Chess: Fix signed/unsigned issues

Make everything signed so that we don't have to deal with silly casting
issues thoughout the Chess code. I am unsure if this affects the chess
AI negatively, it seems just as "intelligent" before and after this
change :^)

Userland/Games/Chess/ChessWidget.cpp

@@ -37,7 +37,7 @@ void ChessWidget::paint_event(GUI::PaintEvent& event)
 
     size_t tile_width = frame_inner_rect().width() / 8;
     size_t tile_height = frame_inner_rect().height() / 8;
-    unsigned coord_rank_file = (side() == Chess::Color::White) ? 0 : 7;
+    int coord_rank_file = (side() == Chess::Color::White) ? 0 : 7;
 
     Chess::Board& active_board = (m_playback ? board_playback() : board());
 
@@ -362,13 +362,13 @@ void ChessWidget::set_piece_set(const StringView& set)
 
 Chess::Square ChessWidget::mouse_to_square(GUI::MouseEvent& event) const
 {
-    unsigned tile_width = frame_inner_rect().width() / 8;
+    int tile_width = frame_inner_rect().width() / 8;
-    unsigned tile_height = frame_inner_rect().height() / 8;
+    int tile_height = frame_inner_rect().height() / 8;
 
     if (side() == Chess::Color::White) {
-        return { (unsigned)(7 - (event.y() / tile_height)), (unsigned)(event.x() / tile_width) };
+        return { 7 - (event.y() / tile_height), event.x() / tile_width };
     } else {
-        return { (unsigned)(event.y() / tile_height), (unsigned)(7 - (event.x() / tile_width)) };
+        return { event.y() / tile_height, 7 - (event.x() / tile_width) };
     }
 }
 

Userland/Libraries/LibChess/Chess.cpp

@@ -152,12 +152,12 @@ Move Move::from_algebraic(const StringView& algebraic, const Color turn, const B
                         return IterationDecision::Break;
                     }
                 } else if (move_string.characters()[0] <= 57) {
-                    if (square.rank == (unsigned)(move_string.characters()[0] - '0')) {
+                    if (square.rank == (move_string.characters()[0] - '0')) {
                         move.from = square;
                         return IterationDecision::Break;
                     }
                 } else {
-                    if (square.file == (unsigned)(move_string.characters()[0] - 'a')) {
+                    if (square.file == (move_string.characters()[0] - 'a')) {
                         move.from = square;
                         return IterationDecision::Break;
                     }
@@ -222,19 +222,19 @@ String Move::to_algebraic() const
 Board::Board()
 {
     // Fill empty spaces.
-    for (unsigned rank = 2; rank < 6; ++rank) {
+    for (int rank = 2; rank < 6; ++rank) {
-        for (unsigned file = 0; file < 8; ++file) {
+        for (int file = 0; file < 8; ++file) {
             set_piece({ rank, file }, EmptyPiece);
         }
     }
 
     // Fill white pawns.
-    for (unsigned file = 0; file < 8; ++file) {
+    for (int file = 0; file < 8; ++file) {
         set_piece({ 1, file }, { Color::White, Type::Pawn });
     }
 
     // Fill black pawns.
-    for (unsigned file = 0; file < 8; ++file) {
+    for (int file = 0; file < 8; ++file) {
         set_piece({ 6, file }, { Color::Black, Type::Pawn });
     }
 
@@ -265,8 +265,8 @@ String Board::to_fen() const
 
     // 1. Piece placement
     int empty = 0;
-    for (unsigned rank = 0; rank < 8; rank++) {
+    for (int rank = 0; rank < 8; rank++) {
-        for (unsigned file = 0; file < 8; file++) {
+        for (int file = 0; file < 8; file++) {
             const Piece p(get_piece({ 7 - rank, file }));
             if (p.type == Type::None) {
                 empty++;
@@ -328,15 +328,13 @@ String Board::to_fen() const
 
 Piece Board::get_piece(const Square& square) const
 {
-    VERIFY(square.rank < 8);
+    VERIFY(square.in_bounds());
-    VERIFY(square.file < 8);
     return m_board[square.rank][square.file];
 }
 
 Piece Board::set_piece(const Square& square, const Piece& piece)
 {
-    VERIFY(square.rank < 8);
+    VERIFY(square.in_bounds());
-    VERIFY(square.file < 8);
     return m_board[square.rank][square.file] = piece;
 }
 
@@ -354,7 +352,7 @@ bool Board::is_legal_promotion(const Move& move, Color color) const
         return false;
     }
 
-    unsigned promotion_rank = (color == Color::White) ? 7 : 0;
+    int promotion_rank = (color == Color::White) ? 7 : 0;
 
     if (move.to.rank != promotion_rank && move.promote_to != Type::None) {
         // attempted promotion from invalid rank
@@ -419,13 +417,13 @@ bool Board::is_legal_no_check(const Move& move, Color color) const
         // attempted move of opponent's piece
         return false;
 
-    if (move.to.rank > 7 || move.to.file > 7)
+    if (!move.to.in_bounds())
         // attempted move outside of board
         return false;
 
     if (piece.type == Type::Pawn) {
         int dir = (color == Color::White) ? +1 : -1;
-        unsigned start_rank = (color == Color::White) ? 1 : 6;
+        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) {
@@ -443,8 +441,8 @@ bool Board::is_legal_no_check(const Move& move, Color color) const
         }
 
         if (move.to.file == move.from.file + 1 || move.to.file == move.from.file - 1) {
-            unsigned other_start_rank = (color == Color::White) ? 6 : 1;
+            int other_start_rank = (color == Color::White) ? 6 : 1;
-            unsigned en_passant_rank = (color == Color::White) ? 4 : 3;
+            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.
@@ -843,7 +841,7 @@ bool Board::is_promotion_move(const Move& move, Color color) const
     if (color == Color::None)
         color = turn();
 
-    unsigned promotion_rank = (color == Color::White) ? 7 : 0;
+    int promotion_rank = (color == Color::White) ? 7 : 0;
     if (move.to.rank != promotion_rank)
         return false;
 

Userland/Libraries/LibChess/Chess.h

@@ -55,10 +55,10 @@ struct Piece {
 constexpr Piece EmptyPiece = { Color::None, Type::None };
 
 struct Square {
-    unsigned rank; // zero indexed;
+    int rank; // zero indexed;
-    unsigned file;
+    int file;
     Square(const StringView& name);
-    Square(const unsigned& rank, const unsigned& file)
+    Square(const int& rank, const int& file)
         : rank(rank)
         , file(file)
     {
@@ -76,7 +76,7 @@ struct Square {
         }
     }
 
-    bool in_bounds() const { return rank < 8 && file < 8; }
+    bool in_bounds() const { return rank >= 0 && file >= 0 && rank < 8 && file < 8; }
     bool is_light() const { return (rank % 2) != (file % 2); }
     String to_algebraic() const;
 };