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--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                                T A B L E                                 --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1992-2005, Free Software Foundation, Inc.         --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

--  This package provides an implementation of dynamically resizable one

--  dimensional arrays. The idea is to mimic the normal Ada semantics for

--  arrays as closely as possible with the one additional capability of

--  dynamically modifying the value of the Last attribute.

--  Note that this interface should remain synchronized with those in

--  GNAT.Table and GNAT.Dynamic_Tables to keep coherency between these

--  three related units.

with Types; use Types;

package Table is

   pragma Elaborate_Body;

   generic

      type Table_Component_Type is private;

      type Table_Index_Type     is range <>;

      Table_Low_Bound  : Table_Index_Type;

      Table_Initial    : Pos;

      Table_Increment  : Nat;

      Table_Name       : String;

   package Table is

      --  Table_Component_Type and Table_Index_Type specify the type of the

      --  array, Table_Low_Bound is the lower bound. Index_type must be an

      --  integer type. The effect is roughly to declare:

      --    Table : array (Table_Index_Type range Table_Low_Bound .. <>)

      --                       of Table_Component_Type;

      --    Note: since the upper bound can be one less than the lower

      --    bound for an empty array, the table index type must be able

      --    to cover this range, e.g. if the lower bound is 1, then the

      --    Table_Index_Type should be Natural rather than Positive.

      --  Table_Component_Type may be any Ada type, except that controlled

      --  types are not supported. Note however that default initialization

      --  will NOT occur for array components.

      --  The Table_Initial values controls the allocation of the table when

      --  it is first allocated, either by default, or by an explicit Init

      --  call. The value used is Opt.Table_Factor * Table_Initial.

      --  The Table_Increment value controls the amount of increase, if the

      --  table has to be increased in size. The value given is a percentage

      --  value (e.g. 100 = increase table size by 100%, i.e. double it).

      --  The Table_Name parameter is simply use in debug output messages it

      --  has no other usage, and is not referenced in non-debugging mode.

      --  The Last and Set_Last subprograms provide control over the current

      --  logical allocation. They are quite efficient, so they can be used

      --  freely (expensive reallocation occurs only at major granularity

      --  chunks controlled by the allocation parameters).

      --  Note: We do not make the table components aliased, since this would

      --  restict the use of table for discriminated types. If it is necessary

      --  to take the access of a table element, use Unrestricted_Access.

      --  WARNING: On HPPA, the virtual addressing approach used in this unit

      --  is incompatible with the indexing instructions on the HPPA. So when

      --  using this unit, compile your application with -mdisable-indexing.

      --  WARNING: If the table is reallocated, then the address of all its

      --  components will change. So do not capture the address of an element

      --  and then use the address later after the table may be reallocated.

      --  One tricky case of this is passing an element of the table to a

      --  subprogram by reference where the table gets reallocated during

      --  the execution of the subprogram. The best rule to follow is never

      --  to pass a table element as a parameter except for the case of IN

      --  mode parameters with scalar values.

      type Table_Type is

        array (Table_Index_Type range <>) of Table_Component_Type;

      subtype Big_Table_Type is

        Table_Type (Table_Low_Bound .. Table_Index_Type'Last);

      --  We work with pointers to a bogus array type that is constrained

      --  with the maximum possible range bound. This means that the pointer

      --  is a thin pointer, which is more efficient. Since subscript checks

      --  in any case must be on the logical, rather than physical bounds,

      --  safety is not compromised by this approach.

      type Table_Ptr is access all Big_Table_Type;

      --  The table is actually represented as a pointer to allow reallocation

      Table : aliased Table_Ptr := null;

      --  The table itself. The lower bound is the value of Low_Bound.

      --  Logically the upper bound is the current value of Last (although

      --  the actual size of the allocated table may be larger than this).

      --  The program may only access and modify Table entries in the range

      --  First .. Last.

