--- a/src/chess/rules.c Sat Sep 05 12:36:04 2026 +0200
+++ b/src/chess/rules.c Sat Sep 05 13:03:09 2026 +0200
@@ -144,7 +144,242 @@
}
}
-static bool check_stalemate(const GameState *gamestate) {
+
+/* applies the move without recalculating gamestate flags */
+static void apply_move_internal(GameState *gamestate, Move *move) {
+ /* en passant capture */
+ if (move->capture && piece_type(move->piece) == PAWN &&
+ piece_at(gamestate, move->tofile, move->torank) == 0) {
+ piece_remove(gamestate, move->tofile, move->fromrank);
+ }
+
+ /* remove old en passant threats */
+ for (File file = 0 ; file < 8 ; file++) {
+ enpassant_threat_remove(gamestate, file, 3);
+ enpassant_threat_remove(gamestate, file, 4);
+ }
+
+ /* move (and maybe capture or promote) */
+ piece_remove(gamestate, move->fromfile, move->fromrank);
+ if (move->promotion) {
+ piece_set(gamestate, move->tofile, move->torank, move->promotion);
+ } else {
+ piece_set(gamestate, move->tofile, move->torank, move->piece);
+ }
+
+ /* add new en passant threat */
+ if (piece_type(move->piece) == PAWN && (
+ (move->fromrank == 1 && move->torank == 3) ||
+ (move->fromrank == 6 && move->torank == 4))) {
+ enpassant_threat_add(gamestate, move->tofile, move->torank);
+ }
+
+ /* castling */
+ bool castling_happend = false;
+ if (piece_type(move->piece) == KING && move->fromfile == fileidx('e')) {
+ const Color color = piece_color(move->piece);
+ if (move->tofile == fileidx('g')) {
+ gamestate->board[move->torank][fileidx('h')] = 0;
+ gamestate->board[move->torank][fileidx('f')] = mkpiece(ROOK, color);
+ castling_happend = true;
+ } else if (move->tofile == fileidx('c')) {
+ gamestate->board[move->torank][fileidx('a')] = 0;
+ gamestate->board[move->torank][fileidx('d')] = mkpiece(ROOK, color);
+ castling_happend = true;
+ }
+ }
+ if (castling_happend) {
+ if (piece_color(move->piece) == WHITE) {
+ gamestate->castling.K = true;
+ gamestate->castling.Q = true;
+ } else {
+ gamestate->castling.k = true;
+ gamestate->castling.q = true;
+ }
+ } else {
+ if (piece_color(move->piece) == WHITE) {
+ if (move->fromrank == rankidx('1')) {
+ if (move->fromfile == fileidx('e')) {
+ gamestate->castling.K = gamestate->castling.Q = true;
+ } else if (move->fromfile == fileidx('h')) {
+ gamestate->castling.K = true;
+ } else if (move->fromfile == fileidx('a')) {
+ gamestate->castling.Q = true;
+ }
+ }
+ } else {
+ if (move->fromrank == rankidx('8')) {
+ if (move->fromfile == fileidx('e')) {
+ gamestate->castling.k = gamestate->castling.q = true;
+ } else if (move->fromfile == fileidx('h')) {
+ gamestate->castling.k = true;
+ } else if (move->fromfile == fileidx('a')) {
+ gamestate->castling.q = true;
+ }
+ }
+ }
+ }
+
+ /* add move to the moves array and the new position to the FEN array */
+ if (gamestate->movecount == gamestate->movecapacity) {
+ gamestate->movecapacity += 64; /* 32 more full moves */
+ gamestate->moves = realloc(gamestate->moves,
+ gamestate->movecapacity * sizeof(Move));
+ gamestate->fen = realloc(gamestate->fen,
+ gamestate->movecapacity * sizeof(char*));
+ }
+
+ /* copy the move data into the game's move array */
+ Move *melem = &gamestate->moves[gamestate->movecount];
+ *melem = *move;
+ calc_movetime(gamestate, melem);
+
+ /* important: only "add" the move after calculating the time! */
+ gamestate->movecount++;
+
+ /* calculate the FEN of the new position and store it in the FEN array */
+ char fen[FEN_MAX_LENGTH];
+ fen_compute(fen, gamestate);
+ gamestate->fen[gamestate->movecount - 1] = strdup(fen);
+}
+
+/* return 0 = no check, 1 = check, 2 = checkmate */
+static int determine_check_or_checkmate(
+ const GameState *gamestate, const Move *move) {
+
+ /* either simulate one more move or check for current state */
+ Color piececolor, oppcolor;
