Introduce StateInfo instead of UndoInfo

We don't backup anymore but use the renamed StateInfo
argument passed in do_move() to store the new position
state when doing a move.

Backup is now just revert to previous StateInfo that we know
because we store a pointer to it.
Note that now backing store is up to the caller, Position is
stateless in that regard, state is accessed through a pointer.

This patch will let us remove all the backup/restore copying,
just a pointer switch is now necessary.

Note that do_null_move() still uses StateInfo as backup.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/position.cpp b/src/position.cpp
index 76ebbde42e6d962b831e18dec60d02f43817d444..e2eeda85ac1e3c5d1f12728d530a840d1039b1a6 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -192,7 +192,7 @@ void Position::from_fen(const std::string& fen) {
   if (    i < fen.length() - 2
       && (fen[i] >= 'a' && fen[i] <= 'h')
       && (fen[i+1] == '3' || fen[i+1] == '6'))
   if (    i < fen.length() - 2
       && (fen[i] >= 'a' && fen[i] <= 'h')
       && (fen[i+1] == '3' || fen[i+1] == '6'))

-      st.epSquare = square_from_string(fen.substr(i, 2));
+      st->epSquare = square_from_string(fen.substr(i, 2));

 
   // Various initialisation
   for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
 
   // Various initialisation
   for (Square sq = SQ_A1; sq <= SQ_H8; sq++)


@@ -207,11 +207,11 @@ void Position::from_fen(const std::string& fen) {
 
   find_checkers();
 
 
   find_checkers();
 

-  st.key = compute_key();
-  st.pawnKey = compute_pawn_key();
-  st.materialKey = compute_material_key();
-  st.mgValue = compute_value<MidGame>();
-  st.egValue = compute_value<EndGame>();
+  st->key = compute_key();
+  st->pawnKey = compute_pawn_key();
+  st->materialKey = compute_material_key();
+  st->mgValue = compute_value<MidGame>();
+  st->egValue = compute_value<EndGame>();

   npMaterial[WHITE] = compute_non_pawn_material(WHITE);
   npMaterial[BLACK] = compute_non_pawn_material(BLACK);
 }
   npMaterial[WHITE] = compute_non_pawn_material(WHITE);
   npMaterial[BLACK] = compute_non_pawn_material(BLACK);
 }


@@ -249,7 +249,7 @@ const std::string Position::to_fen() const {
       fen += (rank > RANK_1 ? '/' : ' ');
   }
   fen += (sideToMove == WHITE ? "w " : "b ");
       fen += (rank > RANK_1 ? '/' : ' ');
   }
   fen += (sideToMove == WHITE ? "w " : "b ");

-  if (st.castleRights != NO_CASTLES)
+  if (st->castleRights != NO_CASTLES)

   {
     if (can_castle_kingside(WHITE))  fen += 'K';
     if (can_castle_queenside(WHITE)) fen += 'Q';
   {
     if (can_castle_kingside(WHITE))  fen += 'K';
     if (can_castle_queenside(WHITE)) fen += 'Q';


@@ -305,7 +305,7 @@ void Position::print(Move m) const {
   }
   std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
             << "Fen is: " << to_fen() << std::endl
   }
   std::cout << "+---+---+---+---+---+---+---+---+" << std::endl
             << "Fen is: " << to_fen() << std::endl

-            << "Key is: " << st.key << std::endl;
+            << "Key is: " << st->key << std::endl;

 
   RequestPending = false;
 }
 
   RequestPending = false;
 }


@@ -323,34 +323,34 @@ void Position::copy(const Position &pos) {
 /// king) pieces for the given color.
 Bitboard Position::pinned_pieces(Color c) const {
 
 /// king) pieces for the given color.
 Bitboard Position::pinned_pieces(Color c) const {
 

-  if (st.pinned[c] != ~EmptyBoardBB)
-      return st.pinned[c];
+  if (st->pinned[c] != ~EmptyBoardBB)
+      return st->pinned[c];

 
   Bitboard p1, p2;
   Square ksq = king_square(c);
 
   Bitboard p1, p2;
   Square ksq = king_square(c);

-  st.pinned[c] = hidden_checks<ROOK, true>(c, ksq, p1) | hidden_checks<BISHOP, true>(c, ksq, p2);
-  st.pinners[c] = p1 | p2;
-  return st.pinned[c];
+  st->pinned[c] = hidden_checks<ROOK, true>(c, ksq, p1) | hidden_checks<BISHOP, true>(c, ksq, p2);
+  st->pinners[c] = p1 | p2;
+  return st->pinned[c];

 }
 
 Bitboard Position::pinned_pieces(Color c, Bitboard& p) const {
 
 }
 
 Bitboard Position::pinned_pieces(Color c, Bitboard& p) const {
 

-  if (st.pinned[c] == ~EmptyBoardBB)
+  if (st->pinned[c] == ~EmptyBoardBB)

       pinned_pieces(c);
 
       pinned_pieces(c);
 

-  p = st.pinners[c];
-  return st.pinned[c];
+  p = st->pinners[c];
+  return st->pinned[c];

 }
 
 Bitboard Position::discovered_check_candidates(Color c) const {
 
 }
 
 Bitboard Position::discovered_check_candidates(Color c) const {
 

-  if (st.dcCandidates[c] != ~EmptyBoardBB)
-      return st.dcCandidates[c];
+  if (st->dcCandidates[c] != ~EmptyBoardBB)
+      return st->dcCandidates[c];

 
   Bitboard dummy;
   Square ksq = king_square(opposite_color(c));
 
   Bitboard dummy;
   Square ksq = king_square(opposite_color(c));

-  st.dcCandidates[c] = hidden_checks<ROOK, false>(c, ksq, dummy) | hidden_checks<BISHOP, false>(c, ksq, dummy);
-  return st.dcCandidates[c];
+  st->dcCandidates[c] = hidden_checks<ROOK, false>(c, ksq, dummy) | hidden_checks<BISHOP, false>(c, ksq, dummy);
+  return st->dcCandidates[c];

 }
 
 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the
 }
 
 /// Position:hidden_checks<>() returns a bitboard of all pinned (against the


@@ -368,14 +368,14 @@ Bitboard Position::hidden_checks(Color c, Square ksq, Bitboard& pinners) const {
   else
       sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
 
   else
       sliders = bishops_and_queens(FindPinned ? opposite_color(c) : c) & BishopPseudoAttacks[ksq];
 

-  if (sliders && (!FindPinned || (sliders & ~st.checkersBB)))
+  if (sliders && (!FindPinned || (sliders & ~st->checkersBB)))

   {
        // King blockers are candidate pinned pieces
       Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
 
       // Pinners are sliders, not checkers, that give check when
       // candidate pinned are removed.
   {
        // King blockers are candidate pinned pieces
       Bitboard candidate_pinned = piece_attacks<Piece>(ksq) & pieces_of_color(c);
 
       // Pinners are sliders, not checkers, that give check when
       // candidate pinned are removed.

