Michael Justin’s Weblog

A strange problem suddenly occurs in all my Delphi 7 and Delphi 2009 unit tests.

I used DUnit CheckEquals to compare two Currency values, like

CheckEquals(1.99, SomeCurrencyValue);

This worked fine in the IDE and in our build scripts, which run using the same version of DUnit for two years. Now, all of a sudden, all tests fail with strange error messages like

Expected: <1.99> - Found: <1.99>

With some newsgroup help I found that something has changed a processor flag which is responsible for floating point operations. Digging deeper in my unit tests, I found the root cause in the IBX component TIBDatabase, which seems to modify this flag.

TIBDataBase.Create(nil) changes the value of Get8087CW from $1372 to $1272, a very strange value.

procedure TForm2.Button1Click(Sender: TObject);
begin
Memo1.Lines.Add(Format('FPU CW = $%4.4X',[Get8087CW]));
TIBDataBase.Create(nil);
Memo1.Lines.Add(Format('FPU CW = $%4.4X',[Get8087CW]));
end;

Tested on two systems running Windows 2000 SP 4, InterBase 7.5.1 and 2007 libraries (gds32.dll), Delphi 7 and Delphi 2009

This code in a GUI application compiles and runs (tested with Delphi 6 and 2009):

procedure TForm1.Button1Click(Sender: TObject);
begin
Self := TForm1.Create(Owner);
end;

Questions that come to mind:

• why is Self writeable and not read-only?
• in which situations could this be useful?

If you know the answer, I would be happy if you post it here or at stackoverflow.