Table of legal moves for occupancies
int64 numbers for bishops and rooks
B2G7 mask to shorten table
...keys give same results, but must
...occ&=0x007E7E7E7E7E7E00 for squares inner B2G7
occupancy - the b2-g7 blockers only
...as a key to lookup
Unique results to see cases statistics
...min(occ1,occ2,...,occ3) as unusable key
...to list possible legal move cases only