PPC float context only 4 Bytes per register?

Sergei Organov osv at javad.ru
Mon Nov 12 11:15:32 UTC 2001


Dear Thomas,

I've also noticed this some time ago and even posted my observations to this
list. However, it seems that nobody had time willingness to fix this, so I
still use old exception processing code that doesn't have this problem.

BR,
Sergei Organov.


"Thomas Doerfler" <Thomas.Doerfler at imd-systems.de> writes:
> Hi,
> 
> I have just had some looks into the 
> libcpu/powerpc/new_exception_processing/cpu_asm.S code to 
> save/restore a floating-point context. In there it seems that 
> for every context switch all the float registers are saved 
> into 4 byte locations (in "single" precision format). 
> 
> >From my point of view this results in rounding errors for 
> "double precision" (64 bit) float arithmetics. So if I have 
> written some code using "double precision" variables I will 
> get roundoff errors, if there has been a context switch during 
> calculations. (I did not try that out, but it seems logical to 
> me...)
> 
> Did I miss something there?
> 
> Any comments welcome...
> 
> 	Thomas Doerfler.
> --------------------------------------------
> IMD Ingenieurbuero fuer Microcomputertechnik
> Thomas Doerfler           Herbststrasse 8
> D-82178 Puchheim          Germany
> email:    Thomas.Doerfler at imd-systems.de
> PGP public key available at: http://www.imd-
> systems.de/pgp_key.htm




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