Move Generation with Perfect Hash Functions

We present two new perfect hashing schemes that can be used for efficient bitboard move generation for sliding pieces in chess-like board games without the need to use rotated bitboards. Moreover, we show that simple variations of these schemes give minimal perfect hashing schemes. The new method is applicable provided N , the number of k-bit spaced positions that may be set to 1, is not more than k + 1. In chess, for a Rook’s movement along a file N = k = 8; for a Bishop’s movement N ≤ 8, and k = 9 for a north-east diagonal and k = 7 for a north-west diagonal. The results of computational experiments comparing the efficiency of move generation with the standard method show that using the hashing scheme gives an average improvement of approximately 40%. The schemes we suggest are simple, efficient, and easy to understand and implement.