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chess.cpp
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chess.cpp
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#include "chess.h"
chess::chess() :
castle_masks{{{0x6000000000000000, 0x0e00000000000000}, {0x60, 0x0e}}} {
setup_position(start_pos);
}
chess::chess(const std::string &fen) :
castle_masks{{{0x6000000000000000, 0x0e00000000000000}, {0x60, 0x0e}}} {
setup_position(fen);
}
bool chess::setup_position(const std::string &fen) {
return board::setup_position(fen);
}
bool chess::enter_move(const std::string &str) {
const auto move = move_from_str(str);
if (!is_pseudo_legal(move))
return false;
make_move(move);
if (was_legal(move))
return true;
unmake_move();
return false;
}
std::vector<board::move_s> chess::gen_moves() {
std::vector<move_s> moves, tmp_moves;
tmp_moves.reserve(64);
gen_pseudo_legal_moves(tmp_moves);
for (auto m : tmp_moves) {
make_move(m);
if (was_legal(m))
moves.push_back(m);
unmake_move();
}
return moves;
}
void chess::gen_pseudo_legal_moves(std::vector<move_s> &moves,
const gen_mode mode) const {
const u64 occupancy = bb[0][occupancy_ix] | bb[1][occupancy_ix];
const u64 opp_occupancy = bb[!side][occupancy_ix];
gen_pawns(moves, occupancy, opp_occupancy, mode);
gen_non_pawns(moves, knight_ix, occupancy, opp_occupancy, mode);
gen_non_pawns(moves, bishop_ix, occupancy, opp_occupancy, mode);
gen_non_pawns(moves, rook_ix, occupancy, opp_occupancy, mode);
gen_non_pawns(moves, queen_ix, occupancy, opp_occupancy, mode);
gen_non_pawns(moves, king_ix, occupancy, opp_occupancy, mode);
if (mode != gen_mode::only_captures)
gen_castles(moves, occupancy);
}
bool chess::is_in_check(const bool king_side) const {
const u8 king_coord = trail_zeros(bb[king_side][king_ix]);
if (is_attacked_by_non_slider(king_coord, !king_side))
return true;
if (slider_maybe_attacks(king_coord, !king_side)) {
if (is_attacked_by_slider(king_coord, !king_side))
return true;
}
return false;
}
bool chess::is_mate() {
if (!is_in_check(side))
return false;
return gen_moves().size() == 0;
}
bool chess::is_draw() {
return is_N_fold_repetition(2) || is_draw_by_N_move_rule(75) ||
is_stalemate() || is_draw_by_material();
}
bool chess::is_stalemate() {
if (is_in_check(side))
return false;
return gen_moves().size() == 0;
}
bool chess::is_N_fold_repetition(const unsigned N) const {
int cur_ply = int(state_storage.size());
int cur_reverse_cr = reversible_halfmoves;
unsigned repeat_cr = 0;
for (int ply = cur_ply - 2; ply >= 0; ply -= 2) {
if (state_storage[size_t(ply)].reversible_halfmoves >= cur_reverse_cr)
return false;
if (state_storage[size_t(ply)].hash_key == hash_key) {
repeat_cr++;
if (repeat_cr >= N)
return true;
}
}
return false;
}
bool chess::slider_maybe_attacks(const u8 coord,
const bool attacker_side) const {
const bool can_diag = (diag_mask[coord] | antidiag_mask[coord]) &
(bb[attacker_side][bishop_ix] | bb[attacker_side][queen_ix]);
const bool can_rook = (file_mask(coord) | rank_mask(coord)) &
(bb[attacker_side][rook_ix] | bb[attacker_side][queen_ix]);
return can_diag | can_rook;
}
void chess::gen_pawns(std::vector<move_s> &moves, const u64 occupancy,
const u64 opp_occupancy, const gen_mode mode) const {
const u64 pawn_bb = bb[side][pawn_ix];
if (mode != gen_mode::only_captures)
gen_pawns_silent(moves, pawn_bb, occupancy);
if (mode != gen_mode::only_silent)
gen_pawns_captures_and_promotions(moves, pawn_bb, occupancy,