+ GameState simulation = gamestate_copy_sim(gamestate);
+ if (move != NULL) {
+ piececolor = piece_color(move->piece);
+ oppcolor = opponent_color(piececolor);
+ Move simmove = *move;
+ apply_move_internal(&simulation, &simmove);
+ } else {
+ oppcolor = current_color(gamestate);
+ piececolor = opponent_color(oppcolor);
+ }
+
+ /* find the opposing king */
+ File opkingfile = 0;
+ Rank opkingrank = 0;
+ for (Rank rank = 0 ; rank < 8 ; rank++) {
+ for (File file = 0 ; file < 8 ; file++) {
+ Piece p = piece_at(&simulation, file, rank);
+ if (p == mkpiece(KING, oppcolor)) {
+ opkingfile = file;
+ opkingrank = rank;
+ }
+ }
+ }
+
+ /* determine if the opposing king is now threatened */
+ Move threats[16];
+ size_t threatcount;
+ bool incheck = get_threats(&simulation, opkingfile, opkingrank,
+ piececolor, threats, &threatcount);
+
+ if (!incheck) {
+ gamestate_cleanup(&simulation);
+ return 0;
+ }
+
+ /* determine possible escape fields */
+ bool canescape = false;
+ for (int dr = -1 ; dr <= 1 && !canescape ; dr++) {
+ for (int df = -1 ; df <= 1 && !canescape ; df++) {
+ if (dr == 0 && df == 0) continue;
+ Rank er = opkingrank + dr;
+ File ef = opkingfile + df;
+ if (!isidx(er) || !isidx(ef)) continue;
+
+ /* check if piece of the king's color blocks the field */
+ if (piece_color(simulation.board[er][ef]) == oppcolor)
+ continue;
+
+ /* check if escape field is already covered (threatened) */
+ if (is_covered(&simulation, ef, er, piececolor))
+ continue;
+
+ /* check if an attacking piece blocks the field */
+ if (piece_color(simulation.board[er][ef]) == piececolor) {
+ /* test if the king can fight back */
+ GameState sim_retaliate = gamestate_copy_sim(&simulation);
+ Move move_retaliate = {0};
+ move_retaliate.piece = mkpiece(KING, oppcolor);
+ move_retaliate.fromrank = opkingrank;
+ move_retaliate.fromfile = opkingfile;
+ move_retaliate.torank = er;
+ move_retaliate.tofile = ef;
+ move_retaliate.capture = true;
+ apply_move_internal(&sim_retaliate, &move_retaliate);
+ canescape = !is_covered(&sim_retaliate, ef, er, piececolor);
+ gamestate_cleanup(&sim_retaliate);
+ continue;
+ }
+
+ /* the field is not covered and unoccupied */
+ canescape = true;
+ }
+ }
+
+ /* can't escape, can the king be rescued? */
+ if (!canescape && threatcount == 1) {
+ canescape = is_protected(&simulation,
+ threats[0].fromfile, threats[0].fromrank, oppcolor);
+ }
+
+ /* can't capture, can he block? */
+ if (!canescape && threatcount == 1) {
+ Move *threat = &(threats[0]);
+ unsigned tptype = piece_type(threat->piece);
+
+ /* knight, pawns and the king cannot be blocked */
+ if (tptype == BISHOP || tptype == ROOK || tptype == QUEEN) {
+ if (threat->fromrank == threat->torank) {
+ /* rook aspect (on rank) */
+ int d = threat->tofile > threat->fromfile ? 1 : -1;
+ File file = threat->fromfile;
+ while (!canescape && file != threat->tofile - d) {
+ file += d;
+ canescape |= is_protected(&simulation,
+ file, threat->torank, oppcolor);
+ }
+ } else if (threat->fromfile == threat->tofile) {
+ /* rook aspect (on file) */
+ int d = threat->torank > threat->fromrank ? 1 : -1;
+ Rank rank = threat->fromrank;
+ while (!canescape && rank != threat->torank - d) {
+ rank += d;
+ canescape |= is_protected(&simulation,
+ threat->tofile, rank, oppcolor);
+ }
+ } else {
+ /* bishop aspect */
+ int dr = threat->torank > threat->fromrank ? 1 : -1;
+ int df = threat->tofile > threat->fromfile ? 1 : -1;
+
+ Rank rank = threat->fromrank;
+ File file = threat->fromfile;
+ while (!canescape && file != threat->tofile - df
+ && rank != threat->torank - dr) {
+ rank += dr;
+ file += df;
+ canescape |= is_protected(&simulation,
+ file, rank, oppcolor);
+ }
+ }
+ }
+ }
+ gamestate_cleanup(&simulation);
+ return canescape ? 1 : 2;
+}
+
+bool check_checkmate(const GameState *gamestate) {