-      pinners = (FindPinned ? sliders & ~st.checkersBB : sliders);
+      pinners = (FindPinned ? sliders & ~st->checkersBB : sliders);

 
       if (Piece == ROOK)
           pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);
 
       if (Piece == ROOK)
           pinners &= rook_attacks_bb(ksq, occupied_squares() ^ candidate_pinned);


@@ -474,7 +474,7 @@ bool Position::move_attacks_square(Move m, Square s) const {
 void Position::find_checkers() {
 
   Color us = side_to_move();
 void Position::find_checkers() {
 
   Color us = side_to_move();

-  st.checkersBB = attacks_to(king_square(us), opposite_color(us));
+  st->checkersBB = attacks_to(king_square(us), opposite_color(us));

 }
 
 
 }
 
 


@@ -689,11 +689,11 @@ inline void Position::update_checkers(Bitboard* pCheckersBB, Square ksq, Square
 }
 
 
 }
 
 

-/// Position::do_move() makes a move, and backs up all information necessary
-/// to undo the move to an UndoInfo object. The move is assumed to be legal.
+/// Position::do_move() makes a move, and saves all information necessary
+/// to a StateInfo object. The move is assumed to be legal.

 /// Pseudo-legal moves should be filtered out before this function is called.
 
 /// Pseudo-legal moves should be filtered out before this function is called.
 

-void Position::do_move(Move m, UndoInfo& u) {
+void Position::do_move(Move m, StateInfo& newSt) {

 
   assert(is_ok());
   assert(move_is_ok(m));
 
   assert(is_ok());
   assert(move_is_ok(m));


@@ -702,23 +702,26 @@ void Position::do_move(Move m, UndoInfo& u) {
   // in update_checkers().
   Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
 
   // in update_checkers().
   Bitboard oldDcCandidates = discovered_check_candidates(side_to_move());
 

-  // Back up the necessary information to our UndoInfo object (except the
+  // Copy the old state to our new StateInfo object (except the

   // captured piece, which is taken care of later.
   // captured piece, which is taken care of later.

-  u = undoInfoUnion;
-  u.capture = NO_PIECE_TYPE;
-  st.previous = &u;
+  // TODO do not copy pinners and checkersBB because are recalculated
+  // anyway.
+  newSt = *st;
+  newSt.capture = NO_PIECE_TYPE;
+  newSt.previous = st;
+  st = &newSt;

 
   // Save the current key to the history[] array, in order to be able to
   // detect repetition draws.
 
   // Save the current key to the history[] array, in order to be able to
   // detect repetition draws.

-  history[gamePly] = st.key;
+  history[gamePly] = st->key;

 
   // Increment the 50 moves rule draw counter. Resetting it to zero in the
   // case of non-reversible moves is taken care of later.
 
   // Increment the 50 moves rule draw counter. Resetting it to zero in the
   // case of non-reversible moves is taken care of later.

-  st.rule50++;
+  st->rule50++;

 
   // Reset pinned bitboard and its friends
   for (Color c = WHITE; c <= BLACK; c++)
 
   // Reset pinned bitboard and its friends
   for (Color c = WHITE; c <= BLACK; c++)

-      st.pinners[c] = st.pinned[c] = st.dcCandidates[c] = ~EmptyBoardBB;
+      st->pinners[c] = st->pinned[c] = st->dcCandidates[c] = ~EmptyBoardBB;

 
   if (move_is_castle(m))
       do_castle_move(m);
 
   if (move_is_castle(m))
       do_castle_move(m);


@@ -738,13 +741,10 @@ void Position::do_move(Move m, UndoInfo& u) {
 
     PieceType piece = type_of_piece_on(from);
 
 
     PieceType piece = type_of_piece_on(from);
 

-    st.capture = type_of_piece_on(to);
+    st->capture = type_of_piece_on(to);

 
 

-    if (st.capture)
-    {
-      u.capture = st.capture;
-      do_capture_move(m, st.capture, them, to);
-    }
+    if (st->capture)
+      do_capture_move(m, st->capture, them, to);

 
     // Move the piece
     clear_bit(&(byColorBB[us]), from);
 
     // Move the piece
     clear_bit(&(byColorBB[us]), from);


@@ -757,33 +757,33 @@ void Position::do_move(Move m, UndoInfo& u) {
     board[from] = EMPTY;
 
     // Update hash key
     board[from] = EMPTY;
 
     // Update hash key

-    st.key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
+    st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];

 
     // Update incremental scores
 
     // Update incremental scores

-    st.mgValue -= pst<MidGame>(us, piece, from);
-    st.mgValue += pst<MidGame>(us, piece, to);
-    st.egValue -= pst<EndGame>(us, piece, from);
-    st.egValue += pst<EndGame>(us, piece, to);
+    st->mgValue -= pst<MidGame>(us, piece, from);
+    st->mgValue += pst<MidGame>(us, piece, to);
+    st->egValue -= pst<EndGame>(us, piece, from);
+    st->egValue += pst<EndGame>(us, piece, to);

 
     // If the moving piece was a king, update the king square
     if (piece == KING)
         kingSquare[us] = to;
 
     // Reset en passant square
 
     // If the moving piece was a king, update the king square
     if (piece == KING)
         kingSquare[us] = to;
 
     // Reset en passant square

-    if (st.epSquare != SQ_NONE)
+    if (st->epSquare != SQ_NONE)

     {
     {

-        st.key ^= zobEp[st.epSquare];
-        st.epSquare = SQ_NONE;
+        st->key ^= zobEp[st->epSquare];
+        st->epSquare = SQ_NONE;

     }
 
     // If the moving piece was a pawn do some special extra work
     if (piece == PAWN)
     {
         // Reset rule 50 draw counter
     }
 
     // If the moving piece was a pawn do some special extra work
     if (piece == PAWN)
     {
         // Reset rule 50 draw counter

-        st.rule50 = 0;
+        st->rule50 = 0;

