On Jun 7, 2013, at 7:14 AM, Benjamin Herrenschmidt wrote: > 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.
Pretty sure fsqrt is still out of e6500. - k _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev