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ladybird/Userland/Libraries/LibChess/Chess.cpp
Tim Ledbetter ccab25e54e LibChess+Chess: Ensure no pawns have moved when invoking 50 move rule 
The 50 and 75 move rules are no longer invoked if a pawn has advanced
in the last 50 or 75 moves respectively.
2023-05-05 16:56:18 +01:00

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/*
* Copyright (c) 2020, the SerenityOS developers.
* Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Assertions.h>
#include <AK/CharacterTypes.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
#include <AK/Vector.h>
#include <LibChess/Chess.h>
#include <stdlib.h>
namespace Chess {
Optional<char> char_for_piece(Type type, Notation notation)
{
switch (type) {
case Type::Knight:
return 'N';
case Type::Bishop:
return 'B';
case Type::Rook:
return 'R';
case Type::Queen:
return 'Q';
case Type::King:
return 'K';
case Type::Pawn:
if (notation == Notation::FEN)
return 'P';
return {};
case Type::None:
return {};
}
VERIFY_NOT_REACHED();
}
Type piece_from_char(char c)
{
switch (to_ascii_lowercase(c)) {
case 'n':
return Type::Knight;
case 'b':
return Type::Bishop;
case 'r':
return Type::Rook;
case 'q':
return Type::Queen;
case 'k':
return Type::King;
case 'p':
return Type::Pawn;
}
return Type::None;
}
Color opposing_color(Color color)
{
return (color == Color::White) ? Color::Black : Color::White;
}
Square::Square(StringView name)
{
VERIFY(name.length() == 2);
char filec = name[0];
char rankc = name[1];
if (filec >= 'a' && filec <= 'h') {
file = filec - 'a';
} else if (filec >= 'A' && filec <= 'H') {
file = filec - 'A';
} else {
VERIFY_NOT_REACHED();
}
if (rankc >= '1' && rankc <= '8') {
rank = rankc - '1';
} else {
VERIFY_NOT_REACHED();
}
}
char Square::file_char() const
{
return file + 'a';
}
char Square::rank_char() const
{
return rank + '1';
}
ErrorOr<String> Square::to_algebraic() const
{
return String::formatted("{}{}", file_char(), rank_char());
}
Move::Move(StringView long_algebraic)
: from(long_algebraic.substring_view(0, 2))
, to(long_algebraic.substring_view(2, 2))
, promote_to((long_algebraic.length() >= 5) ? piece_from_char(long_algebraic[4]) : Type::None)
{
}
ErrorOr<String> Move::to_long_algebraic() const
{
StringBuilder builder;
TRY(builder.try_append(TRY(from.to_algebraic())));
TRY(builder.try_append(TRY(to.to_algebraic())));
if (auto promoted_char = char_for_piece(promote_to, Notation::Algebraic); promoted_char.has_value())
TRY(builder.try_append(to_ascii_lowercase(promoted_char.value())));
return builder.to_string();
}
Move Move::from_algebraic(StringView algebraic, const Color turn, Board const& board)
{
auto move_string = algebraic;
Move move({ 50, 50 }, { 50, 50 });
if (move_string.contains('-')) {
move.from = Square(turn == Color::White ? 0 : 7, 4);
move.to = Square(turn == Color::White ? 0 : 7, move_string == "O-O" ? 6 : 2);
move.promote_to = Type::None;
move.piece = { turn, Type::King };
return move;
}
if (algebraic.contains('#')) {
move.is_mate = true;
move_string = move_string.substring_view(0, move_string.length() - 1);
} else if (algebraic.contains('+')) {
move.is_check = true;
move_string = move_string.substring_view(0, move_string.length() - 1);
}
if (algebraic.contains('=')) {
auto parts = move_string.split_view('=');
move.promote_to = piece_from_char(parts[1][0]);
move_string = parts[0];
}
move.to = Square(move_string.substring_view(move_string.length() - 2, 2));
move_string = move_string.substring_view(0, move_string.length() - 2);
if (move_string.contains('x')) {
move.is_capture = true;
move_string = move_string.substring_view(0, move_string.length() - 1);
}
if (move_string.is_empty() || move_string[0] >= 'a') {
move.piece = Piece(turn, Type::Pawn);
} else {
move.piece = Piece(turn, piece_from_char(move_string[0]));
move_string = move_string.substring_view(1, move_string.length() - 1);
}
Square::for_each([&](Square const& square) {
if (!move_string.is_empty()) {
if (board.get_piece(square).type == move.piece.type && board.is_legal(Move(square, move.to), turn)) {
if (move_string.length() >= 2) {
if (square == Square(move_string.substring_view(0, 2))) {
move.from = square;
return IterationDecision::Break;
}
} else if (move_string[0] <= 57) {
if (square.rank == (move_string[0] - '0')) {
move.from = square;
return IterationDecision::Break;
}
} else {
if (square.file == (move_string[0] - 'a')) {
move.from = square;
return IterationDecision::Break;
}
}
}
return IterationDecision::Continue;
} else {
if (board.get_piece(square).type == move.piece.type && board.is_legal(Move(square, move.to, move.promote_to), turn)) {
move.from = square;
return IterationDecision::Break;
}
return IterationDecision::Continue;
}
});
return move;
}
ErrorOr<String> Move::to_algebraic() const
{
if (piece.type == Type::King && from.file == 4) {
if (to.file == 2)
return "O-O-O"_short_string;
if (to.file == 6)
return "O-O"_short_string;
}
StringBuilder builder;
if (auto piece_char = char_for_piece(piece.type, Notation::Algebraic); piece_char.has_value())
TRY(builder.try_append(*piece_char));
if (is_ambiguous) {
if (from.file != ambiguous.file)
TRY(builder.try_append(from.file_char()));
else if (from.rank != ambiguous.rank)
TRY(builder.try_append(from.rank_char()));
else
TRY(builder.try_append(TRY(from.to_algebraic())));
}
if (is_capture) {
if (piece.type == Type::Pawn && !is_ambiguous)
TRY(builder.try_append(from.file_char()));
TRY(builder.try_append('x'));
}
TRY(builder.try_append(TRY(to.to_algebraic())));
if (promote_to != Type::None && promote_to != Type::Pawn) {
TRY(builder.try_append('='));
TRY(builder.try_append(char_for_piece(promote_to, Notation::Algebraic).value()));
}
if (is_mate)
TRY(builder.try_append('#'));
else if (is_check)
TRY(builder.try_append('+'));
return builder.to_string();
}
Board::Board()
{
// Fill empty spaces.
for (int rank = 2; rank < 6; ++rank) {
for (int file = 0; file < 8; ++file) {
set_piece({ rank, file }, EmptyPiece);
}
}
// Fill white pawns.
for (int file = 0; file < 8; ++file) {
set_piece({ 1, file }, { Color::White, Type::Pawn });
}
// Fill black pawns.
for (int file = 0; file < 8; ++file) {
set_piece({ 6, file }, { Color::Black, Type::Pawn });
}
// Fill while pieces.
set_piece(Square("a1"), { Color::White, Type::Rook });
set_piece(Square("b1"), { Color::White, Type::Knight });
set_piece(Square("c1"), { Color::White, Type::Bishop });
set_piece(Square("d1"), { Color::White, Type::Queen });
set_piece(Square("e1"), { Color::White, Type::King });
set_piece(Square("f1"), { Color::White, Type::Bishop });
set_piece(Square("g1"), { Color::White, Type::Knight });
set_piece(Square("h1"), { Color::White, Type::Rook });
// Fill black pieces.
set_piece(Square("a8"), { Color::Black, Type::Rook });
set_piece(Square("b8"), { Color::Black, Type::Knight });
set_piece(Square("c8"), { Color::Black, Type::Bishop });
set_piece(Square("d8"), { Color::Black, Type::Queen });
set_piece(Square("e8"), { Color::Black, Type::King });
set_piece(Square("f8"), { Color::Black, Type::Bishop });
set_piece(Square("g8"), { Color::Black, Type::Knight });
set_piece(Square("h8"), { Color::Black, Type::Rook });
}
Board Board::clone_without_history() const
{
// Note: When used in the MCTSTree, the board doesn't need to have all information about previous states.
