Re: Arithmetic rounding

From: JRG <"JRG">
Date: Wed, 19 Jun 2002 13:01:13 -0400

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On 19 Jun 02, at 17:19, robert.d.campbell{([at]})nowhere.xy

>
> I think that the two routines below read and set
> the i386 floating point control register.
>
>
> PROCEDURE [code] Read (VAR n : SHORTINT)
> 0D9H, 038H; (* FSTCW -> n *)
>
>
> PROCEDURE [code] Write (VAR flgs : SET)
> 0D9H, 028H; (* flgs -> FLDCW *)
>
>
> However it seems to be reset to a default value
> at (so far) unpredicable times. I suspect that use
> of a Formatter causes this.
>
>
> Robert Campbell
>


I once wrote similar stuff, long long ago, in a different language.
If I
recall
correctly, you have to be VERY careful because lots of programs
are very
unfriendly about how they use the FPU. So, your apparently
correct
routine
may fail simply because some other process running in the
Windows
environment decides to tinker with the control registers of the
FPU, and
then
neglects to put them back the way they were when it exits.

---JRG


John R. Gleason

Syracuse University
430 Huntington Hall Voice: 315-443-3107
Syracuse, NY 13244-2340 USA FAX: 315-443-4085

PGP public key at keyservers
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Received on Wed Jun 19 2002 - 19:01:13 UTC