Category : Pascal Source Code
Archive   : EXTEND5.ZIP
Filename : EXTEND.PAS

{$I-,O-,R-}

unit Extend;

{ This unit allows a program to open more than the standard DOS maximum of 20
open files at one time. You must also be sure to set a FILES=XX statement
in your CONFIG.SYS file. This program installs a special interrupt handler
under DOS 2.x, some semi-documented features under DOS 3.x prior to
DOS 3.3 and the DOS extend files call under DOS 3.3 or later. This
unit USES the DOS unit and should be used before any other units other than
the DOS unit. This code was based upon earlier work by Randy Forgaard, Bela
Lubkin and Kim Kokkonen. See EXTEND.DOC for more information.

Scott Bussinger
Professional Practice Systems
110 South 131st Street
Tacoma, WA 98444
(206)531-8944
Compuserve [72247,2671] }

{ ** Revision History **
1 EXTEND.PAS 9-Mar-89,`SCOTT' First version using TLIB -- Based on 3.2
2 EXTEND.PAS 15-Sep-89,`SCOTT'
Added SwapVectorsExtend procedure
Put handle table into DOS memory
Use DOS 3.3 extended handles function when available
3 EXTEND.PAS 2-Oct-89,`SCOTT'
Fixed bug in determining the DOS version
4 EXTEND.PAS 5-Oct-89,`SCOTT'
Yet another bug in the DosVersion detection
5 EXTEND.PAS 19-Nov-90,`SCOTT'
New version of EXTEND that is compatible with Turbo Pascal 6.0
Modified the documentation and version numbers to be less confusing
** Revision History ** }

interface

procedure SwapVectorsExtend;
{ Swap interrupt vectors taken over by Extend unit with system vectors }

implementation

uses Dos,Shrink;

type HandleArray = array[0..254] of byte; { Room for 255 handles }
HandleArrayPtr = ^HandleArray;

var DosMemory: pointer; { Pointer to memory gained from DOS }
ExitSave: pointer; { Previous exit procedure }
OldInt21: pointer; { Save old INT 21 }
OldHandleTable: HandleArrayPtr; { Pointer to original table }
OldNumHandles: byte; { Original number of handles }

{$L EXTEND }
procedure ExtendInit; external; { Initialize interrupt handler }
procedure ExtendHandler; external; { Replacement INT 21 handler }

procedure SwapVectorsExtend;
{ Swap interrupt vectors taken over by Extend unit with system vectors }
var TempVector: pointer;
begin
if lo(DosVersion) = 2 then
begin
GetIntVec($21,TempVector); { Swap the INT 21 vectors }
SetIntVec($21,OldInt21);
OldInt21 := TempVector
end
end;

procedure ExtendHandles;
{ Install the extended handles interrupt. No files (other than
standard handles) should be open when unit starts up. }
var Regs: Registers;
begin
if lo(DosVersion) = 2
then
begin
GetIntVec($21,OldInt21); { Install interrupt handler under DOS 2.x }
ExtendInit; { Initialize the interrupt handler }
SetIntVec($21,@ExtendHandler)
end
else
begin
DosNewShrink(DosMemory,sizeof(HandleArray));
if DosMemory <> nil then { There wasn't enough memory for a handle table, so just quit }
if (lo(DosVersion)>=4) or (hi(DosVersion)>=30) { Does this DOS version support the handles call? }
then
begin
DosDispose(DosMemory); { Free up the DOS memory block so that the next function will succeed }
with Regs do
begin
AH := $67; { Tell DOS to allow us 255 handles }
BX := 255; { KEEP THIS NUMBER ODD TO AVOID BUG IN SOME VERSIONS OF DOS 3.3!! }
MsDos(Regs)
end
end
else
begin
fillchar(DosMemory^,sizeof(HandleArray),$FF); { Initialize new handles as unused }
OldNumHandles := mem[prefixseg:$0032]; { Get old table length }
OldHandleTable := pointer(ptr(prefixseg,$0034)^); { Save address of old table }
mem[prefixseg:$0032] := sizeof(HandleArray); { Set new table length }
pointer(meml[prefixseg:$0034]) := DosMemory; { Point to new handle table }
move(OldHandleTable^,DosMemory^,OldNumHandles) { Copy the current handle table to the new handle table }
end
end
end;

{$F+}
procedure ExitHandler;
{$F-}
{ Uninstall the extended handles interrupt. All files (other
than standard handles) should be closed before unit exits. }
begin
ExitProc := ExitSave; { Chain to next exit routine }
SwapVectorsExtend { Restore original interrupt vectors }
end;

begin
ExitSave := ExitProc; { Remember the previous exit routine }
ExitProc := @ExitHandler; { Install our exit routine }
ExtendHandles { Enable the extra handles }
end.