      Locked : Boolean := False;

      --  Table expansion is permitted only if this switch is set to False. A

      --  client may set Locked to True, in which case any attempt to expand

      --  the table will cause an assertion failure. Note that while a table

      --  is locked, its address in memory remains fixed and unchanging. This

      --  feature is used to control table expansion during Gigi processing.

      --  Gigi assumes that tables other than the Uint and Ureal tables do

      --  not move during processing, which means that they cannot be expanded.

      --  The Locked flag is used to enforce this restriction.

      procedure Init;

      --  This procedure allocates a new table of size Initial (freeing any

      --  previously allocated larger table). It is not necessary to call

      --  Init when a table is first instantiated (since the instantiation does

      --  the same initialization steps). However, it is harmless to do so, and

      --  Init is convenient in reestablishing a table for new use.

      function Last return Table_Index_Type;

      pragma Inline (Last);

      --  Returns the current value of the last used entry in the table, which

      --  can then be used as a subscript for Table. Note that the only way to

      --  modify Last is to call the Set_Last procedure. Last must always be

      --  used to determine the logically last entry.

      procedure Release;

      --  Storage is allocated in chunks according to the values given in the

      --  Initial and Increment parameters. A call to Release releases all

      --  storage that is allocated, but is not logically part of the current

      --  array value. Current array values are not affected by this call.

      procedure Free;

      --  Free all allocated memory for the table. A call to init is required

      --  before any use of this table after calling Free.

      First : constant Table_Index_Type := Table_Low_Bound;

      --  Export First as synonym for Low_Bound (parallel with use of Last)

      procedure Set_Last (New_Val : Table_Index_Type);

      pragma Inline (Set_Last);

      --  This procedure sets Last to the indicated value. If necessary the

      --  table is reallocated to accommodate the new value (i.e. on return

      --  the allocated table has an upper bound of at least Last). If Set_Last

      --  reduces the size of the table, then logically entries are removed

      --  from the table. If Set_Last increases the size of the table, then

      --  new entries are logically added to the table.

      procedure Increment_Last;

      pragma Inline (Increment_Last);

      --  Adds 1 to Last (same as Set_Last (Last + 1)

      procedure Decrement_Last;

      pragma Inline (Decrement_Last);

      --  Subtracts 1 from Last (same as Set_Last (Last - 1)

      procedure Append (New_Val : Table_Component_Type);

      pragma Inline (Append);

      --  Equivalent to:

      --    x.Increment_Last;

      --    x.Table (x.Last) := New_Val;

      --  i.e. the table size is increased by one, and the given new item

      --  stored in the newly created table element.

      procedure Set_Item

        (Index : Table_Index_Type;

         Item  : Table_Component_Type);

      pragma Inline (Set_Item);

      --  Put Item in the table at position Index. The table is expanded if

      --  current table length is less than Index and in that case Last is set

      --  to Index. Item will replace any value already present in the table

      --  at this position.

      type Saved_Table is private;

      --  Type used for Save/Restore subprograms

      function Save return Saved_Table;

      --  Resets table to empty, but saves old contents of table in returned

      --  value, for possible later restoration by a call to Restore.

      procedure Restore (T : Saved_Table);

      --  Given a Saved_Table value returned by a prior call to Save, restores

      --  the table to the state it was in at the time of the Save call.

      procedure Tree_Write;

      --  Writes out contents of table using Tree_IO

      procedure Tree_Read;

      --  Initializes table by reading contents previously written

      --  with the Tree_Write call (also using Tree_IO)

   private

      Last_Val : Int;

      --  Current value of Last. Note that we declare this in the private part

      --  because we don't want the client to modify Last except through one of

      --  the official interfaces (since a modification to Last may require a

      --  reallocation of the table).

      Max : Int;

      --  Subscript of the maximum entry in the currently allocated table

      type Saved_Table is record

         Last_Val : Int;

         Max      : Int;

         Table    : Table_Ptr;

      end record;

   end Table;

end Table;