Hello eyepopslikeamosquito,

The CPAN module Bit::Fast has a function popcountl, implemented in C, which operates on 64-bit integers and is claimed to be fast.

Disclaimer: I haven’t been able to test it because — although I have a 64-bit OS and a 64-bit Perl with USE_64_BIT_INT defined — my Perl was apparently built with LONGSIZE defined as 4, not 8, so (with use Config) $Config{longsize} == 4 and popcountl doesn’t get built. I confess I don’t understand the issues involved here — maybe just a configuration problem?

Anyway, hope that’s of interest,