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#### BP compatibility: Overlay

The following listing contains the interface of the Overlay unit.

This is just a dummy replacement for BP's `Overlay` unit, since GPC doesn't need overlays.

         { Dummy BP compatible overlay unit for GPC

           Copyright (C) 1998-2004 Free Software Foundation, Inc.

           Author: Frank Heckenbach <frank@pascal.gnu.de>

           This file is part of GNU Pascal.

           GNU Pascal is free software; you can redistribute it and/or modify
           it under the terms of the GNU General Public License as published
           by the Free Software Foundation; either version 2, or (at your
           option) any later version.

           GNU Pascal is distributed in the hope that it will be useful, but
           WITHOUT 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
           along with GNU Pascal; see the file COPYING. If not, write to the
           Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA
           02111-1307, USA.

           As a special exception, if you link this file with files compiled
           with a GNU compiler to produce an executable, this does not 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
           General Public License. }

         {$gnu-pascal,I-}
         {$if __GPC_RELEASE__ < 20030412}
         {$error This unit requires GPC release 20030412 or newer.}
         {$endif}

         unit Overlay;

         interface

         const
           OvrOK = 0;
           OvrError = -1;
           OvrNotFound = -2;
           OvrNoMemory = -3;
           OvrIOError = -4;
           OvrNoEMSDriver = -5;
           OvrNoEMSMemory = -6;

         const
           OvrEmsPages: Word = 0;
           OvrTrapCount: Word = 0;
           OvrLoadCount: Word = 0;
           OvrFileMode: Byte = 0;

         type
           OvrReadFunc = function (OvrSeg: Word): Integer;

         var
           OvrReadBuf: OvrReadFunc;
           OvrResult: Integer = 0;

         procedure OvrInit (aFileName: String); attribute (name
           = '_p_OvrInit');
         procedure OvrInitEMS; attribute (name = '_p_OvrInitEMS');
         procedure OvrSetBuf (Size: LongInt); attribute (name
           = '_p_OvrSetBuf');
         function  OvrGetBuf: LongInt; attribute (name = '_p_OvrGetBuf');
         procedure OvrSetRetry (Size: LongInt); attribute (name
           = '_p_OvrSetRetry');
         function  OvrGetRetry: LongInt; attribute (name = '_p_OvrGetRetry');
         procedure OvrClearBuf; attribute (name = '_p_OvrClearBuf');