 
         // Update pawn hash key
 
         // Update pawn hash key

-        st.pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
+        st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];

 
         // Set en passant square, only if moved pawn can be captured
         if (abs(int(to) - int(from)) == 16)
 
         // Set en passant square, only if moved pawn can be captured
         if (abs(int(to) - int(from)) == 16)


@@ -791,8 +791,8 @@ void Position::do_move(Move m, UndoInfo& u) {
             if (   (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
                 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
             {
             if (   (us == WHITE && (pawn_attacks(WHITE, from + DELTA_N) & pawns(BLACK)))
                 || (us == BLACK && (pawn_attacks(BLACK, from + DELTA_S) & pawns(WHITE))))
             {

-                st.epSquare = Square((int(from) + int(to)) / 2);
-                st.key ^= zobEp[st.epSquare];
+                st->epSquare = Square((int(from) + int(to)) / 2);
+                st->key ^= zobEp[st->epSquare];

             }
         }
     }
             }
         }
     }


@@ -802,33 +802,33 @@ void Position::do_move(Move m, UndoInfo& u) {
     index[to] = index[from];
 
     // Update castle rights
     index[to] = index[from];
 
     // Update castle rights

-    st.key ^= zobCastle[st.castleRights];
-    st.castleRights &= castleRightsMask[from];
-    st.castleRights &= castleRightsMask[to];
-    st.key ^= zobCastle[st.castleRights];
+    st->key ^= zobCastle[st->castleRights];
+    st->castleRights &= castleRightsMask[from];
+    st->castleRights &= castleRightsMask[to];
+    st->key ^= zobCastle[st->castleRights];

 
     // Update checkers bitboard, piece must be already moved
 
     // Update checkers bitboard, piece must be already moved

-    st.checkersBB = EmptyBoardBB;
+    st->checkersBB = EmptyBoardBB;

     Square ksq = king_square(them);
     switch (piece)
     {
     Square ksq = king_square(them);
     switch (piece)
     {

-    case PAWN:   update_checkers<PAWN>(&st.checkersBB, ksq, from, to, oldDcCandidates);   break;
-    case KNIGHT: update_checkers<KNIGHT>(&st.checkersBB, ksq, from, to, oldDcCandidates); break;
-    case BISHOP: update_checkers<BISHOP>(&st.checkersBB, ksq, from, to, oldDcCandidates); break;
-    case ROOK:   update_checkers<ROOK>(&st.checkersBB, ksq, from, to, oldDcCandidates);   break;
-    case QUEEN:  update_checkers<QUEEN>(&st.checkersBB, ksq, from, to, oldDcCandidates);  break;
-    case KING:   update_checkers<KING>(&st.checkersBB, ksq, from, to, oldDcCandidates);   break;
+    case PAWN:   update_checkers<PAWN>(&st->checkersBB, ksq, from, to, oldDcCandidates);   break;
+    case KNIGHT: update_checkers<KNIGHT>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
+    case BISHOP: update_checkers<BISHOP>(&st->checkersBB, ksq, from, to, oldDcCandidates); break;
+    case ROOK:   update_checkers<ROOK>(&st->checkersBB, ksq, from, to, oldDcCandidates);   break;
+    case QUEEN:  update_checkers<QUEEN>(&st->checkersBB, ksq, from, to, oldDcCandidates);  break;
+    case KING:   update_checkers<KING>(&st->checkersBB, ksq, from, to, oldDcCandidates);   break;

     default: assert(false); break;
     }
   }
 
   // Finish
     default: assert(false); break;
     }
   }
 
   // Finish

-  st.key ^= zobSideToMove;
+  st->key ^= zobSideToMove;

   sideToMove = opposite_color(sideToMove);
   gamePly++;
 
   sideToMove = opposite_color(sideToMove);
   gamePly++;
 

-  st.mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
-  st.egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
+  st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
+  st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;

 
   assert(is_ok());
 }
 
   assert(is_ok());
 }


@@ -846,15 +846,15 @@ void Position::do_capture_move(Move m, PieceType capture, Color them, Square to)
     clear_bit(&(byTypeBB[capture]), to);
 
     // Update hash key
     clear_bit(&(byTypeBB[capture]), to);
 
     // Update hash key

-    st.key ^= zobrist[them][capture][to];
+    st->key ^= zobrist[them][capture][to];

 
     // If the captured piece was a pawn, update pawn hash key
     if (capture == PAWN)
 
     // If the captured piece was a pawn, update pawn hash key
     if (capture == PAWN)

-        st.pawnKey ^= zobrist[them][PAWN][to];
+        st->pawnKey ^= zobrist[them][PAWN][to];

 
     // Update incremental scores
 
     // Update incremental scores

-    st.mgValue -= pst<MidGame>(them, capture, to);
-    st.egValue -= pst<EndGame>(them, capture, to);
+    st->mgValue -= pst<MidGame>(them, capture, to);
+    st->egValue -= pst<EndGame>(them, capture, to);

 
     assert(!move_promotion(m) || capture != PAWN);
 
 
     assert(!move_promotion(m) || capture != PAWN);
 


@@ -863,7 +863,7 @@ void Position::do_capture_move(Move m, PieceType capture, Color them, Square to)
         npMaterial[them] -= piece_value_midgame(capture);
 
     // Update material hash key
         npMaterial[them] -= piece_value_midgame(capture);
 
     // Update material hash key

-    st.materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];
+    st->materialKey ^= zobMaterial[them][capture][pieceCount[them][capture]];

 
     // Update piece count
     pieceCount[them][capture]--;
 
     // Update piece count
     pieceCount[them][capture]--;


@@ -873,7 +873,7 @@ void Position::do_capture_move(Move m, PieceType capture, Color them, Square to)
     index[pieceList[them][capture][index[to]]] = index[to];
 
     // Reset rule 50 counter
     index[pieceList[them][capture][index[to]]] = index[to];
 
     // Reset rule 50 counter

-    st.rule50 = 0;
+    st->rule50 = 0;

 }
 
 
 }
 
 


@@ -941,43 +941,41 @@ void Position::do_castle_move(Move m) {
   index[rto] = tmp;
 
   // Update incremental scores
   index[rto] = tmp;
 
