------------------------------------------------------------------------------
--                                                                          --
--                         GNAT RUNTIME COMPONENTS                          --
--                                                                          --
--                       I N T E R F A C E S . C P P                        --
--                                                                          --
--                                 S p e c                                  --
--                                                                          --
--                                                                          --
--          Copyright (C) 1992-2000, 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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-- unit, or you link  this unit with other files  to produce an executable, --
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-- 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.      --
--                                                                          --
------------------------------------------------------------------------------

--  Definitions for interfacing to C++ classes

with System;
with System.Storage_Elements;

package Interfaces.CPP is

   package S   renames System;
   package SSE renames System.Storage_Elements;

   --  This package corresponds to Ada.Tags but applied to tagged types
   --  which are 'imported' from C++ and correspond to exactly to a C++
   --  Class.  GNAT doesn't know about the structure od the C++ dispatch
   --  table (Vtable) but always access it through the procedural interface
   --  defined below, thus the implementation of this package (the body) can
   --  be customized to another C++ compiler without any change in the
   --  compiler code itself as long as this procedural interface is
   --  respected. Note that Ada.Tags defines a very similar procedural
   --  interface to the regular Ada Dispatch Table.

   type Vtable_Ptr is private;

   function Expanded_Name (T : Vtable_Ptr) return String;
   function External_Tag  (T : Vtable_Ptr) return String;

private

   procedure CPP_Set_Prim_Op_Address
     (T        : Vtable_Ptr;
      Position : Positive;
      Value    : S.Address);
   --  Given a pointer to a dispatch Table (T) and a position in the
   --  dispatch Table put the address of the virtual function in it
   --  (used for overriding)

   function CPP_Get_Prim_Op_Address
     (T        : Vtable_Ptr;
      Position : Positive)
      return     S.Address;
   --  Given a pointer to a dispatch Table (T) and a position in the DT
   --  this function returns the address of the virtual function stored
   --  in it (used for dispatching calls)

   procedure CPP_Set_Inheritance_Depth
     (T     : Vtable_Ptr;
      Value : Natural);
   --  Given a pointer to a dispatch Table, stores the value representing
   --  the depth in the inheritance tree. Used during elaboration of the
   --  tagged type.

   function CPP_Get_Inheritance_Depth (T : Vtable_Ptr) return Natural;
   --  Given a pointer to a dispatch Table, retreives the value representing
   --  the depth in the inheritance tree. Used for membership.

   procedure CPP_Set_TSD (T : Vtable_Ptr; Value : S.Address);
   --  Given a pointer T to a dispatch Table, stores the address of the
   --  record containing the Type Specific Data generated by GNAT

   function CPP_Get_TSD (T : Vtable_Ptr) return S.Address;
   --  Given a pointer T to a dispatch Table, retreives the address of the
   --  record containing the Type Specific Data generated by GNAT

   CPP_DT_Prologue_Size : constant SSE.Storage_Count :=
                            SSE.Storage_Count
                              (2 * (Standard'Address_Size / S.Storage_Unit));
   --  Size of the first part of the dispatch table

   CPP_DT_Entry_Size : constant SSE.Storage_Count :=
                         SSE.Storage_Count
                           (1 * (Standard'Address_Size / S.Storage_Unit));
   --  Size of each primitive operation entry in the Dispatch Table.

   CPP_TSD_Prologue_Size : constant SSE.Storage_Count :=
                             SSE.Storage_Count
                               (4 * (Standard'Address_Size / S.Storage_Unit));
   --  Size of the first part of the type specific data

   CPP_TSD_Entry_Size : constant SSE.Storage_Count :=
                          SSE.Storage_Count
                            (Standard'Address_Size / S.Storage_Unit);
   --  Size of each ancestor tag entry in the TSD

   procedure CPP_Inherit_DT
    (Old_T       : Vtable_Ptr;
     New_T       : Vtable_Ptr;
     Entry_Count : Natural);
   --  Entry point used to initialize the DT of a type knowing the
   --  tag of the direct ancestor and the number of primitive ops that are
   --  inherited (Entry_Count).

   procedure CPP_Inherit_TSD
     (Old_TSD : S.Address;
      New_Tag : Vtable_Ptr);
   --  Entry point used to initialize the TSD of a type knowing the
   --  TSD of the direct ancestor.

   function CPP_CW_Membership (Obj_Tag, Typ_Tag : Vtable_Ptr) return Boolean;
   --  Given the tag of an object and the tag associated to a type, return
   --  true if Obj is in Typ'Class.

   procedure CPP_Set_External_Tag (T : Vtable_Ptr; Value : S.Address);
   --  Set the address of the string containing the external tag
   --  in the Dispatch table

   function CPP_Get_External_Tag (T : Vtable_Ptr) return S.Address;
   --  Retrieve the address of a null terminated string containing
   --  the external name

   procedure CPP_Set_Expanded_Name (T : Vtable_Ptr; Value : S.Address);
   --  Set the address of the string containing the expanded name
   --  in the Dispatch table

   function CPP_Get_Expanded_Name (T : Vtable_Ptr) return S.Address;
   --  Retrieve the address of a null terminated string containing
   --  the expanded name

   procedure CPP_Set_Remotely_Callable (T : Vtable_Ptr; Value : Boolean);
   --  Since the notions of spec/body distinction and categorized packages
   --  do not exist in C, this procedure will do nothing

   function CPP_Get_Remotely_Callable (T : Vtable_Ptr) return Boolean;
   --  This function will always return True for the reason explained above

   procedure CPP_Set_RC_Offset (T : Vtable_Ptr; Value : SSE.Storage_Offset);
   --  Sets the Offset of the implicit record controller when the object
   --  has controlled components. Set to O otherwise.

   function CPP_Get_RC_Offset (T : Vtable_Ptr) return SSE.Storage_Offset;
   --  Return the Offset of the implicit record controller when the object
   --  has controlled components. O otherwise.

   function Displaced_This
    (Current_This : S.Address;
     Vptr         : Vtable_Ptr;
     Position     : Positive)
     return         S.Address;
   --  Compute the displacement on the "this" pointer in order to be
   --  compatible with MI.
   --  (used for virtual function calls)

   type Vtable;
   type Vtable_Ptr is access all Vtable;

   pragma Inline (CPP_Set_Prim_Op_Address);
   pragma Inline (CPP_Get_Prim_Op_Address);
   pragma Inline (CPP_Set_Inheritance_Depth);
   pragma Inline (CPP_Get_Inheritance_Depth);
   pragma Inline (CPP_Set_TSD);
   pragma Inline (CPP_Get_TSD);
   pragma Inline (CPP_Inherit_DT);
   pragma Inline (CPP_CW_Membership);
   pragma Inline (CPP_Set_External_Tag);
   pragma Inline (CPP_Get_External_Tag);
   pragma Inline (CPP_Set_Expanded_Name);
   pragma Inline (CPP_Get_Expanded_Name);
   pragma Inline (CPP_Set_Remotely_Callable);
   pragma Inline (CPP_Get_Remotely_Callable);
   pragma Inline (Displaced_This);

end Interfaces.CPP;
