------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
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--                                T A B L E                                 --
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--                            $Revision: 1.28 $                             --
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--   Copyright (C) 1992,1993,1994,1995,1996 Free Software Foundation, Inc.  --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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------------------------------------------------------------------------------

with Types; use Types;

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

--  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.

   --  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_Low_Bound .. <>) of Table_Component_Type;

   --  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.

   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.

   First : constant Table_Index_Type := Table_Low_Bound;
   --  Export First as synonym for Low_Bound (to be 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 accomodate 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).

   function Allocate (Num : Int := 1) return Table_Index_Type;
   pragma Inline (Allocate);
   --  Adds Num to Last, and returns the old value of Last + 1.

   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;
