[acomar]

most of the optimizations discussed are actually kind of obvious if you know how chess notation works in the first place. like the reason the starting move "Nf3" makes any sense is because only 1 knight of all 4 on the board can possibly move to f3 on the first move. what the OP is doing is trying to take that kind of information density and trying to represent it, first by assigning bits to each part of a possible move and then by paring it down where the space of legal moves excludes entire categories of possibilities. there's another article that goes much further into how much optimization is possible here: https://lichess.org/@/lichess/blog/developer-update-275-impr...