Rewrite do_castle_move()

And handle the castle directly in do/undo_move().
This allow to greatly simplify the code.

Here the beast is the nasty Chess960 that is
really tricky to get it right because could be
that 'from' and 'to' squares are the same or
that king's 'to' square is rook's 'from' square.

Anyhow should work: verified on all Chess960
starting positions.

No functional and no speed change also in Chess960.

diff --git a/src/position.cpp b/src/position.cpp
index 2cdcb4aecca934f237adec65f63dc628d85f2908..4045a25d96f454182b9de283b593d0b0d48c53c1 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -740,13 +740,6 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   st->rule50++;
   st->pliesFromNull++;
 
-  if (type_of(m) == CASTLE)
-  {
-      st->key = k;
-      do_castle_move<true>(m);
-      return;
-  }
-
   Color us = sideToMove;
   Color them = ~us;
   Square from = from_sq(m);
@@ -756,9 +749,25 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   PieceType capture = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
 
   assert(color_of(piece) == us);
-  assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them);
+  assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLE);
   assert(capture != KING);
 
+  if (type_of(m) == CASTLE)
+  {
+      assert(piece == make_piece(us, KING));
+
+      bool kingSide = to > from;
+      Square rfrom = to; // Castle is encoded as "king captures friendly rook"
+      Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
+      to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
+      capture = NO_PIECE_TYPE;
+
+      do_castle(from, to, rfrom, rto);
+
+      st->psqScore += psq_delta(make_piece(us, ROOK), rfrom, rto);
+      k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
+  }
+
   if (capture)
   {
       Square capsq = to;
@@ -835,19 +844,22 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
   // Prefetch TT access as soon as we know the new hash key
   prefetch((char*)TT.first_entry(k));
 
-  // Move the piece
-  Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
-  byTypeBB[ALL_PIECES] ^= from_to_bb;
-  byTypeBB[pt] ^= from_to_bb;
-  byColorBB[us] ^= from_to_bb;
-
-  board[to] = board[from];
-  board[from] = NO_PIECE;
-
-  // Update piece lists, index[from] is not updated and becomes stale. This
-  // works as long as index[] is accessed just by known occupied squares.
-  index[to] = index[from];
-  pieceList[us][pt][index[to]] = to;
+  // Move the piece. The tricky Chess960 castle is handled earlier
+  if (type_of(m) != CASTLE)
+  {
+      Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
+      byTypeBB[ALL_PIECES] ^= from_to_bb;
+      byTypeBB[pt] ^= from_to_bb;
+      byColorBB[us] ^= from_to_bb;
+
+      board[from] = NO_PIECE;
+      board[to] = piece;
+
+      // Update piece lists, index[from] is not updated and becomes stale. This
+      // works as long as index[] is accessed just by known occupied squares.
+      index[to] = index[from];
+      pieceList[us][pt][index[to]] = to;
+  }
 
   // If the moving piece is a pawn do some special extra work
   if (pt == PAWN)
@@ -952,19 +964,14 @@ void Position::undo_move(Move m) {
 
   sideToMove = ~sideToMove;
 
-  if (type_of(m) == CASTLE)
-      return do_castle_move<false>(m);
-
   Color us = sideToMove;
   Color them = ~us;
   Square from = from_sq(m);
   Square to = to_sq(m);
-  Piece piece = piece_on(to);
-  PieceType pt = type_of(piece);
+  PieceType pt = type_of(piece_on(to));
   PieceType capture = st->capturedType;
 
-  assert(is_empty(from));
-  assert(color_of(piece) == us);
+  assert(is_empty(from) || type_of(m) == CASTLE);
   assert(capture != KING);
 
   if (type_of(m) == PROMOTION)
@@ -992,19 +999,32 @@ void Position::undo_move(Move m) {
       pt = PAWN;
   }
 
-  // Put the piece back at the source square
-  Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
-  byTypeBB[ALL_PIECES] ^= from_to_bb;
-  byTypeBB[pt] ^= from_to_bb;
-  byColorBB[us] ^= from_to_bb;
-
-  board[from] = board[to];
-  board[to] = NO_PIECE;
-
-  // Update piece lists, index[to] is not updated and becomes stale. This
-  // works as long as index[] is accessed just by known occupied squares.
-  index[from] = index[to];
-  pieceList[us][pt][index[from]] = from;
+  if (type_of(m) == CASTLE)
+  {
+      bool kingSide = to > from;
+      Square rfrom = to; // Castle is encoded as "king captures friendly rook"
+      Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
+      to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
+      capture = NO_PIECE_TYPE;
+      pt = KING;
+      do_castle(to, from, rto, rfrom);
+  }
+  else
+  {
+      // Put the piece back at the source square
+      Bitboard from_to_bb = SquareBB[from] ^ SquareBB[to];
+      byTypeBB[ALL_PIECES] ^= from_to_bb;
+      byTypeBB[pt] ^= from_to_bb;
+      byColorBB[us] ^= from_to_bb;
+
+      board[to] = NO_PIECE;
+      board[from] = make_piece(us, pt);
+
+      // Update piece lists, index[to] is not updated and becomes stale. This
+      // works as long as index[] is accessed just by known occupied squares.
+      index[from] = index[to];
+      pieceList[us][pt][index[from]] = from;
+  }
 
