1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUNTIME COMPONENTS                          --
4--                                                                          --
5--                            G N A T . T A B L E                           --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--            Copyright (C) 1998-2003 Ada Core Technologies, Inc.           --
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 2,  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.  See the GNU General Public License --
17-- for  more details.  You should have  received  a copy of the GNU General --
18-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
19-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
20-- MA 02111-1307, USA.                                                      --
21--                                                                          --
22-- As a special exception,  if other files  instantiate  generics from this --
23-- unit, or you link  this unit with other files  to produce an executable, --
24-- this  unit  does not  by itself cause  the resulting  executable  to  be --
25-- covered  by the  GNU  General  Public  License.  This exception does not --
26-- however invalidate  any other reasons why  the executable file  might be --
27-- covered by the  GNU Public License.                                      --
28--                                                                          --
29-- GNAT was originally developed  by the GNAT team at  New York University. --
30-- Extensive contributions were provided by Ada Core Technologies Inc.      --
31--                                                                          --
32------------------------------------------------------------------------------
33
34--  Resizable one dimensional array support
35
36--  This package provides an implementation of dynamically resizable one
37--  dimensional arrays. The idea is to mimic the normal Ada semantics for
38--  arrays as closely as possible with the one additional capability of
39--  dynamically modifying the value of the Last attribute.
40
41--  This package provides a facility similar to that of GNAT.Dynamic_Tables,
42--  except that this package declares a single instance of the table type,
43--  while an instantiation of GNAT.Dynamic_Tables creates a type that can be
44--  used to define dynamic instances of the table.
45
46--  Note that this interface should remain synchronized with those in
47--  GNAT.Dynamic_Tables and the GNAT compiler source unit Table to keep
48--  as much coherency as possible between these three related units.
49
50generic
51   type Table_Component_Type is private;
52   type Table_Index_Type     is range <>;
53
54   Table_Low_Bound : Table_Index_Type;
55   Table_Initial   : Positive;
56   Table_Increment : Natural;
57
58package GNAT.Table is
59pragma Elaborate_Body (Table);
60
61   --  Table_Component_Type and Table_Index_Type specify the type of the
62   --  array, Table_Low_Bound is the lower bound. Index_type must be an
63   --  integer type. The effect is roughly to declare:
64
65   --    Table : array (Table_Index_Type range Table_Low_Bound .. <>)
66   --                       of Table_Component_Type;
67
68   --    Note: since the upper bound can be one less than the lower
69   --    bound for an empty array, the table index type must be able
70   --    to cover this range, e.g. if the lower bound is 1, then the
71   --    Table_Index_Type should be Natural rather than Positive.
72
73   --  Table_Component_Type may be any Ada type, except that controlled
74   --  types are not supported. Note however that default initialization
75   --  will NOT occur for array components.
76
77   --  The Table_Initial values controls the allocation of the table when
78   --  it is first allocated, either by default, or by an explicit Init call.
79
80   --  The Table_Increment value controls the amount of increase, if the
81   --  table has to be increased in size. The value given is a percentage
82   --  value (e.g. 100 = increase table size by 100%, i.e. double it).
83
84   --  The Last and Set_Last subprograms provide control over the current
85   --  logical allocation. They are quite efficient, so they can be used
86   --  freely (expensive reallocation occurs only at major granularity
87   --  chunks controlled by the allocation parameters).
88
89   --  Note: we do not make the table components aliased, since this would
90   --  restrict the use of table for discriminated types. If it is necessary
91   --  to take the access of a table element, use Unrestricted_Access.
92
93   --  WARNING: On HPPA, the virtual addressing approach used in this unit
94   --  is incompatible with the indexing instructions on the HPPA. So when
95   --  using this unit, compile your application with -mdisable-indexing.
96
97   --  WARNING: If the table is reallocated, then the address of all its
98   --  components will change. So do not capture the address of an element
99   --  and then use the address later after the table may be reallocated.
100   --  One tricky case of this is passing an element of the table to a
101   --  subprogram by reference where the table gets reallocated during
102   --  the execution of the subprogram. The best rule to follow is never
103   --  to pass a table element as a parameter except for the case of IN
104   --  mode parameters with scalar values.