   // Update incremental scores

-  st.mgValue -= pst<MidGame>(us, KING, kfrom);
-  st.mgValue += pst<MidGame>(us, KING, kto);
-  st.egValue -= pst<EndGame>(us, KING, kfrom);
-  st.egValue += pst<EndGame>(us, KING, kto);
-  st.mgValue -= pst<MidGame>(us, ROOK, rfrom);
-  st.mgValue += pst<MidGame>(us, ROOK, rto);
-  st.egValue -= pst<EndGame>(us, ROOK, rfrom);
-  st.egValue += pst<EndGame>(us, ROOK, rto);
+  st->mgValue -= pst<MidGame>(us, KING, kfrom);
+  st->mgValue += pst<MidGame>(us, KING, kto);
+  st->egValue -= pst<EndGame>(us, KING, kfrom);
+  st->egValue += pst<EndGame>(us, KING, kto);
+  st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
+  st->mgValue += pst<MidGame>(us, ROOK, rto);
+  st->egValue -= pst<EndGame>(us, ROOK, rfrom);
+  st->egValue += pst<EndGame>(us, ROOK, rto);

 
   // Update hash key
 
   // Update hash key

-  st.key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
-  st.key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
+  st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
+  st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];

 
   // Clear en passant square
 
   // Clear en passant square

-  if (st.epSquare != SQ_NONE)
+  if (st->epSquare != SQ_NONE)

   {
   {

-      st.key ^= zobEp[st.epSquare];
-      st.epSquare = SQ_NONE;
+      st->key ^= zobEp[st->epSquare];
+      st->epSquare = SQ_NONE;

   }
 
   // Update castling rights
   }
 
   // Update castling rights

-  st.key ^= zobCastle[st.castleRights];
-  st.castleRights &= castleRightsMask[kfrom];
-  st.key ^= zobCastle[st.castleRights];
+  st->key ^= zobCastle[st->castleRights];
+  st->castleRights &= castleRightsMask[kfrom];
+  st->key ^= zobCastle[st->castleRights];

 
   // Reset rule 50 counter
 
   // Reset rule 50 counter

-  st.rule50 = 0;
+  st->rule50 = 0;

 
   // Update checkers BB
 
   // Update checkers BB

-  st.checkersBB = attacks_to(king_square(them), us);
+  st->checkersBB = attacks_to(king_square(them), us);

 }
 
 
 /// Position::do_promotion_move() is a private method used to make a promotion
 }
 
 
 /// Position::do_promotion_move() is a private method used to make a promotion

-/// move. It is called from the main Position::do_move function. The
-/// UndoInfo object, which has been initialized in Position::do_move, is
-/// used to store the captured piece (if any).
+/// move. It is called from the main Position::do_move function.

 
 void Position::do_promotion_move(Move m) {
 
 
 void Position::do_promotion_move(Move m) {
 


@@ -998,13 +996,10 @@ void Position::do_promotion_move(Move m) {
   assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
   assert(color_of_piece_on(to) == them || square_is_empty(to));
 
   assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
   assert(color_of_piece_on(to) == them || square_is_empty(to));
 

-  st.capture = type_of_piece_on(to);
+  st->capture = type_of_piece_on(to);

 
 

-  if (st.capture)
-  {
-    st.previous->capture = st.capture;
-    do_capture_move(m, st.capture, them, to);
-  }
+  if (st->capture)
+    do_capture_move(m, st->capture, them, to);

 
   // Remove pawn
   clear_bit(&(byColorBB[us]), from);
 
   // Remove pawn
   clear_bit(&(byColorBB[us]), from);


@@ -1021,14 +1016,14 @@ void Position::do_promotion_move(Move m) {
   board[to] = piece_of_color_and_type(us, promotion);
 
   // Update hash key
   board[to] = piece_of_color_and_type(us, promotion);
 
   // Update hash key

-  st.key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];
+  st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][promotion][to];

 
   // Update pawn hash key
 
   // Update pawn hash key

-  st.pawnKey ^= zobrist[us][PAWN][from];
+  st->pawnKey ^= zobrist[us][PAWN][from];

 
   // Update material key
 
   // Update material key

-  st.materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
-  st.materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];
+  st->materialKey ^= zobMaterial[us][PAWN][pieceCount[us][PAWN]];
+  st->materialKey ^= zobMaterial[us][promotion][pieceCount[us][promotion]+1];

 
   // Update piece counts
   pieceCount[us][PAWN]--;
 
   // Update piece counts
   pieceCount[us][PAWN]--;


@@ -1041,38 +1036,36 @@ void Position::do_promotion_move(Move m) {
   index[to] = pieceCount[us][promotion] - 1;
 
   // Update incremental scores
   index[to] = pieceCount[us][promotion] - 1;
 
   // Update incremental scores

-  st.mgValue -= pst<MidGame>(us, PAWN, from);
-  st.mgValue += pst<MidGame>(us, promotion, to);
-  st.egValue -= pst<EndGame>(us, PAWN, from);
-  st.egValue += pst<EndGame>(us, promotion, to);
+  st->mgValue -= pst<MidGame>(us, PAWN, from);
+  st->mgValue += pst<MidGame>(us, promotion, to);
+  st->egValue -= pst<EndGame>(us, PAWN, from);
+  st->egValue += pst<EndGame>(us, promotion, to);

 
   // Update material
   npMaterial[us] += piece_value_midgame(promotion);
 
   // Clear the en passant square
 
   // Update material
   npMaterial[us] += piece_value_midgame(promotion);
 
   // Clear the en passant square

-  if (st.epSquare != SQ_NONE)
+  if (st->epSquare != SQ_NONE)

   {
   {

-      st.key ^= zobEp[st.epSquare];
-      st.epSquare = SQ_NONE;
+      st->key ^= zobEp[st->epSquare];
+      st->epSquare = SQ_NONE;

   }
 
   // Update castle rights
   }
 
   // Update castle rights

-  st.key ^= zobCastle[st.castleRights];
-  st.castleRights &= castleRightsMask[to];
-  st.key ^= zobCastle[st.castleRights];
+  st->key ^= zobCastle[st->castleRights];
+  st->castleRights &= castleRightsMask[to];
+  st->key ^= zobCastle[st->castleRights];

 
   // Reset rule 50 counter
 
   // Reset rule 50 counter

-  st.rule50 = 0;
+  st->rule50 = 0;

 
   // Update checkers BB
 
   // Update checkers BB

-  st.checkersBB = attacks_to(king_square(them), us);
+  st->checkersBB = attacks_to(king_square(them), us);