opp_occupancy);
}
void chess::gen_pawns_silent(std::vector<move_s> &moves, const u64 pawn_bb,
const u64 occupancy) const {
const int shift = side == white ? 8 : -8;
const u64 mask = rank_mask(side == white ? '7' : '2');
const u64 pawn_pushes = all_pawn_pushes(pawn_bb & ~mask, side, occupancy);
push_pawn_moves(moves, pawn_pushes, shift, false);
const u64 dbl_pushes = all_pawn_double_pushes(pawn_pushes, side,
occupancy);
push_pawn_moves(moves, dbl_pushes, 2*shift, false);
}
void chess::gen_pawns_captures_and_promotions(std::vector<move_s> &moves,
const u64 pawn_bb,
const u64 occupancy,
u64 opp_occupancy) const {
const int shift = side == white ? 8 : -8;
const u64 mask = rank_mask(side == white ? '7' : '2');
const u64 pawn_pushes = all_pawn_pushes(pawn_bb & mask, side, occupancy);
push_pawn_moves(moves, pawn_pushes, shift, false);
opp_occupancy |= en_passant_bitboard;
const u64 capt_queenside =
all_pawn_attacks_queenside(pawn_bb, side, opp_occupancy);
const auto &shifts_q = pawn_attacks_queenside_shifts;
push_pawn_moves(moves, capt_queenside, -shifts_q[side], true);
const u64 capt_kingside =
all_pawn_attacks_kingside(pawn_bb, side, opp_occupancy);
const auto &shifts_k = pawn_attacks_kingside_shifts;
push_pawn_moves(moves, capt_kingside, -shifts_k[side], true);
}
void chess::push_pawn_moves(std::vector<move_s> &moves, u64 bitboard,
const int shift, const bool is_capt) const {
while (bitboard) {
const u64 lowbit = lower_bit(bitboard);
const u8 to_coord = trail_zeros(lowbit);
const u8 promos[] = {0, queen_ix, rook_ix, knight_ix, bishop_ix};
const u8 row = get_row(to_coord);
const u8 beg = (row == 0 || row == 7) ? 1 : 0;
const u8 end = (row == 0 || row == 7) ? sizeof(promos) : 1;
for (u8 promo = beg; promo < end; ++promo)
moves.push_back({pawn_ix, u8(to_coord - shift),
to_coord, promo, is_capt});
bitboard ^= lowbit;
}
}
void chess::gen_non_pawns(std::vector<move_s> &moves, const u8 piece_index,
const u64 occupancy, const u64 opp_occupancy,
const gen_mode mode) const {
const u64 own_occupancy = occupancy ^ opp_occupancy;
u64 from_bitboard = bb[side][piece_index];
while (from_bitboard) {
const u64 from_lowbit = lower_bit(from_bitboard);
const u8 from_coord = trail_zeros(from_lowbit);
u64 to_bitboard = ~own_occupancy &
all_non_pawn_attacks(piece_index, from_coord, occupancy);
if (mode == gen_mode::only_captures)
to_bitboard &= opp_occupancy;
else if (mode == gen_mode::only_silent)
to_bitboard &= ~opp_occupancy;
while (to_bitboard) {
const u64 to_lowbit = lower_bit(to_bitboard);
moves.push_back({piece_index, from_coord, trail_zeros(to_lowbit),
0, bool(to_lowbit & opp_occupancy)});
to_bitboard ^= to_lowbit;
}
from_bitboard ^= from_lowbit;
}
}
void chess::gen_castles(std::vector<move_s> &moves, const u64 occupancy) const{
const u8 fr_coord[] = {str_to_coord("e8"), str_to_coord("e1")};
const auto &cstl = castling_rights[side];
if (cstl & castle_kingside &&
!(occupancy & castle_masks[side][0]))
moves.push_back({king_ix, fr_coord[side],
u8(fr_coord[side] + 2), 0});
if (cstl & castle_queenside &&
!(occupancy & castle_masks[side][1]))
moves.push_back({king_ix, fr_coord[side],
u8(fr_coord[side] - 2), 0});
}
bool chess::is_attacked_by_slider(const u8 coord,
const bool attacker_side) const {
const u64 occ = bb[0][occupancy_ix] | bb[1][occupancy_ix];
if (rook_attacks(coord, occ) & (bb[attacker_side][rook_ix] |
bb[attacker_side][queen_ix]))
return true;
if (bishop_attacks(coord, occ) & (bb[attacker_side][bishop_ix] |