   if (capture)
   {
@@ -1039,38 +1059,12 @@ void Position::undo_move(Move m) {
 }
 
 
-/// Position::do_castle_move() is a private method used to do/undo a castling
-/// move. Note that castling moves are encoded as "king captures friendly rook"
-/// moves, for instance white short castling in a non-Chess960 game is encoded
-/// as e1h1.
-template<bool Do>
-void Position::do_castle_move(Move m) {
+/// Position::do_castle() is a helper used to do/undo a castling move. This
+/// is a bit tricky, especially in Chess960.
 
-  assert(is_ok(m));
-  assert(type_of(m) == CASTLE);
+void Position::do_castle(Square kfrom, Square kto, Square rfrom, Square rto) {
 
   Color us = sideToMove;
-  Square kfrom, kto, rfrom, rto;
-
-  bool kingSide = to_sq(m) > from_sq(m);
-  kfrom = kto = from_sq(m);
-  rfrom = rto = to_sq(m);
-
-  if (Do)
-  {
-      kto = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
-      rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
-  }
-  else
-  {
-      kfrom = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
-      rfrom = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
-  }
-
-  assert(piece_on(kfrom) == make_piece(us, KING));
-  assert(piece_on(rfrom) == make_piece(us, ROOK));
-
-  // Move the pieces, with some care; in chess960 could be kto == rfrom
   Bitboard k_from_to_bb = SquareBB[kfrom] ^ SquareBB[kto];
   Bitboard r_from_to_bb = SquareBB[rfrom] ^ SquareBB[rto];
   byTypeBB[KING] ^= k_from_to_bb;
@@ -1078,52 +1072,17 @@ void Position::do_castle_move(Move m) {
   byTypeBB[ALL_PIECES] ^= k_from_to_bb ^ r_from_to_bb;
   byColorBB[us] ^= k_from_to_bb ^ r_from_to_bb;
 
-  // Update board
+  // Could be from == to, so first set NO_PIECE then KING and ROOK
   board[kfrom] = board[rfrom] = NO_PIECE;
   board[kto] = make_piece(us, KING);
   board[rto] = make_piece(us, ROOK);
 
-  // Update piece lists
-  pieceList[us][KING][index[kfrom]] = kto;
-  pieceList[us][ROOK][index[rfrom]] = rto;
-  int tmp = index[rfrom]; // In Chess960 could be kto == rfrom
-  index[kto] = index[kfrom];
-  index[rto] = tmp;
-
-  if (Do)
-  {
-      // Reset capture field
-      st->capturedType = NO_PIECE_TYPE;
-
-      // Update incremental scores
-      st->psqScore += psq_delta(make_piece(us, KING), kfrom, kto);
-      st->psqScore += psq_delta(make_piece(us, ROOK), rfrom, rto);
-
-      // Update hash key
-      st->key ^= Zobrist::psq[us][KING][kfrom] ^ Zobrist::psq[us][KING][kto];
-      st->key ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
-
-      // Clear en passant square
-      if (st->epSquare != SQ_NONE)
-      {
-          st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
-          st->epSquare = SQ_NONE;
-      }
-
-      // Update castling rights
-      st->key ^= Zobrist::castle[st->castleRights & castleRightsMask[kfrom]];
-      st->castleRights &= ~castleRightsMask[kfrom];
-
-      // Update checkers BB
-      st->checkersBB = attackers_to(king_square(~us)) & pieces(us);
-
-      sideToMove = ~sideToMove;
-  }
-  else
-      // Undo: point our state pointer back to the previous state
-      st = st->previous;
-
-  assert(pos_is_ok());
+  // Could be kfrom == rto, so use a 'tmp' variable
+  int tmp = index[kfrom];
+  index[rto] = index[rfrom];
+  index[kto] = tmp;
+  pieceList[us][KING][index[kto]] = kto;
+  pieceList[us][ROOK][index[rto]] = rto;
 }
 
 

diff --git a/src/position.h b/src/position.h
index 235cc8259ff05f83f3d035777453dacd9c04b325..8b475dd9f6f36a4e85ad6c925afdf7aadeec3e91 100644 (file)
--- a/src/position.h
+++ b/src/position.h
@@ -191,8 +191,8 @@ private:
   void put_piece(Piece p, Square s);
   void set_castle_right(Color c, Square rfrom);
 
-  // Helper template functions
-  template<bool Do> void do_castle_move(Move m);
+  // Helper functions
+  void do_castle(Square kfrom, Square kto, Square rfrom, Square rto);
   template<bool FindPinned> Bitboard hidden_checkers() const;
 
   // Computing hash keys from scratch (for initialization and debugging)