Re: Pentium 1.8Ghz / Windows 2000 / Delphi 6 problem

From: Jamie (jamie_5_not_valid_after_5_Please_at_charter.net)
Date: 10/30/04 

Date: Fri, 29 Oct 2004 18:40:43 -0700

Martin Harvey (Demon account) wrote:

> On Thu, 28 Oct 2004 20:56:17 GMT, pgx@pgrahams.com wrote:
>
>
>>What harm does setting the control word for extended calculations do
>>to other programs, other than making FP results slightly more accurate
>>and slightly slower?
>
>
> This is what makes no sense - altering the FPU control word in your
> process has no effect on anything in any other process.
>
> There are only two ways the Novell stuff can change the FPU control
> word.
>
> 1. Reside in your process as a DLL in user mode ... either registered
> to do something, or as a result of having set a systemwide windows
> hook.
> 2. Run some sort of driver in kernel mode.
>
> In either case, changing the FPU control word and not restoring it is
> a fairly major blunder ... (actually, Novell Netware seems to wreak
> havoc on modern machines, but that's another matter).
>
> Any setting of the FPU control word that you do as a user process does
> not affect any other processes.
>
> MH.
there are many cases where DLL's that your app is using may have a flaw
in it.
   all DLL's that have anything to do with your app will get mapped into
your Application space. video drivers is a good one for this along with
other things.
   if there is any change od the FPU control word not being restored in
any DLL's that your app is using, it does cause problems.
  the FPU control word gets restored to what ever it was when the process
was created or what ever it was when i left the process last.
   when i say process i mean when the OS switches to another process space.!
  this means that any System DLL's including your own that may have some
  code in it that is not property resetting the FPU control word back,
will also effect your app. this how ever, does not apply across process
space.
  my W98 Pc had a bad video driver in it once that would cause my app to
generate a floating point error after i did some graphic work.
   i found this problem after doing lots of debugging on the GDI api's
and found the FPU word had got changed on one of the GDI calls.
  i updated my drivers and it solved the problem there.
    i also started to use the code to make sure the PFU control word was
set to what i wanted there after to make sure.

Relevant Pages

  • Re: Divide by 0 - exception thrown?
    ... do not change the FPU control word and forget to change it back (I am ... to confirm the control word is as it should be). ... far, due to lack of information, I can only *assume* that if other platforms ... use FPUs that follow the IEEE standard, which supports NaNs, that the ...
    (microsoft.public.vc.language)
  • Re: Divide by 0 - exception thrown?
    ... response stating that crashes only occurred after the printer was ... think it is more than clear this is the cause of those crashes. ... It also makes COMPLETE sense that the FPU control word is stored within the ...
    (microsoft.public.vc.language)
  • Re: Pentium 1.8Ghz / Windows 2000 / Delphi 6 problem
    ... >Some DLL perhaps sets the FPU control word wrong, like an OpenGL DLL. ... I had never had to deal with the FPU Control word before. ... double precision rather than extended precision calculations. ...
    (comp.lang.pascal.delphi.misc)
  • Re: floating point arithmetic problems
    ... It's distressingly common for video drivers to ... mess up the floating point control word. ...
    (comp.lang.pascal.delphi.misc)