
76      --  An integer type indicating the number and range of hash headers
77
78      type Element (<>) is limited private;
79      --  The type of element to be stored
80
81      type Elmt_Ptr is private;
82      --  The type used to reference an element (will usually be an access
83      --  type, but could be some other form of type such as an integer type).
84
85      Null_Ptr : Elmt_Ptr;
86      --  The null value of the Elmt_Ptr type
87
88      with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
89      with function  Next     (E : Elmt_Ptr) return Elmt_Ptr;
90      --  The type must provide an internal link for the sake of the
91      --  staticness of the HTable.
92
93      type Key is limited private;
94      with function Get_Key (E : Elmt_Ptr) return Key;
95      with function Hash    (F : Key)      return Header_Num;
96      with function Equal   (F1, F2 : Key) return Boolean;
97
98   package Static_HTable is
99
100      type Instance is private;
101      Nil : constant Instance;
102
103      procedure Reset (T : in out Instance);
104      --  Resets the hash table by releasing all memory associated with
105      --  it. The hash table can safely be reused after this call. For the
106      --  most common case where Elmt_Ptr is an access type, and Null_Ptr is
107      --  null, this is only needed if the same table is reused in a new
108      --  context. If Elmt_Ptr is other than an access type, or Null_Ptr is
109      --  other than null, then Reset must be called before the first use of
110      --  the hash table.
111
112      procedure Set (T : in out Instance; E : Elmt_Ptr);
113      --  Insert the element pointer in the HTable
114
115      function Get (T : Instance; K : Key) return Elmt_Ptr;
116      --  Returns the latest inserted element pointer with the given Key
117      --  or null if none.
118
119      procedure Remove (T : Instance; K : Key);
120      --  Removes the latest inserted element pointer associated with the
121      --  given key if any, does nothing if none.
122
123      function Get_First (T : Instance) return Elmt_Ptr;
124      --  Returns Null_Ptr if the Htable is empty, otherwise returns one
125      --  non specified element. There is no guarantee that 2 calls to this
126      --  function will return the same element.
127
128      function Get_Next (T : Instance) return Elmt_Ptr;
129      --  Returns a non-specified element that has not been returned by the
130      --  same function since the last call to Get_First or Null_Ptr if
131      --  there is no such element or Get_First has never been called. If
132      --  there is no call to 'Set' in between Get_Next calls, all the
133      --  elements of the Htable will be traversed.
134
135   private
136
137      type Instance_Data;
138      type Instance is access all Instance_Data;
139      Nil : constant Instance := null;
140
141   end Static_HTable;
142
143   -------------------
144   -- Simple_HTable --
145   -------------------
146
147   --  A simple hash table abstraction, easy to instantiate, easy to use.
148   --  The table associates one element to one key with the procedure Set.
149   --  Get retrieves the Element stored for a given Key. The efficiency of
150   --  retrieval is function of the size of the Table parameterized by
151   --  Header_Num and the hashing function Hash.
152
153   generic
154      type Header_Num is range <>;
155      --  An integer type indicating the number and range of hash headers
156
157      type Element is private;
158      --  The type of element to be stored
159
160      No_Element : Element;
161      --  The object that is returned by Get when no element has been set for
162      --  a given key
163
164      type Key is private;
165      with function Hash  (F : Key)      return Header_Num;
166      with function Equal (F1, F2 : Key) return Boolean;
167
168   package Simple_HTable is
169
170      type Instance is private;
171      Nil : constant Instance;
172
173      procedure Set (T : in out Instance; K : Key; E : Element);
174      --  Associates an element with a given key. Overrides any previously
175      --  associated element.
176
177      procedure Reset (T : in out Instance);
178      --  Releases all memory associated with the table. The table can be
179      --  reused after this call (it is automatically allocated on the first
180      --  access to the table).
181
182      function Get (T : Instance; K : Key) return Element;
183      --  Returns the Element associated with a key or No_Element if the
184      --  given key has not associated element
185
186      procedure Remove (T : Instance; K : Key);
187      --  Removes the latest inserted element pointer associated with the
188      --  given key if any, does nothing if none.
189
190      function Get_First (T : Instance) return Element;
191      --  Returns No_Element if the Htable is empty, otherwise returns one
192      --  non specified element. There is no guarantee that two calls to this
193      --  function will return the same element, if the Htable has been
194      --  modified between the two calls.
195
196      function Get_Next (T : Instance) return Element;
197      --  Returns a non-specified element that has not been returned by the
198      --  same function since the last call to Get_First or No_Element if
199      --  there is no such element. If there is no call to 'Set' in between
200      --  Get_Next calls, all the elements of the Htable will be traversed.
201      --  To guarantee that all the elements of the Htable will be traversed,
202      --  no modification of the Htable (Set, Reset, Remove) should occur
203      --  between a call to Get_First and subsequent consecutive calls to
204      --  Get_Next, until one of these calls returns No_Element.
205
206   private
207
208      type Element_Wrapper;
209      type Elmt_Ptr is access all Element_Wrapper;
210      type Element_Wrapper is record
211         K    : Key;
212         E    : Element;
213         Next : Elmt_Ptr;
214      end record;
215
216      procedure Free is new
217        Ada.Unchecked_Deallocation (Element_Wrapper, Elmt_Ptr);
218
219      procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
220      function  Next     (E : Elmt_Ptr) return Elmt_Ptr;
221      function  Get_Key  (E : Elmt_Ptr) return Key;
222
223      package Tab is new Static_HTable
224        (Header_Num => Header_Num,
225         Element    => Element_Wrapper,
226         Elmt_Ptr   => Elmt_Ptr,
227         Null_Ptr   => null,
228         Set_Next   => Set_Next,
229         Next       => Next,
230         Key        => Key,
231         Get_Key    => Get_Key,
232         Hash       => Hash,
233         Equal      => Equal);
234
235      type Instance is new Tab.Instance;
236      Nil : constant Instance := Instance (Tab.Nil);
237
238   end Simple_HTable;
239
240end GNAT.Dynamic_HTables;
241