And here's a very recent (still active, in fact) thread on how to add a new intrinsic instruction to hotspot :) http://markmail.org/message/xosi5azzc3hknab7
D. On Fri, Nov 7, 2014 at 8:46 AM, Dawid Weiss <[email protected]> wrote: > And there's always hacker's delight if you're sure popcnt is efficient: > > ctz(x) = pop((x & (−x)) − 1) > ffs(x) = pop(x ^ (~(−x))) > > D. > > On Fri, Nov 7, 2014 at 8:41 AM, Dawid Weiss > <[email protected]> wrote: >> Hi Paul, >> >> I think compiler-dev hotspot list would be adequate. Coincidentally, >> John Rose mentioned ffs (find first bit set) ops just recently and >> gave an interesting link to all sorts of implementations: >> >> http://markmail.org/message/siucbahtw2jzblzl >> >> Dawid >> >> On Thu, Nov 6, 2014 at 5:18 PM, Paul Elschot <[email protected]> >> wrote: >>> Dear all, >>> >>> For LUCENE-6040 it would be good to have better processor support for >>> selecting the i-th set bit from a 64-bit integer. >>> >>> Not too long ago Long.bitCount() was intrinsified in JVM's. >>> >>> I hope something similar will happen to a select(long x, int i) >>> method. However, better processor support is needed first. >>> >>> This is somewhat off topic here, but does anyone know how to request >>> better processor support for select operations? >>> >>> >>> Regards, >>> Paul Elschot >>> >>> --------------------------------------------------------------------- >>> To unsubscribe, e-mail: [email protected] >>> For additional commands, e-mail: [email protected] >>> --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
