You can also go faster using SIMD instructions if you need to compute wider population counts (beyond 64 bits): Faster Population Counts Using AVX2 Instruction

You can also go faster using SIMD instructions if you need to compute wider population counts (beyond 64 bits): Faster Population Counts Using AVX2 Instructions, Computer Journal, Volume 61, Issue 1, 2018 https://arxiv.org/abs/1611.07612 https://arxiv.org/abs/1611.07612