Popcount table generated at compile-time using ct_expand. See https://gist.github.com/901235

popcount.erl

-module(popcount).
-compile({parse_transform, ct_expand}).
-compile({popcount_table}).
-export([popcount16/1, popcount32/1]).

-define(TABLE(B), ct_expand:term( popcount_table:gen_table(B) )).
-define(TABLE16, ct_expand:term( ?TABLE(16) )).

popcount16(V) -> erlang:element(V+1, ?TABLE16).
popcount32(V) -> popcount16( V band 16#ffff )
    + popcount16( (V bsr 16) band 16#ffff).