// It spares a huge amount of memory.
auto result = *this;
result.m_moves.clear();
result.m_previous_states.clear();
return result;
}
ErrorOr<String> Board::to_fen() const
{
StringBuilder builder;
// 1. Piece placement
int empty = 0;
for (int rank = 0; rank < 8; rank++) {
for (int file = 0; file < 8; file++) {
const Piece p(get_piece({ 7 - rank, file }));
if (p.type == Type::None) {
empty++;
continue;
}
if (empty > 0) {
TRY(builder.try_appendff("{}", empty));
empty = 0;
}
auto const piece = char_for_piece(p.type, Notation::FEN).value();
if (p.color == Color::Black)
TRY(builder.try_append(to_ascii_lowercase(piece)));
else
TRY(builder.try_append(piece));
}
if (empty > 0) {
TRY(builder.try_appendff("{}", empty));
empty = 0;
}
if (rank < 7)
TRY(builder.try_append('/'));
}
// 2. Active color
VERIFY(m_turn != Color::None);
TRY(builder.try_append(m_turn == Color::White ? " w "sv : " b "sv));
// 3. Castling availability
if (m_white_can_castle_kingside)
TRY(builder.try_append('K'));
if (m_white_can_castle_queenside)
TRY(builder.try_append('Q'));
if (m_black_can_castle_kingside)
TRY(builder.try_append('k'));
if (m_black_can_castle_queenside)
TRY(builder.try_append('q'));
TRY(builder.try_append(' '));
// 4. En passant target square
if (!m_last_move.has_value())
TRY(builder.try_append('-'));
else if (m_last_move.value().piece.type == Type::Pawn) {
if (m_last_move.value().from.rank == 1 && m_last_move.value().to.rank == 3)
TRY(builder.try_append(TRY(Square(m_last_move.value().to.rank - 1, m_last_move.value().to.file).to_algebraic())));
else if (m_last_move.value().from.rank == 6 && m_last_move.value().to.rank == 4)
TRY(builder.try_append(TRY(Square(m_last_move.value().to.rank + 1, m_last_move.value().to.file).to_algebraic())));
else
TRY(builder.try_append('-'));
} else {
TRY(builder.try_append('-'));
}
TRY(builder.try_append(' '));
// 5. Halfmove clock
TRY(builder.try_appendff("{}", (min(m_moves_since_capture, m_moves_since_pawn_advance))));
TRY(builder.try_append(' '));
// 6. Fullmove number
TRY(builder.try_appendff("{}", (1 + m_moves.size() / 2)));
return builder.to_string();
}
Piece Board::get_piece(Square const& square) const
{
VERIFY(square.in_bounds());
return m_board[square.rank][square.file];
}
Piece Board::set_piece(Square const& square, Piece const& piece)
{
VERIFY(square.in_bounds());
return m_board[square.rank][square.file] = piece;
}
bool Board::is_legal_promotion(Move const& move, Color color) const
{
auto piece = get_piece(move.from);
if (move.promote_to == Type::Pawn || move.promote_to == Type::King) {
// attempted promotion to invalid piece
return false;
}
if (piece.type != Type::Pawn && move.promote_to != Type::None) {
// attempted promotion from invalid piece
return false;
}
int promotion_rank = (color == Color::White) ? 7 : 0;
if (move.to.rank != promotion_rank && move.promote_to != Type::None) {
// attempted promotion from invalid rank
return false;
}
if (piece.type == Type::Pawn && move.to.rank == promotion_rank && move.promote_to == Type::None) {
// attempted move to promotion rank without promoting
return false;
}
return true;
}
bool Board::is_legal(Move const& move, Color color) const
{
if (color == Color::None)
color = turn();
if (!is_legal_no_check(move, color))
return false;
if (!is_legal_promotion(move, color))
return false;
Board clone = *this;
clone.apply_illegal_move(move, color);
if (clone.in_check(color))
return false;
// Don't allow castling through check or out of check.
