1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- T A B L E -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2019, Free Software Foundation, 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 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-- This package provides an implementation of dynamically resizable one 33-- dimensional arrays. The idea is to mimic the normal Ada semantics for 34-- arrays as closely as possible with the one additional capability of 35-- dynamically modifying the value of the Last attribute. 36 37-- This package uses a very efficient memory management scheme and any 38-- change must be carefully evaluated on compilation of real software. 39 40-- Note that this interface should remain synchronized with those in 41-- GNAT.Table and GNAT.Dynamic_Tables to keep coherency between these 42-- three related units. 43 44with Types; use Types; 45 46package Table is 47 pragma Elaborate_Body; 48 49 generic 50 type Table_Component_Type is private; 51 type Table_Index_Type is range <>; 52 53 Table_Low_Bound : Table_Index_Type; 54 Table_Initial : Pos; 55 Table_Increment : Nat; 56 Table_Name : String; 57 Release_Threshold : Nat := 0; 58 59 package Table is 60 61 -- Table_Component_Type and Table_Index_Type specify the type of the 62 -- array, Table_Low_Bound is the lower bound. Table_Index_Type must be 63 -- an 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 79 -- call. The value used is Opt.Table_Factor * Table_Initial. 80 81 -- The Table_Increment value controls the amount of increase, if the 82 -- table has to be increased in size. The value given is a percentage 83 -- value (e.g. 100 = increase table size by 100%, i.e. double it). 84 85 -- The Table_Name parameter is simply use in debug output messages it 86 -- has no other usage, and is not referenced in non-debugging mode. 87 88 -- The Last and Set_Last subprograms provide control over the current 89 -- logical allocation. They are quite efficient, so they can be used 90 -- freely (expensive reallocation occurs only at major granularity 91 -- chunks controlled by the allocation parameters). 92 93 -- Note: We do not make the table components aliased, since this would 94 -- restrict the use of table for discriminated types. If it is necessary 95 -- to take the access of a table element, use Unrestricted_Access. 96 97 -- WARNING: On HPPA, the virtual addressing approach used in this unit 98 -- is incompatible with the indexing instructions on the HPPA. So when 99 -- using this unit, compile your application with -mdisable-indexing. 100 101 -- WARNING: If the table is reallocated, then the address of all its 102 -- components will change. So do not capture the address of an element 103 -- and then use the address later after the table may be reallocated. 104 -- One tricky case of this is passing an element of the table to a 105 -- subprogram by reference where the table gets reallocated during 106 -- the execution of the subprogram. The best rule to follow is never 107 -- to pass a table element as a parameter except for the case of IN 108 -- mode parameters with scalar values. 109 110 type Table_Type is 111 array (Table_Index_Type range <>) of Table_Component_Type; 112 113 subtype Big_Table_Type is 114 Table_Type (Table_Low_Bound .. Table_Index_Type'Last); 115 -- We work with pointers to a bogus array type that is constrained 116 -- with the maximum possible range bound. This means that the pointer 117 -- is a thin pointer, which is more efficient. Since subscript checks 118 -- in any case must be on the logical, rather than physical bounds, 119 -- safety is not compromised by this approach. 120 121 type Table_Ptr is access all Big_Table_Type; 122 for Table_Ptr'Storage_Size use 0; 123 -- The table is actually represented as a pointer to allow reallocation 124 125 Table : aliased Table_Ptr := null; 126 -- The table itself. The lower bound is the value of Low_Bound. 127 -- Logically the upper bound is the current value of Last (although 128 -- the actual size of the allocated table may be larger than this). 129 -- The program may only access and modify Table entries in the range 130 -- First .. Last. 131 132 Locked : Boolean := False; 133 -- Table expansion is permitted only if this switch is set to False. A 134 -- client may set Locked to True, in which case any attempt to expand 135 -- the table will cause an assertion failure. Note that while a table 136 -- is locked, its address in memory remains fixed and unchanging. This 137 -- feature is used to control table expansion during Gigi processing. 