This sounds like an amazing code-golf-esque project. You would also have to store the last move made by a side to determine if en passant is legal, if the king

This sounds like an amazing code-golf-esque project. You would also have to store the last move made by a side to determine if en passant is legal, if the kings can castle, as well as which side is to move. Reserved values could be used for this as well as flags for other things to improve compression.