From: Stefan.Hoffmeister@Econos.de (Stefan Hoffmeister (TeamB))
Subject: Re: Floating-point control word
Date: 25 Jul 1999 00:00:00 GMT
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: "Lluis Olle" <llob@jet.es> wrote:

>1) Who is changing the $1332 (or $1372, as there are some reserved bits in
>the middle), to $1272 ?

Please try searching for "Hoffmeister FPU control word" in the complete
messages archive at http://www.deja.com/ I recall at least two or three
postings to .objectpascal that contain a lengthy explanation showing the
effect.

The short answer is: any DLL has the potential to do this. Just consider
this trivial DLL (I do not know whether it would compile, sorry, but you
will get the idea behind it):


*****************

library WreakHavoc;

const
  BadFpuControlWord = $1332;

procedure DoWreakHavoc; assembler;
asm
  fldcw BadFpuControlWord
end;

procedure DllProcedure(Reason: Integer);
begin
  DLL_PROCESS_ATTACH:
    DoWreakHavoc;

  DLL_THREAD_ATTACH:
    DoWreakHavoc;
end;

begin
  DllProc := @DllProcedure;
  DllProcedure(DLL_PROCESS_ATTACH);
end;

*****************


>has to be changed in some "initialization" code of some unit.

Yes, indeed, and most probably it is caused by loading / initializing the
COM subsystem.


>it seems that "sage.dll", a component of Microsoft Plus!,
>can affect the floating point precission of other tasks in the system. How
>can this be possible in a Win32 enviorment, where each task is isolate from
>others ?

Processes (and threads) are indeed running in separate environments as far
as the CPU and the FPU settings are concerned; but loading a DLL will make
that DLL part of your process / thread. Depending on what the DLL does, it
may affect anything in your code, at any time.



--
Stefan Hoffmeister (TeamB)     http://www.econos.de/
Please do apply judgement when sending email.