 }
 
 
 /// Position::do_ep_move() is a private method used to make an en passant
 }
 
 
 /// Position::do_ep_move() is a private method used to make an en passant

-/// capture. It is called from the main Position::do_move function. Because
-/// the captured piece is always a pawn, we don't need to pass an UndoInfo
-/// object in which to store the captured piece.
+/// capture. It is called from the main Position::do_move function.

 
 void Position::do_ep_move(Move m) {
 
 
 void Position::do_ep_move(Move m) {
 


@@ -1089,7 +1082,7 @@ void Position::do_ep_move(Move m) {
   to = move_to(m);
   capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
 
   to = move_to(m);
   capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
 

-  assert(to == st.epSquare);
+  assert(to == st->epSquare);

   assert(relative_rank(us, to) == RANK_6);
   assert(piece_on(to) == EMPTY);
   assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
   assert(relative_rank(us, to) == RANK_6);
   assert(piece_on(to) == EMPTY);
   assert(piece_on(from) == piece_of_color_and_type(us, PAWN));


@@ -1114,7 +1107,7 @@ void Position::do_ep_move(Move m) {
   board[from] = EMPTY;
 
   // Update material hash key
   board[from] = EMPTY;
 
   // Update material hash key

-  st.materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];
+  st->materialKey ^= zobMaterial[them][PAWN][pieceCount[them][PAWN]];

 
   // Update piece count
   pieceCount[them][PAWN]--;
 
   // Update piece count
   pieceCount[them][PAWN]--;


@@ -1126,37 +1119,35 @@ void Position::do_ep_move(Move m) {
   index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
 
   // Update hash key
   index[pieceList[them][PAWN][index[capsq]]] = index[capsq];
 
   // Update hash key

-  st.key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
-  st.key ^= zobrist[them][PAWN][capsq];
-  st.key ^= zobEp[st.epSquare];
+  st->key ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
+  st->key ^= zobrist[them][PAWN][capsq];
+  st->key ^= zobEp[st->epSquare];

 
   // Update pawn hash key
 
   // Update pawn hash key

-  st.pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
-  st.pawnKey ^= zobrist[them][PAWN][capsq];
+  st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
+  st->pawnKey ^= zobrist[them][PAWN][capsq];

 
   // Update incremental scores
 
   // Update incremental scores

-  st.mgValue -= pst<MidGame>(them, PAWN, capsq);
-  st.mgValue -= pst<MidGame>(us, PAWN, from);
-  st.mgValue += pst<MidGame>(us, PAWN, to);
-  st.egValue -= pst<EndGame>(them, PAWN, capsq);
-  st.egValue -= pst<EndGame>(us, PAWN, from);
-  st.egValue += pst<EndGame>(us, PAWN, to);
+  st->mgValue -= pst<MidGame>(them, PAWN, capsq);
+  st->mgValue -= pst<MidGame>(us, PAWN, from);
+  st->mgValue += pst<MidGame>(us, PAWN, to);
+  st->egValue -= pst<EndGame>(them, PAWN, capsq);
+  st->egValue -= pst<EndGame>(us, PAWN, from);
+  st->egValue += pst<EndGame>(us, PAWN, to);

 
   // Reset en passant square
 
   // Reset en passant square

-  st.epSquare = SQ_NONE;
+  st->epSquare = SQ_NONE;

 
   // Reset rule 50 counter
 
   // Reset rule 50 counter

-  st.rule50 = 0;
+  st->rule50 = 0;

 
   // Update checkers BB
 
   // Update checkers BB

-  st.checkersBB = attacks_to(king_square(them), us);
+  st->checkersBB = attacks_to(king_square(them), us);

 }
 
 
 /// Position::undo_move() unmakes a move. When it returns, the position should
 }
 
 
 /// Position::undo_move() unmakes a move. When it returns, the position should

-/// be restored to exactly the same state as before the move was made. It is
-/// important that Position::undo_move is called with the same move and UndoInfo
-/// object as the earlier call to Position::do_move.
+/// be restored to exactly the same state as before the move was made.

 
 void Position::undo_move(Move m) {
 
 
 void Position::undo_move(Move m) {
 


@@ -1166,10 +1157,6 @@ void Position::undo_move(Move m) {
   gamePly--;
   sideToMove = opposite_color(sideToMove);
 
   gamePly--;
   sideToMove = opposite_color(sideToMove);
 

-  // Restore information from our UndoInfo object (except the captured piece,
-  // which is taken care of later)
-  undoInfoUnion = *(st.previous);
-

   if (move_is_castle(m))
       undo_castle_move(m);
   else if (move_promotion(m))
   if (move_is_castle(m))
       undo_castle_move(m);
   else if (move_promotion(m))


@@ -1210,30 +1197,33 @@ void Position::undo_move(Move m) {
       pieceList[us][piece][index[to]] = from;
       index[from] = index[to];
 
       pieceList[us][piece][index[to]] = from;
       index[from] = index[to];
 

-      if (st.capture)
+      if (st->capture)

       {
           assert(capture != KING);
 
           // Replace the captured piece
           set_bit(&(byColorBB[them]), to);
       {
           assert(capture != KING);
 
           // Replace the captured piece
           set_bit(&(byColorBB[them]), to);

-          set_bit(&(byTypeBB[st.capture]), to);
+          set_bit(&(byTypeBB[st->capture]), to);

           set_bit(&(byTypeBB[0]), to);
           set_bit(&(byTypeBB[0]), to);

-          board[to] = piece_of_color_and_type(them, st.capture);
+          board[to] = piece_of_color_and_type(them, st->capture);

 
           // Update material
 
           // Update material

-          if (st.capture != PAWN)
-              npMaterial[them] += piece_value_midgame(st.capture);
+          if (st->capture != PAWN)
+              npMaterial[them] += piece_value_midgame(st->capture);

 
           // Update piece list
 
           // Update piece list

-          pieceList[them][st.capture][pieceCount[them][st.capture]] = to;
-          index[to] = pieceCount[them][st.capture];
+          pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
+          index[to] = pieceCount[them][st->capture];

 
           // Update piece count
 
           // Update piece count

-          pieceCount[them][st.capture]++;
+          pieceCount[them][st->capture]++;

       } else
           board[to] = EMPTY;
   }
 
       } else
           board[to] = EMPTY;
   }
 

+  // Finally point out state pointer back to the previous state
+  st = st->previous;
+

   assert(is_ok());
 }
 
   assert(is_ok());
 }
 


@@ -1306,8 +1296,7 @@ void Position::undo_castle_move(Move m) {
 
 /// Position::undo_promotion_move() is a private method used to unmake a
 /// promotion move. It is called from the main Position::do_move
 
