But the major point of this project is to allow for random sampling of positions with a decent likelihood of getting a legal one, which allows for accurate estimation of the number of legal positions.
I consider any reduction past the cache-line size (32B) to have diminishing returns as far as processing is concerned. unless of course if you can fit 2 of these in one.
https://github.com/tromp/ChessPositionRanking
But the major point of this project is to allow for random sampling of positions with a decent likelihood of getting a legal one, which allows for accurate estimation of the number of legal positions.