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6.15.10 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) 1998-2005 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);
     procedure OvrInitEMS;
     procedure OvrSetBuf (Size: LongInt);
     function  OvrGetBuf: LongInt;
     procedure OvrSetRetry (Size: LongInt);
     function  OvrGetRetry: LongInt;
     procedure OvrClearBuf;