Re: netwinder floating point

[Peter Teichmann <lists@peter-teichmann.de>]

Am Donnerstag, 6. Januar 2005 21:48 schrieb Jim Buttafuoco:
Hi Jim,

> I get 2 different answers for sqrt(200).  with the fastfpe giving a
> different answer from lets say i386 while the nwfte give the exact answer
> that i386 does.

I can reproduce this on my bast, so no need to reboot your netwinder. The 
problem ist, that I did not implement correct rounding for the sqrt 
algorithm, because this involves a bit thinking to do it correctly. So, if 
you use FastFPE, the LSB of the result of an sqrt instruction can be wrong 
with a chance of 50%. For most applications this is tolerable. Nevertheless, 
I will correct this once I have time. Would you offer yourself as test person 
for the fix once it is done?

If it is a program compiled by yourself, you can avoid the problem by using 
the -O0 optimisation switch, this lets gcc not inline the sqrt instruction, 
but instead call a library function which does the work by hand.

Peter Teichmann