 /// Position::undo_promotion_move() is a private method used to unmake a
 /// promotion move. It is called from the main Position::do_move

-/// function. The UndoInfo object, which has been initialized in
-/// Position::do_move, is used to put back the captured piece (if any).
+/// function.

 
 void Position::undo_promotion_move(Move m) {
 
 
 void Position::undo_promotion_move(Move m) {
 


@@ -1357,36 +1346,34 @@ void Position::undo_promotion_move(Move m) {
   pieceCount[us][promotion]--;
   pieceCount[us][PAWN]++;
 
   pieceCount[us][promotion]--;
   pieceCount[us][PAWN]++;
 

-  if (st.capture)
+  if (st->capture)

   {
       assert(capture != KING);
 
       // Insert captured piece:
       set_bit(&(byColorBB[them]), to);
   {
       assert(capture != KING);
 
       // Insert captured piece:
       set_bit(&(byColorBB[them]), to);

-      set_bit(&(byTypeBB[st.capture]), to);
+      set_bit(&(byTypeBB[st->capture]), to);

       set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares
       set_bit(&(byTypeBB[0]), to); // HACK: byTypeBB[0] == occupied squares

-      board[to] = piece_of_color_and_type(them, st.capture);
+      board[to] = piece_of_color_and_type(them, st->capture);

 
       // Update material. Because the move is a promotion move, we know
       // that the captured piece cannot be a pawn.
       assert(capture != PAWN);
 
       // Update material. Because the move is a promotion move, we know
       // that the captured piece cannot be a pawn.
       assert(capture != PAWN);

-      npMaterial[them] += piece_value_midgame(st.capture);
+      npMaterial[them] += piece_value_midgame(st->capture);

 
       // Update piece list
 
       // Update piece list

-      pieceList[them][st.capture][pieceCount[them][st.capture]] = to;
-      index[to] = pieceCount[them][st.capture];
+      pieceList[them][st->capture][pieceCount[them][st->capture]] = to;
+      index[to] = pieceCount[them][st->capture];

 
       // Update piece count
 
       // Update piece count

-      pieceCount[them][st.capture]++;
+      pieceCount[them][st->capture]++;

   } else
       board[to] = EMPTY;
 }
 
 
 /// Position::undo_ep_move() is a private method used to unmake an en passant
   } else
       board[to] = EMPTY;
 }
 
 
 /// Position::undo_ep_move() is a private method used to unmake an en passant

-/// capture. It is called from the main Position::undo_move function.  Because
-/// the captured piece is always a pawn, we don't need to pass an UndoInfo
-/// object from which to retrieve the captured piece.
+/// capture. It is called from the main Position::undo_move function.

 
 void Position::undo_ep_move(Move m) {
 
 
 void Position::undo_ep_move(Move m) {
 


@@ -1440,35 +1427,35 @@ void Position::undo_ep_move(Move m) {
 /// Position::do_null_move makes() a "null move": It switches the side to move
 /// and updates the hash key without executing any move on the board.
 
 /// Position::do_null_move makes() a "null move": It switches the side to move
 /// and updates the hash key without executing any move on the board.
 

-void Position::do_null_move(UndoInfo& u) {
+void Position::do_null_move(StateInfo& newSt) {

 
   assert(is_ok());
   assert(!is_check());
 
   // Back up the information necessary to undo the null move to the supplied
 
   assert(is_ok());
   assert(!is_check());
 
   // Back up the information necessary to undo the null move to the supplied

-  // UndoInfo object. In the case of a null move, the only thing we need to
+  // StateInfo object. In the case of a null move, the only thing we need to

   // remember is the last move made and the en passant square.
   // remember is the last move made and the en passant square.

-  u.lastMove = st.lastMove;
-  u.epSquare = st.epSquare;
-  u.previous = st.previous;
-  st.previous = &u;
+  newSt.lastMove = st->lastMove;
+  newSt.epSquare = st->epSquare;
+  newSt.previous = st->previous;
+  st->previous = &newSt;

 
   // Save the current key to the history[] array, in order to be able to
   // detect repetition draws.
 
   // Save the current key to the history[] array, in order to be able to
   // detect repetition draws.

-  history[gamePly] = st.key;
+  history[gamePly] = st->key;

 
   // Update the necessary information
   sideToMove = opposite_color(sideToMove);
 
   // Update the necessary information
   sideToMove = opposite_color(sideToMove);

-  if (st.epSquare != SQ_NONE)
-      st.key ^= zobEp[st.epSquare];
+  if (st->epSquare != SQ_NONE)
+      st->key ^= zobEp[st->epSquare];

 
 

-  st.epSquare = SQ_NONE;
-  st.rule50++;
+  st->epSquare = SQ_NONE;
+  st->rule50++;

   gamePly++;
   gamePly++;

-  st.key ^= zobSideToMove;
+  st->key ^= zobSideToMove;

 
 

-  st.mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
-  st.egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
+  st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
+  st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;

 
   assert(is_ok());
 }
 
   assert(is_ok());
 }


@@ -1481,22 +1468,22 @@ void Position::undo_null_move() {
   assert(is_ok());
   assert(!is_check());
 
   assert(is_ok());
   assert(!is_check());
 

-  // Restore information from the our UndoInfo object
-  st.lastMove = st.previous->lastMove;
-  st.epSquare = st.previous->epSquare;
-  st.previous = st.previous->previous;
+  // Restore information from the our StateInfo object
+  st->lastMove = st->previous->lastMove;
+  st->epSquare = st->previous->epSquare;
+  st->previous = st->previous->previous;

 
 

-  if (st.epSquare != SQ_NONE)
-      st.key ^= zobEp[st.epSquare];
+  if (st->epSquare != SQ_NONE)
+      st->key ^= zobEp[st->epSquare];

 
   // Update the necessary information
   sideToMove = opposite_color(sideToMove);
 
   // Update the necessary information
   sideToMove = opposite_color(sideToMove);

-  st.rule50--;
+  st->rule50--;

   gamePly--;
   gamePly--;

-  st.key ^= zobSideToMove;
+  st->key ^= zobSideToMove;

 
 

