On Fri, 2013-06-07 at 11:48 +0100, David Laight wrote: > > For those interested, this is the Quake3 sqrt from Carmack ... > there's > > plenty of literature about it one or two google clicks away :-) > > I guess that is a rough enough approximation for graphics. > > However it will be miscompiled unless i and y are put in a union.
It won't in the kernel disables strict aliasing :-) Anyway, that was just a hack and plenty enough to get anaconda going, the bloody thing only uses fsqrt because it's python crappola does something like exp(1.0) / sqrt(2.0) as part of its random number stuff. Honestly I could have made it just return 1.0 and it would probably have worked :-) However, my point remains, it would be very much worthwhile for the kernel to have some reasonable emulation of those missing instructions (afaik only a handful) like we have for isel, popcnt* etc... especially since distros seem to be keen on enabling the use of them in their toolchain. I don't personally have the bandwidth to do a clean implementation (that handles FP exceptions, NaNs, FPSCR, etc...) but I believe it would be valuable if somebody else did (hint hint hint :-) since without this, Fedora ppc64 is basically going to be a non-started on those chips. BTW. Did you guys (ie. FSL) finally add fsqrt to e6500 or it's still out ? Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
