# [MATL], 5 bytes

    3Z%Bz

[Try it online!][TIO-j5o5jm21]

[MATL]: https://github.com/lmendo/MATL
[TIO-j5o5jm21]: https://tio.run/##y00syfn/3zhK1anq/38jIwA "MATL – Try It Online"

Exact transliteration of my MATLAB answer. Note that input and output are implicit. -2 bytes thanks to Luis Mendo.

    3Z%   % Typecast: changes input (implicitly taken and converted to double) to uint64 without changing underlying bits
    B     % Convert integer to array of 1s and 0s
    z     % Count nonzero entries