bb[attacker_side][queen_ix]))
return true;
return false;
}
bool chess::is_attacked_by_non_slider(const u8 coord,
const bool attacker_side) const {
const u64 pawn_bb = bb[attacker_side][pawn_ix];
if (all_pawn_attacks(pawn_bb, attacker_side, u64(-1)) & one_nth_bit(coord))
return true;
if (knight_attacks(coord) & bb[attacker_side][knight_ix])
return true;
if (king_attacks(coord) & bb[attacker_side][king_ix])
return true;
return false;
}
bool chess::castling_was_legal(const bool attacker_side,
const u8 fr_crd, const u8 to_crd) const {
const auto crd1 = fr_crd < to_crd ? fr_crd : to_crd;
const auto crd2 = fr_crd < to_crd ? to_crd : fr_crd;
for (auto coord = crd1; coord <= crd2; ++coord)
if (is_attacked_by_slider(coord, attacker_side) ||
is_attacked_by_non_slider(coord, attacker_side))
return false;
return true;
}
bool chess::is_pseudo_legal(const move_s move) const {
const u8 index = find_index(side, one_nth_bit(move.from_coord));
if (index == u8(-1) || index != move.index)
return false;
if (find_index(side, one_nth_bit(move.to_coord)) != u8(-1))
return false;
const u64 to_bb = one_nth_bit(move.to_coord);
const u64 occ = bb[0][occupancy_ix] | bb[1][occupancy_ix];
u64 opp_occ = bb[!side][occupancy_ix];
if (index == pawn_ix)
opp_occ |= en_passant_bitboard;
if (bool(move.is_capture) != bool(get_nth_bit(opp_occ, move.to_coord)))
return false;
if (index == pawn_ix)
return is_pseudo_legal_pawn(move.from_coord, to_bb);
else if (index == king_ix)
return is_pseudo_legal_king(move.from_coord, move.to_coord);
else
return bool(to_bb & all_non_pawn_attacks(move.index,
move.from_coord, occ));
}
bool chess::is_pseudo_legal_pawn(const u8 from_coord, const u64 to_bb) const {
const u64 pawn_bb = one_nth_bit(from_coord);
const u64 opp_occ = bb[!side][occupancy_ix];
const u64 occ = opp_occ | bb[side][occupancy_ix];
const u64 att = all_pawn_attacks(pawn_bb, side,
opp_occ | en_passant_bitboard);
const u64 psh = all_pawn_pushes(pawn_bb, side, occ);
const u64 dbl = all_pawn_double_pushes(psh, side, occ);
return bool(to_bb & (att | psh | dbl));
}
bool chess::is_pseudo_legal_king(const u8 from_coord, const u8 to_coord) const {
const u64 to_bb = one_nth_bit(to_coord);
if (abs(i8(from_coord) - i8(to_coord)) != 2)
return bool(to_bb & king_attacks(from_coord));
const u64 opp_occ = bb[!side][occupancy_ix];
const u64 occ = opp_occ | bb[side][occupancy_ix];
const u64 mask = from_coord > to_coord ?
castle_queenside : castle_kingside;
if (!(mask & castling_rights[side]))
return false;
return !(occ & castle_masks[side][size_t(mask - 1)]);
}
bool chess::is_draw_by_material() const {
for (auto ix : {pawn_ix, rook_ix, queen_ix})
if (bb[0][ix] || bb[1][ix])
return false;
auto white_bishops = __builtin_popcountll(bb[white][bishop_ix]);
auto black_bishops = __builtin_popcountll(bb[black][bishop_ix]);
auto white_knights = __builtin_popcountll(bb[white][knight_ix]);
auto black_knights = __builtin_popcountll(bb[black][knight_ix]);
return white_bishops + white_knights <= 1 && black_bishops + black_knights <= 1;
}
std::string chess::game_text_result() {
std::string ans;
if (is_mate())
ans = !side ? "1-0 {White mates}" : "0-1 {Black mates";
else if (is_stalemate())
ans = "1/2 - 1/2 {Stalemate}";
else {
ans = "1/2 - 1/2 {Draw by ";
if (is_draw_by_material())
ans += "insufficient mating material}";
else if (is_N_fold_repetition(3 - 1))
ans += "3-fold repetition}";
else
ans += "fifty moves rule";
}
return ans;
}