Ron <rjpeace@earthlink.net> writes:
> For an even more extreme speedup, don't most modern CPUs have an asm
> instruction that counts the bits (un)set (AKA "population counting")
> in various size entities (4b, 8b, 16b, 32b, 64b, and 128b for 64b
> CPUs with SWAR instructions)?
Yeah, but fetching from a small constant table is pretty quick too;
I doubt it's worth getting involved in machine-specific assembly code
for this. I'm much more interested in the idea of improving the
furthest-distance algorithm in gtsvector_picksplit --- if we can do
that, it'll probably drop the distance calculation down to the point
where it's not really worth the trouble to assembly-code it.
regards, tom lane
