The whole ONES... HASZERO shenanigans is somewhat explained here: https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord https://graphics.stanford.edu/

The whole ONES... HASZERO shenanigans is somewhat explained here: https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord https://graphics.stanford.edu/~seander/bithacks.html#ZeroInW... as well as the entry after it. Edit: And most likely in the excellent book "Hacker's Delight" as well.