-  st.mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
-  st.egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;
+  st->mgValue += (sideToMove == WHITE)? TempoValueMidgame : -TempoValueMidgame;
+  st->egValue += (sideToMove == WHITE)? TempoValueEndgame : -TempoValueEndgame;

 
   assert(is_ok());
 }
 
   assert(is_ok());
 }


@@ -1549,7 +1536,7 @@ int Position::see(Square from, Square to) const {
   occ = occupied_squares();
 
   // Handle en passant moves
   occ = occupied_squares();
 
   // Handle en passant moves

-  if (st.epSquare == to && type_of_piece_on(from) == PAWN)
+  if (st->epSquare == to && type_of_piece_on(from) == PAWN)

   {
       assert(capture == EMPTY);
 
   {
       assert(capture == EMPTY);
 


@@ -1657,6 +1644,9 @@ int Position::see(Square from, Square to) const {
 
 void Position::clear() {
 
 
 void Position::clear() {
 

+  st = &startState;
+  st->previous = NULL; // We should never dereference this
+

   for (int i = 0; i < 64; i++)
   {
       board[i] = EMPTY;
   for (int i = 0; i < 64; i++)
   {
       board[i] = EMPTY;


@@ -1674,21 +1664,21 @@ void Position::clear() {
           pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
   }
 
           pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
   }
 

-  st.checkersBB = EmptyBoardBB;
+  st->checkersBB = EmptyBoardBB;

   for (Color c = WHITE; c <= BLACK; c++)
   for (Color c = WHITE; c <= BLACK; c++)

-      st.pinners[c] = st.pinned[c] = st.dcCandidates[c] = ~EmptyBoardBB;
-
-  st.lastMove = MOVE_NONE;
+      st->pinners[c] = st->pinned[c] = st->dcCandidates[c] = ~EmptyBoardBB;

 
   sideToMove = WHITE;
 
   sideToMove = WHITE;

-  st.castleRights = NO_CASTLES;
+  gamePly = 0;

   initialKFile = FILE_E;
   initialKRFile = FILE_H;
   initialQRFile = FILE_A;
   initialKFile = FILE_E;
   initialKRFile = FILE_H;
   initialQRFile = FILE_A;

-  st.epSquare = SQ_NONE;
-  st.rule50 = 0;
-  st.previous = NULL;
-  gamePly = 0;
+
+  st->lastMove = MOVE_NONE;
+  st->castleRights = NO_CASTLES;
+  st->epSquare = SQ_NONE;
+  st->rule50 = 0;
+  st->previous = NULL;

 }
 
 
 }
 
 


@@ -1732,7 +1722,7 @@ void Position::put_piece(Piece p, Square s) {
 
 void Position::allow_oo(Color c) {
 
 
 void Position::allow_oo(Color c) {
 

-  st.castleRights |= (1 + int(c));
+  st->castleRights |= (1 + int(c));

 }
 
 
 }
 
 


@@ -1741,7 +1731,7 @@ void Position::allow_oo(Color c) {
 
 void Position::allow_ooo(Color c) {
 
 
 void Position::allow_ooo(Color c) {
 

-  st.castleRights |= (4 + 4*int(c));
+  st->castleRights |= (4 + 4*int(c));

 }
 
 
 }
 
 


@@ -1761,7 +1751,7 @@ Key Position::compute_key() const {
   if (ep_square() != SQ_NONE)
       result ^= zobEp[ep_square()];
 
   if (ep_square() != SQ_NONE)
       result ^= zobEp[ep_square()];
 

-  result ^= zobCastle[st.castleRights];
+  result ^= zobCastle[st->castleRights];

   if (side_to_move() == BLACK)
       result ^= zobSideToMove;
 
   if (side_to_move() == BLACK)
       result ^= zobSideToMove;
 


@@ -1894,12 +1884,12 @@ bool Position::is_draw() const {
       return true;
 
   // Draw by the 50 moves rule?
       return true;
 
   // Draw by the 50 moves rule?

-  if (st.rule50 > 100 || (st.rule50 == 100 && !is_check()))
+  if (st->rule50 > 100 || (st->rule50 == 100 && !is_check()))

       return true;
 
   // Draw by repetition?
       return true;
 
   // Draw by repetition?

-  for (int i = 2; i < Min(gamePly, st.rule50); i += 2)
-      if (history[gamePly - i] == st.key)
+  for (int i = 2; i < Min(gamePly, st->rule50); i += 2)
+      if (history[gamePly - i] == st->key)

           return true;
 
   return false;
           return true;
 
   return false;


@@ -1912,21 +1902,21 @@ bool Position::is_draw() const {
 
 bool Position::has_mate_threat(Color c) {
 
 
 bool Position::has_mate_threat(Color c) {
 

-  UndoInfo u1, u2;
+  StateInfo st1, st2;

   Color stm = side_to_move();
 
   // The following lines are useless and silly, but prevents gcc from
   // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
   // be used uninitialized.
   Color stm = side_to_move();
 
   // The following lines are useless and silly, but prevents gcc from
   // emitting a stupid warning stating that u1.lastMove and u1.epSquare might
   // be used uninitialized.

-  u1.lastMove = st.lastMove;
-  u1.epSquare = st.epSquare;
+  st1.lastMove = st->lastMove;
+  st1.epSquare = st->epSquare;

 
   if (is_check())
       return false;
 
   // If the input color is not equal to the side to move, do a null move
   if (c != stm)
 
   if (is_check())
       return false;
 
   // If the input color is not equal to the side to move, do a null move
   if (c != stm)

-      do_null_move(u1);
+      do_null_move(st1);

 
   MoveStack mlist[120];
   int count;
 
   MoveStack mlist[120];
   int count;


@@ -1938,7 +1928,7 @@ bool Position::has_mate_threat(Color c) {
   // Loop through the moves, and see if one of them is mate
   for (int i = 0; i < count; i++)
   {
   // Loop through the moves, and see if one of them is mate
   for (int i = 0; i < count; i++)
   {

-      do_move(mlist[i].move, u2);
+      do_move(mlist[i].move, st2);

       if (is_mate())
           result = true;
 
       if (is_mate())
           result = true;
 


@@ -2047,20 +2037,20 @@ void Position::flipped_copy(const Position &pos) {
   castleRightsMask[make_square(initialQRFile, RANK_8)] ^=  BLACK_OOO;
 
   // En passant square
   castleRightsMask[make_square(initialQRFile, RANK_8)] ^=  BLACK_OOO;
 
