From: "Tony Ingenoso" 

You can't - its entirely under app control and MUST be set on a per thread
basis, and sometimes altered often during the execution of any given
thread.  Every thread in the system will have its own NPX context that must
be saved/restored on context swaps.

The loader could init an app with some chosen setting, but most
apps/threads will do an FINIT instruction then setup the kinds of rounding
and exception masking they intend to use.

The only way (very grusome) to subvert an apps behavior in the OS would be
to init the app with the NPX emulation bit set, then have the OS field an
exception on EVERY numeric opcode encountered, examine that instruction to
see if it altered the NPX control word rounding bits, and ignore it if it
did.  Apps that needed say round up to give correct answers that were
forced into say chop this way would all produce bogus results.  NPX
performance with a scheme like this would be horrendous.


"Geo."  wrote in message
news:3dcd368b$1{at}w3.nls.net...
> Riiiight, and as an end user how does one set this system wide?
>
> Geo.
>
> "Tony Ingenoso"  wrote in message
> news:3dcc8297{at}w3.nls.net...
> > There's four available founding modes in 754 standard.  up, down, nearest,
> and chop to zero.
> >
> > Its entirely up to the applications to set the most appropriate rounding
> mode for the task at hand.  In extreme cases, you may be
> > changing it constantly between NPX calc operations.  If you don't
> explicitly set this to what you want, you may get answers other
> > than what you want ;->

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