+ return determine_check_or_checkmate(gamestate, NULL) == 2;
+}
+
+bool check_stalemate(const GameState *gamestate) {
Color next_player = current_color(gamestate);
/* scan the board for pieces of the next player's color */
@@ -313,104 +548,6 @@
}
}
-/* applies the move without recalculating gamestate flags */
-static void apply_move_internal(GameState *gamestate, Move *move) {
- /* en passant capture */
- if (move->capture && piece_type(move->piece) == PAWN &&
- piece_at(gamestate, move->tofile, move->torank) == 0) {
- piece_remove(gamestate, move->tofile, move->fromrank);
- }
-
- /* remove old en passant threats */
- for (File file = 0 ; file < 8 ; file++) {
- enpassant_threat_remove(gamestate, file, 3);
- enpassant_threat_remove(gamestate, file, 4);
- }
-
- /* move (and maybe capture or promote) */
- piece_remove(gamestate, move->fromfile, move->fromrank);
- if (move->promotion) {
- piece_set(gamestate, move->tofile, move->torank, move->promotion);
- } else {
- piece_set(gamestate, move->tofile, move->torank, move->piece);
- }
-
- /* add new en passant threat */
- if (piece_type(move->piece) == PAWN && (
- (move->fromrank == 1 && move->torank == 3) ||
- (move->fromrank == 6 && move->torank == 4))) {
- enpassant_threat_add(gamestate, move->tofile, move->torank);
- }
-
- /* castling */
- bool castling_happend = false;
- if (piece_type(move->piece) == KING && move->fromfile == fileidx('e')) {
- const Color color = piece_color(move->piece);
- if (move->tofile == fileidx('g')) {
- gamestate->board[move->torank][fileidx('h')] = 0;
- gamestate->board[move->torank][fileidx('f')] = mkpiece(ROOK, color);
- castling_happend = true;
- } else if (move->tofile == fileidx('c')) {
- gamestate->board[move->torank][fileidx('a')] = 0;
- gamestate->board[move->torank][fileidx('d')] = mkpiece(ROOK, color);
- castling_happend = true;
- }
- }
- if (castling_happend) {
- if (piece_color(move->piece) == WHITE) {
- gamestate->castling.K = true;
- gamestate->castling.Q = true;
- } else {
- gamestate->castling.k = true;
- gamestate->castling.q = true;
- }
- } else {
- if (piece_color(move->piece) == WHITE) {
- if (move->fromrank == rankidx('1')) {
- if (move->fromfile == fileidx('e')) {
- gamestate->castling.K = gamestate->castling.Q = true;
- } else if (move->fromfile == fileidx('h')) {
- gamestate->castling.K = true;
- } else if (move->fromfile == fileidx('a')) {
- gamestate->castling.Q = true;
- }
- }
- } else {
- if (move->fromrank == rankidx('8')) {
- if (move->fromfile == fileidx('e')) {
- gamestate->castling.k = gamestate->castling.q = true;
- } else if (move->fromfile == fileidx('h')) {
- gamestate->castling.k = true;
- } else if (move->fromfile == fileidx('a')) {
- gamestate->castling.q = true;
- }
- }
- }
- }
-
- /* add move to the moves array and the new position to the FEN array */
- if (gamestate->movecount == gamestate->movecapacity) {
- gamestate->movecapacity += 64; /* 32 more full moves */
- gamestate->moves = realloc(gamestate->moves,
- gamestate->movecapacity * sizeof(Move));
- gamestate->fen = realloc(gamestate->fen,
- gamestate->movecapacity * sizeof(char*));
- }
-
- /* copy the move data into the game's move array */
- Move *melem = &gamestate->moves[gamestate->movecount];
- *melem = *move;
- calc_movetime(gamestate, melem);
-
- /* important: only "add" the move after calculating the time! */
- gamestate->movecount++;
-
- /* calculate the FEN of the new position and store it in the FEN array */
- char fen[FEN_MAX_LENGTH];
- fen_compute(fen, gamestate);
- gamestate->fen[gamestate->movecount - 1] = strdup(fen);
-}
-
void apply_move(GameState *gamestate, Move *move) {
apply_move_internal(gamestate, move);
@@ -440,132 +577,6 @@
}
}
-/* return 0 = no check, 1 = check, 2 = checkmate */
-static int determine_check_or_checkmate(
