On 10 January 2017 at 07:40, Robert Haas <robertmh...@gmail.com> wrote: > On Sat, Jan 7, 2017 at 7:45 PM, Jim Nasby <jim.na...@bluetreble.com> wrote: >> Well, now that there's 3 places that need to do almost the same thing, I >> think it'd be best to just centralize this somewhere. I realize that's not >> going to save any significant amount of code, but it would make it crystal >> clear what's going on (assuming the excellent comment above RIGHTMOST_ONE >> was kept). > > Hmm. This sounds a lot like what fls() and my_log2() also do. I've > been quietly advocating for fls() because we only provide an > implementation in src/port if the operating system doesn't have it, > and the operating system may have an implementation that optimizes to > a single machine-language instruction (bsrl on x86, I think, see > 4f658dc851a73fc309a61be2503c29ed78a1592e). But the fact that our > src/port implementation uses a loop instead of the RIGHTMOST_ONE() > trick seems non-optimal.
It does really sound like we need a bitutils.c as mentioned in [1]. It would be good to make use of GCC's __builtin_popcount [2] instead of the number_of_ones[] array in bitmapset.c. It should be a bit faster and less cache polluting. [1] https://www.postgresql.org/message-id/14578.1462595...@sss.pgh.pa.us [2] https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
