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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                            G N A T . T A B L E                           --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                     Copyright (C) 1998-2009, AdaCore                     --

--                                                                          --

-- 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.      --

--                                                                          --

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--  Resizable one dimensional array support

--  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.

--  This package provides a facility similar to that of GNAT.Dynamic_Tables,

--  except that this package declares a single instance of the table type,

--  while an instantiation of GNAT.Dynamic_Tables creates a type that can be

--  used to define dynamic instances of the table.

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

--  GNAT.Dynamic_Tables and the GNAT compiler source unit Table to keep

--  as much coherency as possible between these three related units.

generic

   type Table_Component_Type is private;

   type Table_Index_Type     is range <>;

   Table_Low_Bound : Table_Index_Type;

   Table_Initial   : Positive;

   Table_Increment : Natural;

package GNAT.Table is

   pragma Elaborate_Body;

   --  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 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 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

   --  restrict 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. These types should never

   --  be used by the client.

   type Table_Ptr is access all Big_Table_Type;

   for Table_Ptr'Storage_Size use 0;

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

   --  This type should never be used by the client.

   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.

   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 Append_All (New_Vals : Table_Type);

   --  Appends all components of New_Vals

   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 the

   --  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.

   function Allocate (Num : Integer := 1) return Table_Index_Type;

   pragma Inline (Allocate);

   --  Adds Num to Last, and returns the old value of Last + 1. Note that

   --  this function has the possible side effect of reallocating the table.

   --  This means that a reference X.Table (X.Allocate) is incorrect, since

   --  the call to X.Allocate may modify the results of calling X.Table.

end GNAT.Table;