- const GameState *gamestate, const Move *move) {
-
- /* simulate the move */
- GameState simulation = gamestate_copy_sim(gamestate);
- Move simmove = *move;
- apply_move_internal(&simulation, &simmove);
-
- /* find the opposing king */
- Color piececolor = piece_color(move->piece);
- Color oppcolor = opponent_color(piececolor);
- File opkingfile = 0;
- Rank opkingrank = 0;
- for (Rank rank = 0 ; rank < 8 ; rank++) {
- for (File file = 0 ; file < 8 ; file++) {
- Piece p = piece_at(&simulation, file, rank);
- if (p == mkpiece(KING, oppcolor)) {
- opkingfile = file;
- opkingrank = rank;
- }
- }
- }
-
- /* determine if the opposing king is now threatened */
- Move threats[16];
- size_t threatcount;
- bool incheck = get_threats(&simulation, opkingfile, opkingrank,
- piececolor, threats, &threatcount);
-
- if (!incheck) {
- gamestate_cleanup(&simulation);
- return 0;
- }
-
- /* determine possible escape fields */
- bool canescape = false;
- for (int dr = -1 ; dr <= 1 && !canescape ; dr++) {
- for (int df = -1 ; df <= 1 && !canescape ; df++) {
- if (dr == 0 && df == 0) continue;
- Rank er = opkingrank + dr;
- File ef = opkingfile + df;
- if (!isidx(er) || !isidx(ef)) continue;
-
- /* check if piece of the king's color blocks the field */
- if (piece_color(simulation.board[er][ef]) == oppcolor)
- continue;
-
- /* check if escape field is already covered (threatened) */
- if (is_covered(&simulation, ef, er, piececolor))
- continue;
-
- /* check if an attacking piece blocks the field */
- if (piece_color(simulation.board[er][ef]) == piececolor) {
- /* test if the king can fight back */
- GameState sim_retaliate = gamestate_copy_sim(&simulation);
- Move move_retaliate = {0};
- move_retaliate.piece = mkpiece(KING, oppcolor);
- move_retaliate.fromrank = opkingrank;
- move_retaliate.fromfile = opkingfile;
- move_retaliate.torank = er;
- move_retaliate.tofile = ef;
- move_retaliate.capture = true;
- apply_move_internal(&sim_retaliate, &move_retaliate);
- canescape = !is_covered(&sim_retaliate, ef, er, piececolor);
- gamestate_cleanup(&sim_retaliate);
- continue;
- }
-
- /* the field is not covered and unoccupied */
- canescape = true;
- }
- }
-
- /* can't escape, can the king be rescued? */
- if (!canescape && threatcount == 1) {
- canescape = is_protected(&simulation,
- threats[0].fromfile, threats[0].fromrank, oppcolor);
- }
-
- /* can't capture, can he block? */
- if (!canescape && threatcount == 1) {
- Move *threat = &(threats[0]);
- unsigned tptype = piece_type(threat->piece);
-
- /* knight, pawns and the king cannot be blocked */
- if (tptype == BISHOP || tptype == ROOK || tptype == QUEEN) {
- if (threat->fromrank == threat->torank) {
- /* rook aspect (on rank) */
- int d = threat->tofile > threat->fromfile ? 1 : -1;
- File file = threat->fromfile;
- while (!canescape && file != threat->tofile - d) {
- file += d;
- canescape |= is_protected(&simulation,
- file, threat->torank, oppcolor);
- }
- } else if (threat->fromfile == threat->tofile) {
- /* rook aspect (on file) */
- int d = threat->torank > threat->fromrank ? 1 : -1;
- Rank rank = threat->fromrank;
- while (!canescape && rank != threat->torank - d) {
- rank += d;
- canescape |= is_protected(&simulation,
- threat->tofile, rank, oppcolor);
- }
- } else {
- /* bishop aspect */
- int dr = threat->torank > threat->fromrank ? 1 : -1;
- int df = threat->tofile > threat->fromfile ? 1 : -1;
-
- Rank rank = threat->fromrank;
- File file = threat->fromfile;
- while (!canescape && file != threat->tofile - df
- && rank != threat->torank - dr) {
- rank += dr;
- file += df;
- canescape |= is_protected(&simulation,
- file, rank, oppcolor);
- }
- }
- }
- }
- gamestate_cleanup(&simulation);
- return canescape ? 1 : 2;
-}
-
void format_move(const GameState *gamestate, Move *move) {
char *string = &(move->string[0]);