Vector<Square> check_squares;
if (color == Color::White && move.from == Square("e1") && get_piece(Square("e1")) == Piece(Color::White, Type::King)) {
if (move.to == Square("a1") || move.to == Square("c1")) {
check_squares = { Square("e1"), Square("d1"), Square("c1") };
} else if (move.to == Square("h1") || move.to == Square("g1")) {
check_squares = { Square("e1"), Square("f1"), Square("g1") };
}
} else if (color == Color::Black && move.from == Square("e8") && get_piece(Square("e8")) == Piece(Color::Black, Type::King)) {
if (move.to == Square("a8") || move.to == Square("c8")) {
check_squares = { Square("e8"), Square("d8"), Square("c8") };
} else if (move.to == Square("h8") || move.to == Square("g8")) {
check_squares = { Square("e8"), Square("f8"), Square("g8") };
}
}
for (auto& square : check_squares) {
Board clone = *this;
clone.set_piece(move.from, EmptyPiece);
clone.set_piece(square, { color, Type::King });
if (clone.in_check(color))
return false;
}
return true;
}
bool Board::is_legal_no_check(Move const& move, Color color) const
{
auto piece = get_piece(move.from);
if (piece.color != color)
// attempted move of opponent's piece
return false;
if (!move.to.in_bounds())
// attempted move outside of board
return false;
// Check castling first to allow dragging king onto the rook.
if (piece.type == Type::King) {
if (color == Color::White) {
if ((move.to == Square("a1") || move.to == Square("c1")) && m_white_can_castle_queenside && get_piece(Square("b1")).type == Type::None && get_piece(Square("c1")).type == Type::None && get_piece(Square("d1")).type == Type::None) {
return true;
} else if ((move.to == Square("h1") || move.to == Square("g1")) && m_white_can_castle_kingside && get_piece(Square("f1")).type == Type::None && get_piece(Square("g1")).type == Type::None) {
return true;
}
} else {
if ((move.to == Square("a8") || move.to == Square("c8")) && m_black_can_castle_queenside && get_piece(Square("b8")).type == Type::None && get_piece(Square("c8")).type == Type::None && get_piece(Square("d8")).type == Type::None) {
return true;
} else if ((move.to == Square("h8") || move.to == Square("g8")) && m_black_can_castle_kingside && get_piece(Square("f8")).type == Type::None && get_piece(Square("g8")).type == Type::None) {
return true;
}
}
}
if (piece.color == get_piece(move.to).color)
// Attempted move to a square occupied by a piece of the same color.
return false;
if (piece.type == Type::Pawn) {
int dir = (color == Color::White) ? +1 : -1;
int start_rank = (color == Color::White) ? 1 : 6;
if (move.from.rank == start_rank && move.to.rank == move.from.rank + (2 * dir) && move.to.file == move.from.file
&& get_piece(move.to).type == Type::None && get_piece({ move.from.rank + dir, move.from.file }).type == Type::None) {
// 2 square pawn move from initial position.
return true;
}
if (move.to.rank != move.from.rank + dir)
// attempted backwards or sideways move
return false;
if (move.to.file == move.from.file && get_piece(move.to).type == Type::None) {
// Regular pawn move.
return true;
}
if (move.to.file == move.from.file + 1 || move.to.file == move.from.file - 1) {
int other_start_rank = (color == Color::White) ? 6 : 1;
int en_passant_rank = (color == Color::White) ? 4 : 3;
Move en_passant_last_move = { { other_start_rank, move.to.file }, { en_passant_rank, move.to.file } };
if (get_piece(move.to).color == opposing_color(color)) {
// Pawn capture.
return true;
}
if (m_last_move.has_value() && move.from.rank == en_passant_rank && m_last_move.value() == en_passant_last_move
&& get_piece(en_passant_last_move.to) == Piece(opposing_color(color), Type::Pawn)) {
// En passant.
