def is_legal_king_move(self, move):
"""
Pseudo-Legal King Moves: one step in any direction
:param move: the proposed Move instance
:return: True iff Move is legal
"""
bitboard = make_uint64()
moving_to_square = set_bit(bitboard, move.to_sq)
for i in [8, -8]:
# North-South
bitboard |= set_bit(bitboard, np.uint64(move.from_sq + i))
for i in [1, 9, -7]:
# East (mask the A file)
bitboard |= set_bit(bitboard, np.uint64(move.from_sq + i) & ~np.uint64(File.hexA))
for i in [-1, -9, 7]:
# West (mask the H file)
bitboard |= set_bit(bitboard, np.uint64(move.from_sq + i) & ~np.uint64(File.hexH))
occupied_squares = {
Color.BLACK: self.board.black_pieces_bb,
Color.WHITE: self.board.white_pieces_bb,
}
# remove own piece targets
own_piece_targets = occupied_squares[self.color_to_move] & moving_to_square
if own_piece_targets:
bitboard &= ~own_piece_targets
return bitboard
def is_legal_rook_move(self, move: Move) -> bool:
"""
Pseudo-Legal Rook Moves
Implements the classical approach for determining legal sliding-piece moves
for rank and file directions. Gets first blocker with forward or reverse bitscan
based on the ray direction and XORs the open board ray with the ray continuation
from the blocked square.
:param move: the proposed Move instance
:return: True iff Move is legal
"""
bitboard = make_uint64()
moving_to_square = set_bit(bitboard, move.to_sq)
occupied = self.board.occupied_squares_bb
# north route
north_ray = get_north_ray(bitboard, move.from_sq)
intersection = occupied & north_ray
if intersection:
first_blocker = bitscan_forward(intersection)
block_ray = get_northwest_ray(bitboard, first_blocker)
north_ray ^= block_ray
# east route
east_ray = get_east_ray(bitboard, move.from_sq)
intersection = occupied & east_ray
if intersection:
first_blocker = bitscan_forward(intersection)
block_ray = get_northeast_ray(bitboard, first_blocker)
east_ray ^= block_ray
# south route
south_ray = get_south_ray(bitboard, move.from_sq)
intersection = occupied & south_ray
if intersection:
first_blocker = bitscan_reverse(intersection)
block_ray = get_southwest_ray(bitboard, first_blocker)
south_ray ^= block_ray
# west route
west_ray = get_west_ray(bitboard, move.from_sq)
intersection = occupied & west_ray
if intersection:
first_blocker = bitscan_reverse(intersection)
block_ray = get_southeast_ray(bitboard, first_blocker)
west_ray ^= block_ray
legal_moves = moving_to_square & (north_ray | east_ray | south_ray | west_ray)
occupied_squares = {
Color.BLACK: self.board.black_pieces_bb,
Color.WHITE: self.board.white_pieces_bb,
}
# remove own piece targets
own_piece_targets = occupied_squares[self.color_to_move] & moving_to_square
if own_piece_targets:
legal_moves &= ~own_piece_targets
return legal_moves
def intersects_with_opp_pieces(self, square):
bitboard = make_uint64()
move_square_bb = set_bit(bitboard, square)
occupy_lookup = {
Color.WHITE: self.board.black_pieces_bb,
Color.BLACK: self.board.white_pieces_bb,
}
return occupy_lookup[self.color_to_move] & move_square_bb
def is_legal_knight_move(self, move: Move) -> np.uint64:
bitboard = make_uint64()
legal_knight_moves = self.board.get_knight_attack_from(move.from_sq)
if not legal_knight_moves & set_bit(bitboard, move.to_sq):
return False
# if intersects_with_own_pieces return False
if self.intersects_with_own_pieces(move.to_sq):
return False
# if intersects_with_opp_pieces return True, is_capture => True
if self.intersects_with_opp_pieces(move.to_sq):
move.is_capture = True
return True
return True
def is_legal_pawn_move(self, move: Move) -> bool:
"""
Pseudo-Legal Pawn Moves:
- Pawn non-attacks that don't intersect with occupied squares
- Pawn attacks that intersect with opponent pieces
:param move: the proposed Move instance
:return: True iff Move is legal
"""
bitboard = make_uint64()
moving_to_square = set_bit(bitboard, move.to_sq)
legal_non_attack_moves = {
Color.WHITE: self.board.white_pawn_motion_bbs[move.from_sq],
Color.BLACK: self.board.black_pawn_motion_bbs[move.from_sq]
}
legal_non_attack_moves[self.color_to_move] &= self.board.empty_squares_bb
legal_attack_moves = {
Color.WHITE: self.board.white_pawn_attack_bbs[move.from_sq],
Color.BLACK: self.board.black_pawn_attack_bbs[move.from_sq]
}
opp_occupied = {
Color.WHITE: self.board.black_pieces_bb,
Color.BLACK: self.board.white_pieces_bb
}
legal_attack_moves[self.color_to_move] &= opp_occupied[self.color_to_move]
legal_moves = legal_non_attack_moves[self.color_to_move] | legal_attack_moves[self.color_to_move]
# Handle en-passant targets
if self.en_passant_target:
en_passant_bb = set_bit(bitboard, self.en_passant_target)
en_passant_move = legal_attack_moves[self.color_to_move] & en_passant_bb
legal_moves |= en_passant_move
# Handle Captures
if moving_to_square & legal_attack_moves[self.color_to_move]:
move.is_capture = True
# Handle removing own piece targets
occupied_squares = {
Color.BLACK: self.board.black_pieces_bb,
Color.WHITE: self.board.white_pieces_bb,
}
own_piece_targets = occupied_squares[self.color_to_move] & moving_to_square
if own_piece_targets:
legal_moves &= ~own_piece_targets
# Handle promotion
promotion_rank = {
Color.WHITE: Rank.hex8,
Color.BLACK: Rank.hex1
}
if moving_to_square & promotion_rank[self.color_to_move]:
move.is_promotion = True
return legal_moves & moving_to_square
def __init__(self):
# white piece groups
self.white_R_bb = make_uint64()
self.white_K_bb = make_uint64()
self.white_B_bb = make_uint64()
self.white_P_bb = make_uint64()
self.white_N_bb = make_uint64()
self.white_Q_bb = make_uint64()
# black piece groups
self.black_R_bb = make_uint64()
self.black_K_bb = make_uint64()
self.black_B_bb = make_uint64()
self.black_P_bb = make_uint64()
self.black_N_bb = make_uint64()
self.black_Q_bb = make_uint64()
self.init_pieces()
# static bitboards
self.knight_attack_bbs = make_knight_attack_bbs()
self.bishop_attack_bbs = make_diag_attack_bbs()
self.king_attack_bbs = make_king_attack_bbs()
self.rook_attack_bbs = make_rook_attack_bbs()
self.queen_attack_bbs = make_queen_attack_bbs()
self.white_pawn_attack_bbs = make_white_pawn_attack_bbs()
self.black_pawn_attack_bbs = make_black_pawn_attack_bbs()
self.white_pawn_motion_bbs = make_white_pawn_motion_bbs()
self.black_pawn_motion_bbs = make_black_pawn_motion_bbs()