105
106   type Table_Type is
107     array (Table_Index_Type range <>) of Table_Component_Type;
108
109   subtype Big_Table_Type is
110     Table_Type (Table_Low_Bound .. Table_Index_Type'Last);
111   --  We work with pointers to a bogus array type that is constrained
112   --  with the maximum possible range bound. This means that the pointer
113   --  is a thin pointer, which is more efficient. Since subscript checks
114   --  in any case must be on the logical, rather than physical bounds,
115   --  safety is not compromised by this approach.
116
117   type Table_Ptr is access all Big_Table_Type;
118   --  The table is actually represented as a pointer to allow reallocation
119
120   Table : aliased Table_Ptr := null;
121   --  The table itself. The lower bound is the value of Low_Bound.
122   --  Logically the upper bound is the current value of Last (although
123   --  the actual size of the allocated table may be larger than this).
124   --  The program may only access and modify Table entries in the range
125   --  First .. Last.
126
127   Locked : Boolean := False;
128   --  Table expansion is permitted only if this switch is set to False. A
129   --  client may set Locked to True, in which case any attempt to expand
130   --  the table will cause an assertion failure. Note that while a table
131   --  is locked, its address in memory remains fixed and unchanging.
132
133   procedure Init;
134   --  This procedure allocates a new table of size Initial (freeing any
135   --  previously allocated larger table). It is not necessary to call
136   --  Init when a table is first instantiated (since the instantiation does
137   --  the same initialization steps). However, it is harmless to do so, and
138   --  Init is convenient in reestablishing a table for new use.
139
140   function Last return Table_Index_Type;
141   pragma Inline (Last);
142   --  Returns the current value of the last used entry in the table, which
143   --  can then be used as a subscript for Table. Note that the only way to
144   --  modify Last is to call the Set_Last procedure. Last must always be
145   --  used to determine the logically last entry.
146
147   procedure Release;
148   --  Storage is allocated in chunks according to the values given in the
149   --  Initial and Increment parameters. A call to Release releases all
150   --  storage that is allocated, but is not logically part of the current
151   --  array value. Current array values are not affected by this call.
152
153   procedure Free;
154   --  Free all allocated memory for the table. A call to init is required
155   --  before any use of this table after calling Free.
156
157   First : constant Table_Index_Type := Table_Low_Bound;
158   --  Export First as synonym for Low_Bound (parallel with use of Last)
159
160   procedure Set_Last (New_Val : Table_Index_Type);
161   pragma Inline (Set_Last);
162   --  This procedure sets Last to the indicated value. If necessary the
163   --  table is reallocated to accommodate the new value (i.e. on return
164   --  the allocated table has an upper bound of at least Last). If Set_Last
165   --  reduces the size of the table, then logically entries are removed
166   --  from the table. If Set_Last increases the size of the table, then
167   --  new entries are logically added to the table.
168
169   procedure Increment_Last;
170   pragma Inline (Increment_Last);
171   --  Adds 1 to Last (same as Set_Last (Last + 1)
172
173   procedure Decrement_Last;
174   pragma Inline (Decrement_Last);
175   --  Subtracts 1 from Last (same as Set_Last (Last - 1)
176
177   procedure Append (New_Val : Table_Component_Type);
178   pragma Inline (Append);
179   --  Equivalent to:
180   --    x.Increment_Last;
181   --    x.Table (x.Last) := New_Val;
182   --  i.e. the table size is increased by one, and the given new item
183   --  stored in the newly created table element.
184
185   procedure Set_Item
186     (Index : Table_Index_Type;
187      Item  : Table_Component_Type);
188   pragma Inline (Set_Item);
189   --  Put Item in the table at position Index. The table is expanded if the
190   --  current table length is less than Index and in that case Last is set to
191   --  Index. Item will replace any value already present in the table at this
192   --  position.
193
194   function Allocate (Num : Integer := 1) return Table_Index_Type;
195   pragma Inline (Allocate);
196   --  Adds Num to Last, and returns the old value of Last + 1. Note that
197   --  this function has the possible side effect of reallocating the table.
198   --  This means that a reference X.Table (X.Allocate) is incorrect, since
199   --  the call to X.Allocate may modify the results of calling X.Table.
200
201end GNAT.Table;
202