return true;
}
}
return false;
} else if (piece.type == Type::Knight) {
int rank_delta = abs(move.to.rank - move.from.rank);
int file_delta = abs(move.to.file - move.from.file);
if (max(rank_delta, file_delta) == 2 && min(rank_delta, file_delta) == 1) {
return true;
}
} else if (piece.type == Type::Bishop) {
int rank_delta = move.to.rank - move.from.rank;
int file_delta = move.to.file - move.from.file;
if (abs(rank_delta) == abs(file_delta)) {
int dr = rank_delta / abs(rank_delta);
int df = file_delta / abs(file_delta);
for (Square sq = move.from; sq != move.to; sq.rank += dr, sq.file += df) {
if (get_piece(sq).type != Type::None && sq != move.from) {
return false;
}
}
return true;
}
} else if (piece.type == Type::Rook) {
int rank_delta = move.to.rank - move.from.rank;
int file_delta = move.to.file - move.from.file;
if (rank_delta == 0 || file_delta == 0) {
int dr = (rank_delta) ? rank_delta / abs(rank_delta) : 0;
int df = (file_delta) ? file_delta / abs(file_delta) : 0;
for (Square sq = move.from; sq != move.to; sq.rank += dr, sq.file += df) {
if (get_piece(sq).type != Type::None && sq != move.from) {
return false;
}
}
return true;
}
} else if (piece.type == Type::Queen) {
int rank_delta = move.to.rank - move.from.rank;
int file_delta = move.to.file - move.from.file;
if (abs(rank_delta) == abs(file_delta) || rank_delta == 0 || file_delta == 0) {
int dr = (rank_delta) ? rank_delta / abs(rank_delta) : 0;
int df = (file_delta) ? file_delta / abs(file_delta) : 0;
for (Square sq = move.from; sq != move.to; sq.rank += dr, sq.file += df) {
if (get_piece(sq).type != Type::None && sq != move.from) {
return false;
}
}
return true;
}
} else if (piece.type == Type::King) {
int rank_delta = move.to.rank - move.from.rank;
int file_delta = move.to.file - move.from.file;
if (abs(rank_delta) <= 1 && abs(file_delta) <= 1) {
return true;
}
}
return false;
}
bool Board::in_check(Color color) const
{
Square king_square = { 50, 50 };
Square::for_each([&](Square const& square) {
if (get_piece(square) == Piece(color, Type::King)) {
king_square = square;
return IterationDecision::Break;
}
return IterationDecision::Continue;
});
bool check = false;
Square::for_each([&](Square const& square) {
if (is_legal_no_check({ square, king_square }, opposing_color(color))) {
check = true;
return IterationDecision::Break;
}
return IterationDecision::Continue;
});
return check;
}
bool Board::apply_move(Move const& move, Color color)
{
if (color == Color::None)
color = turn();
if (!is_legal(move, color))
return false;
const_cast<Move&>(move).piece = get_piece(move.from);
return apply_illegal_move(move, color);
}
bool Board::apply_illegal_move(Move const& move, Color color)
{
auto state = Traits<Board>::hash(*this);
auto state_count = 0;
if (m_previous_states.contains(state))
state_count = m_previous_states.get(state).value();
m_previous_states.set(state, state_count + 1);
m_moves.append(move);
m_turn = opposing_color(color);
m_last_move = move;
m_moves_since_capture++;
m_moves_since_pawn_advance++;
if (move.from == Square("a1") || move.to == Square("a1") || move.from == Square("e1"))
m_white_can_castle_queenside = false;
if (move.from == Square("h1") || move.to == Square("h1") || move.from == Square("e1"))
m_white_can_castle_kingside = false;
if (move.from == Square("a8") || move.to == Square("a8") || move.from == Square("e8"))
m_black_can_castle_queenside = false;
if (move.from == Square("h8") || move.to == Square("h8") || move.from == Square("e8"))
m_black_can_castle_kingside = false;
if (color == Color::White && move.from == Square("e1") && get_piece(Square("e1")) == Piece(Color::White, Type::King)) {
if (move.to == Square("a1") || move.to == Square("c1")) {
set_piece(Square("e1"), EmptyPiece);
set_piece(Square("a1"), EmptyPiece);
set_piece(Square("c1"), { Color::White, Type::King });
set_piece(Square("d1"), { Color::White, Type::Rook });
return true;
} else if (move.to == Square("h1") || move.to == Square("g1")) {
set_piece(Square("e1"), EmptyPiece);
set_piece(Square("h1"), EmptyPiece);
set_piece(Square("g1"), { Color::White, Type::King });
set_piece(Square("f1"), { Color::White, Type::Rook });
return true;
}
} else if (color == Color::Black && move.from == Square("e8") && get_piece(Square("e8")) == Piece(Color::Black, Type::King)) {
if (move.to == Square("a8") || move.to == Square("c8")) {
set_piece(Square("e8"), EmptyPiece);
set_piece(Square("a8"), EmptyPiece);
set_piece(Square("c8"), { Color::Black, Type::King });
set_piece(Square("d8"), { Color::Black, Type::Rook });
return true;
} else if (move.to == Square("h8") || move.to == Square("g8")) {
set_piece(Square("e8"), EmptyPiece);
set_piece(Square("h8"), EmptyPiece);
set_piece(Square("g8"), { Color::Black, Type::King });
set_piece(Square("f8"), { Color::Black, Type::Rook });
return true;
}
}
if (move.piece.type == Type::Pawn)
m_moves_since_pawn_advance = 0;
if (get_piece(move.to).color != Color::None) {
const_cast<Move&>(move).is_capture = true;
m_moves_since_capture = 0;
}
if (get_piece(move.from).type == Type::Pawn && ((color == Color::Black && move.to.rank == 0) || (color == Color::White && move.to.rank == 7))) {
// Pawn Promotion
set_piece(move.to, { color, move.promote_to });
set_piece(move.from, EmptyPiece);
if (in_check(m_turn))
const_cast<Move&>(move).is_check = true;
return true;
}
if (get_piece(move.from).type == Type::Pawn && move.from.file != move.to.file && get_piece(move.to).type == Type::None) {
// En passant.
