bitboards

Array of Bitboards. The index in the array is equal to the ordinal value minus one of the corresponding piece (e.g., Black Knight distribution is at index BN.ordinal - 1).

Each Bitboard has 64 bits, where each bit represents a square in the board, following the Square ordinal order (A1 is bit 0, B1 is bit 1, up to H8 which is bit 63). A bit set to 1 indicates the presence of the piece corresponding to the array index, and 0 indicates absence.