assert(pos.piece_on(ksq) == king_of_color(us));
- // Generate evasions for king
- Bitboard b1 = pos.piece_attacks<KING>(ksq) & ~pos.pieces_of_color(us);
+ // The bitboard of occupied pieces without our king
Bitboard b2 = pos.occupied_squares();
clear_bit(&b2, ksq);
+ // Find squares attacked by slider checkers, we will
+ // remove them from king evasions set so to avoid a couple
+ // of cycles in the slow king evasions legality check loop.
+ Bitboard checkers = pos.checkers();
+ Bitboard checkersAttacks = EmptyBoardBB;
+ Bitboard b = checkers & (pos.queens() | pos.bishops());
+ while (b)
+ {
+ from = pop_1st_bit(&b);
+ checkersAttacks |= bishop_attacks_bb(from, b2);
+ }
+
+ b = checkers & (pos.queens() | pos.rooks());
+ while (b)
+ {
+ from = pop_1st_bit(&b);
+ checkersAttacks |= rook_attacks_bb(from, b2);
+ }
+
+ // Generate evasions for king
+ Bitboard b1 = pos.piece_attacks<KING>(ksq) & ~pos.pieces_of_color(us) & ~checkersAttacks;
while (b1)
{
- to = pop_1st_bit(&b1);
-
- // Make sure 'to' is not attacked by the other side. This is a bit ugly,
- // because we can't use Position::square_is_attacked. Instead we use
- // the low-level bishop_attacks_bb and rook_attacks_bb with the bitboard
- // b2 (the occupied squares with the king removed) in order to test whether
- // the king will remain in check on the destination square.
- if (!( (pos.piece_attacks<KNIGHT>(to) & pos.knights(them))
- || (pos.pawn_attacks(us, to) & pos.pawns(them))
- || (bishop_attacks_bb(to, b2) & pos.bishops_and_queens(them))
- || (rook_attacks_bb(to, b2) & pos.rooks_and_queens(them))
- || (pos.piece_attacks<KING>(to) & pos.kings(them))))
-
- (*mlist++).move = make_move(ksq, to);
+ to = pop_1st_bit(&b1);
+
+ // Make sure 'to' is not attacked by the other side. This is a bit ugly,
+ // because we can't use Position::square_is_attacked. Instead we use
+ // the low-level bishop_attacks_bb and rook_attacks_bb with the bitboard
+ // b2 (the occupied squares with the king removed) in order to test whether
+ // the king will remain in check on the destination square.
+ if (!( (pos.piece_attacks<KNIGHT>(to) & pos.knights(them))
+ || (pos.pawn_attacks(us, to) & pos.pawns(them))
+ || (bishop_attacks_bb(to, b2) & pos.bishops_and_queens(them))
+ || (rook_attacks_bb(to, b2) & pos.rooks_and_queens(them))
+ || (pos.piece_attacks<KING>(to) & pos.kings(them))))
+ (*mlist++).move = make_move(ksq, to);
}
// Generate evasions for other pieces only if not double check. We use a
// simple bit twiddling hack here rather than calling count_1s in order to
// save some time (we know that pos.checkers() has at most two nonzero bits).
- Bitboard checkers = pos.checkers();
-
if (!(checkers & (checkers - 1))) // Only one bit set?
{
Square checksq = first_1(checkers);