if (color == Color::White) {
set_piece({ move.to.rank - 1, move.to.file }, EmptyPiece);
} else {
set_piece({ move.to.rank + 1, move.to.file }, EmptyPiece);
}
const_cast<Move&>(move).is_capture = true;
m_moves_since_capture = 0;
}
Square::for_each([&](Square sq) {
// Ambiguous Move
if (sq != move.from && get_piece(sq).type == move.piece.type && get_piece(sq).color == move.piece.color) {
if (is_legal(Move(sq, move.to), get_piece(sq).color)) {
m_moves.last().is_ambiguous = true;
m_moves.last().ambiguous = sq;
return IterationDecision::Break;
}
}
return IterationDecision::Continue;
});
set_piece(move.to, get_piece(move.from));
set_piece(move.from, EmptyPiece);
if (in_check(m_turn))
const_cast<Move&>(move).is_check = true;
return true;
}
Move Board::random_move(Color color) const
{
if (color == Color::None)
color = turn();
Move move = { { 50, 50 }, { 50, 50 } };
int probability = 1;
generate_moves([&](Move m) {
if (rand() % probability == 0)
move = m;
++probability;
return IterationDecision::Continue;
});
return move;
}
Board::Result Board::game_result() const
{
if (m_resigned != Color::None)
return (m_resigned == Color::White) ? Result::WhiteResign : Result::BlackResign;
bool sufficient_material = false;
bool no_more_pieces_allowed = false;
Optional<Square> bishop;
Square::for_each([&](Square sq) {
if (get_piece(sq).type == Type::Queen || get_piece(sq).type == Type::Rook || get_piece(sq).type == Type::Pawn) {
sufficient_material = true;
return IterationDecision::Break;
}
if (get_piece(sq).type != Type::None && get_piece(sq).type != Type::King && no_more_pieces_allowed) {
sufficient_material = true;
return IterationDecision::Break;
}
if (get_piece(sq).type == Type::Knight)
no_more_pieces_allowed = true;
if (get_piece(sq).type == Type::Bishop) {
if (bishop.has_value()) {
if (get_piece(sq).color == get_piece(bishop.value()).color) {
sufficient_material = true;
return IterationDecision::Break;
} else if (sq.is_light() != bishop.value().is_light()) {
sufficient_material = true;
return IterationDecision::Break;
}
no_more_pieces_allowed = true;
} else {
bishop = sq;
}
}
return IterationDecision::Continue;
});
if (!sufficient_material)
return Result::InsufficientMaterial;
bool are_legal_moves = false;
generate_moves([&]([[maybe_unused]] Move m) {
are_legal_moves = true;
return IterationDecision::Break;
});
if (are_legal_moves) {
if (m_moves_since_capture >= 75 * 2 && m_moves_since_pawn_advance >= 75 * 2)
return Result::SeventyFiveMoveRule;
if ((m_moves_since_capture >= 50 * 2 && m_moves_since_pawn_advance == 50 * 2)
|| (m_moves_since_pawn_advance >= 50 * 2 && m_moves_since_capture == 50 * 2))
return Result::FiftyMoveRule;
auto repeats = m_previous_states.get(Traits<Board>::hash(*this));
if (repeats.has_value()) {
if (repeats.value() == 3)
return Result::ThreeFoldRepetition;
if (repeats.value() >= 5)
return Result::FiveFoldRepetition;
}
return Result::NotFinished;
}
if (in_check(turn())) {
const_cast<Vector<Move>&>(m_moves).last().is_mate = true;
return Result::CheckMate;
}
return Result::StaleMate;
}
Color Board::game_winner() const
{
if (game_result() == Result::CheckMate)
return opposing_color(turn());
return Color::None;
}
int Board::game_score() const
{
switch (game_winner()) {
case Color::White:
return +1;
case Color::Black:
return -1;
case Color::None:
return 0;
}
return 0;
}