138 -- Gigi assumes that tables other than the Uint and Ureal tables do 139 -- not move during processing, which means that they cannot be expanded. 140 -- The Locked flag is used to enforce this restriction. 141 142 procedure Init; 143 -- This procedure allocates a new table of size Initial (freeing any 144 -- previously allocated larger table). It is not necessary to call 145 -- Init when a table is first instantiated (since the instantiation does 146 -- the same initialization steps). However, it is harmless to do so, and 147 -- Init is convenient in reestablishing a table for new use. 148 149 function Last return Table_Index_Type; 150 pragma Inline (Last); 151 -- Returns the current value of the last used entry in the table, which 152 -- can then be used as a subscript for Table. Note that the only way to 153 -- modify Last is to call the Set_Last procedure. Last must always be 154 -- used to determine the logically last entry. 155 156 procedure Release; 157 -- Storage is allocated in chunks according to the values given in the 158 -- Initial and Increment parameters. If Release_Threshold is 0 or the 159 -- length of the table does not exceed this threshold then a call to 160 -- Release releases all storage that is allocated, but is not logically 161 -- part of the current array value; otherwise the call to Release leaves 162 -- the current array value plus 0.1% of the current table length free 163 -- elements located at the end of the table (this parameter facilitates 164 -- reopening large tables and adding a few elements without allocating a 165 -- chunk of memory). In both cases current array values are not affected 166 -- by this call. 167 168 procedure Free; 169 -- Free all allocated memory for the table. A call to init is required 170 -- before any use of this table after calling Free. 171 172 First : constant Table_Index_Type := Table_Low_Bound; 173 -- Export First as synonym for Low_Bound (parallel with use of Last) 174 175 procedure Set_Last (New_Val : Table_Index_Type); 176 pragma Inline (Set_Last); 177 -- This procedure sets Last to the indicated value. If necessary the 178 -- table is reallocated to accommodate the new value (i.e. on return 179 -- the allocated table has an upper bound of at least Last). If Set_Last 180 -- reduces the size of the table, then logically entries are removed 181 -- from the table. If Set_Last increases the size of the table, then 182 -- new entries are logically added to the table. 183 184 procedure Increment_Last; 185 pragma Inline (Increment_Last); 186 -- Adds 1 to Last (same as Set_Last (Last + 1) 187 188 procedure Decrement_Last; 189 pragma Inline (Decrement_Last); 190 -- Subtracts 1 from Last (same as Set_Last (Last - 1) 191 192 procedure Append (New_Val : Table_Component_Type); 193 pragma Inline (Append); 194 -- Equivalent to: 195 -- x.Increment_Last; 196 -- x.Table (x.Last) := New_Val; 197 -- i.e. the table size is increased by one, and the given new item 198 -- stored in the newly created table element. 199 200 procedure Append_All (New_Vals : Table_Type); 201 -- Appends all components of New_Vals 202 203 procedure Set_Item 204 (Index : Table_Index_Type; 205 Item : Table_Component_Type); 206 pragma Inline (Set_Item); 207 -- Put Item in the table at position Index. The table is expanded if 208 -- current table length is less than Index and in that case Last is set 209 -- to Index. Item will replace any value already present in the table 210 -- at this position. 211 212 type Saved_Table is private; 213 -- Type used for Save/Restore subprograms 214 215 function Save return Saved_Table; 216 -- Resets table to empty, but saves old contents of table in returned 217 -- value, for possible later restoration by a call to Restore. 218 219 procedure Restore (T : Saved_Table); 220 -- Given a Saved_Table value returned by a prior call to Save, restores 221 -- the table to the state it was in at the time of the Save call. 222 223 procedure Tree_Write; 224 -- Writes out contents of table using Tree_IO 225 226 procedure Tree_Read; 227 -- Initializes table by reading contents previously written with the 228 -- Tree_Write call (also using Tree_IO). 229 230 private 231 232 Last_Val : Int; 233 -- Current value of Last. Note that we declare this in the private part 234 -- because we don't want the client to modify Last except through one of 235 -- the official interfaces (since a modification to Last may require a 236 -- reallocation of the table). 237 238 Max : Int; 239 -- Subscript of the maximum entry in the currently allocated table 240 241 type Saved_Table is record 242 Last_Val : Int; 243 Max : Int; 244 Table : Table_Ptr; 245 end record; 246 247 end Table; 248end Table; 249