bool Board::game_finished() const
{
return game_result() != Result::NotFinished;
}
int Board::material_imbalance() const
{
int imbalance = 0;
Square::for_each([&](Square square) {
int value = 0;
switch (get_piece(square).type) {
case Type::Pawn:
value = 1;
break;
case Type::Knight:
case Type::Bishop:
value = 3;
break;
case Type::Rook:
value = 5;
break;
case Type::Queen:
value = 9;
break;
default:
break;
}
if (get_piece(square).color == Color::White) {
imbalance += value;
} else {
imbalance -= value;
}
return IterationDecision::Continue;
});
return imbalance;
}
bool Board::is_promotion_move(Move const& move, Color color) const
{
if (color == Color::None)
color = turn();
int promotion_rank = (color == Color::White) ? 7 : 0;
if (move.to.rank != promotion_rank)
return false;
if (get_piece(move.from).type != Type::Pawn)
return false;
Move queen_move = move;
queen_move.promote_to = Type::Queen;
if (!is_legal(queen_move, color))
return false;
return true;
}
bool Board::operator==(Board const& other) const
{
bool equal_squares = true;
Square::for_each([&](Square sq) {
if (get_piece(sq) != other.get_piece(sq)) {
equal_squares = false;
return IterationDecision::Break;
}
return IterationDecision::Continue;
});
if (!equal_squares)
return false;
if (m_white_can_castle_queenside != other.m_white_can_castle_queenside)
return false;
if (m_white_can_castle_kingside != other.m_white_can_castle_kingside)
return false;
if (m_black_can_castle_queenside != other.m_black_can_castle_queenside)
return false;
if (m_black_can_castle_kingside != other.m_black_can_castle_kingside)
return false;
return turn() == other.turn();
}
void Board::set_resigned(Chess::Color c)
{
m_resigned = c;
}
StringView Board::result_to_string(Result result, Color turn)
{
switch (result) {
case Result::CheckMate:
VERIFY(turn != Chess::Color::None);
return turn == Chess::Color::White ? "Black wins by Checkmate"sv : "White wins by Checkmate"sv;
case Result::WhiteResign:
return "Black wins by Resignation"sv;
case Result::BlackResign:
return "White wins by Resignation"sv;
case Result::StaleMate:
return "Draw by Stalemate"sv;
case Chess::Board::Result::FiftyMoveRule:
return "Draw by 50 move rule"sv;
case Chess::Board::Result::SeventyFiveMoveRule:
return "Draw by 75 move rule"sv;
case Chess::Board::Result::ThreeFoldRepetition:
return "Draw by threefold repetition"sv;
case Chess::Board::Result::FiveFoldRepetition:
return "Draw by fivefold repetition"sv;
case Chess::Board::Result::InsufficientMaterial:
return "Draw by insufficient material"sv;
case Chess::Board::Result::NotFinished:
return "Game not finished"sv;
default:
VERIFY_NOT_REACHED();
}
}
StringView Board::result_to_points_string(Result result, Color turn)
{
switch (result) {
case Result::CheckMate:
VERIFY(turn != Chess::Color::None);
return turn == Chess::Color::White ? "0-1"sv : "1-0"sv;
case Result::WhiteResign:
return "0-1"sv;
case Result::BlackResign:
return "1-0"sv;
case Result::StaleMate:
case Chess::Board::Result::FiftyMoveRule:
case Chess::Board::Result::SeventyFiveMoveRule:
case Chess::Board::Result::ThreeFoldRepetition:
case Chess::Board::Result::FiveFoldRepetition:
case Chess::Board::Result::InsufficientMaterial:
return "1/2-1/2"sv;
case Chess::Board::Result::NotFinished:
return "*"sv;
default:
VERIFY_NOT_REACHED();
}
}
}
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