   // En passant square

-  if (pos.st.epSquare != SQ_NONE)
-      st.epSquare = flip_square(pos.st.epSquare);
+  if (pos.st->epSquare != SQ_NONE)
+      st->epSquare = flip_square(pos.st->epSquare);

 
   // Checkers
   find_checkers();
 
   // Hash keys
 
   // Checkers
   find_checkers();
 
   // Hash keys

-  st.key = compute_key();
-  st.pawnKey = compute_pawn_key();
-  st.materialKey = compute_material_key();
+  st->key = compute_key();
+  st->pawnKey = compute_pawn_key();
+  st->materialKey = compute_material_key();

 
   // Incremental scores
 
   // Incremental scores

-  st.mgValue = compute_value<MidGame>();
-  st.egValue = compute_value<EndGame>();
+  st->mgValue = compute_value<MidGame>();
+  st->egValue = compute_value<EndGame>();

 
   // Material
   npMaterial[WHITE] = compute_non_pawn_material(WHITE);
 
   // Material
   npMaterial[WHITE] = compute_non_pawn_material(WHITE);


@@ -2137,7 +2127,7 @@ bool Position::is_ok(int* failedStep) const {
 
   // Is there more than 2 checkers?
   if (failedStep) (*failedStep)++;
 
   // Is there more than 2 checkers?
   if (failedStep) (*failedStep)++;

-  if (debugCheckerCount && count_1s(st.checkersBB) > 2)
+  if (debugCheckerCount && count_1s(st->checkersBB) > 2)

       return false;
 
   // Bitboards OK?
       return false;
 
   // Bitboards OK?


@@ -2172,27 +2162,27 @@ bool Position::is_ok(int* failedStep) const {
 
   // Hash key OK?
   if (failedStep) (*failedStep)++;
 
   // Hash key OK?
   if (failedStep) (*failedStep)++;

-  if (debugKey && st.key != compute_key())
+  if (debugKey && st->key != compute_key())

       return false;
 
   // Pawn hash key OK?
   if (failedStep) (*failedStep)++;
       return false;
 
   // Pawn hash key OK?
   if (failedStep) (*failedStep)++;

-  if (debugPawnKey && st.pawnKey != compute_pawn_key())
+  if (debugPawnKey && st->pawnKey != compute_pawn_key())

       return false;
 
   // Material hash key OK?
   if (failedStep) (*failedStep)++;
       return false;
 
   // Material hash key OK?
   if (failedStep) (*failedStep)++;

-  if (debugMaterialKey && st.materialKey != compute_material_key())
+  if (debugMaterialKey && st->materialKey != compute_material_key())

       return false;
 
   // Incremental eval OK?
   if (failedStep) (*failedStep)++;
   if (debugIncrementalEval)
   {
       return false;
 
   // Incremental eval OK?
   if (failedStep) (*failedStep)++;
   if (debugIncrementalEval)
   {

-      if (st.mgValue != compute_value<MidGame>())
+      if (st->mgValue != compute_value<MidGame>())

           return false;
 
           return false;
 

-      if (st.egValue != compute_value<EndGame>())
+      if (st->egValue != compute_value<EndGame>())

           return false;
   }
 
           return false;
   }
 

diff --git a/src/position.h b/src/position.h
index a7d951c3c6ec72af1abf684e2101359b5ca6d026..8d1ba3598c2da91c9252bbdf39efa3be3fea3fda 100644 (file)
--- a/src/position.h
+++ b/src/position.h
@@ -73,13 +73,12 @@ enum CastleRights {
 };
 
 
 };
 
 

-/// The UndoInfo struct stores information we need to restore a Position
+/// The StateInfo struct stores information we need to restore a Position

 /// object to its previous state when we retract a move. Whenever a move
 /// object to its previous state when we retract a move. Whenever a move

-/// is made on the board (by calling Position::do_move), an UndoInfo object
-/// must be passed as a parameter. When the move is unmade (by calling
-/// Position::undo_move), the same UndoInfo object must be passed again.
+/// is made on the board (by calling Position::do_move), an StateInfo object
+/// must be passed as a parameter.

 
 

-struct UndoInfo {
+struct StateInfo {

   Bitboard pinners[2], pinned[2], dcCandidates[2], checkersBB;
   Key key, pawnKey, materialKey;
   int castleRights, rule50;
   Bitboard pinners[2], pinned[2], dcCandidates[2], checkersBB;
   Key key, pawnKey, materialKey;
   int castleRights, rule50;


@@ -87,7 +86,7 @@ struct UndoInfo {
   Move lastMove;
   Value mgValue, egValue;
   PieceType capture;
   Move lastMove;
   Value mgValue, egValue;
   PieceType capture;

-  UndoInfo* previous;
+  StateInfo* previous;

 };
 
 
 };
 
 


@@ -241,9 +240,9 @@ public:
   bool square_is_weak(Square s, Color c) const;
 
   // Doing and undoing moves
   bool square_is_weak(Square s, Color c) const;
 
   // Doing and undoing moves

-  void do_move(Move m, UndoInfo &u);
+  void do_move(Move m, StateInfo& st);

   void undo_move(Move m);
   void undo_move(Move m);

-  void do_null_move(UndoInfo &u);
+  void do_null_move(StateInfo& st);

   void undo_null_move();
 
   // Static exchange evaluation
   void undo_null_move();
 
   // Static exchange evaluation


@@ -344,22 +343,8 @@ private:
   Key history[MaxGameLength];
   Value npMaterial[2];
   File initialKFile, initialKRFile, initialQRFile;
   Key history[MaxGameLength];
   Value npMaterial[2];
   File initialKFile, initialKRFile, initialQRFile;

-
-  // Info backed up in do_move()
-  union {
-      UndoInfo undoInfoUnion;
-      struct { // Must have the same layout of UndoInfo
-          mutable Bitboard pinners[2], pinned[2], dcCandidates[2];
-          Bitboard checkersBB;
-          Key key, pawnKey, materialKey;
-          int castleRights, rule50;
-          Square epSquare;
-          Move lastMove;
-          Value mgValue, egValue;
-          PieceType capture;
-          UndoInfo* previous;
-      } st;
-  };
+  StateInfo startState;
+  StateInfo* st;

 
   // Static variables
   static int castleRightsMask[64];
 
   // Static variables
   static int castleRightsMask[64];


@@ -510,7 +495,7 @@ inline Square Position::piece_list(Color c, PieceType pt, int index) const {
 }
 
 inline Square Position::ep_square() const {
 }
 
 inline Square Position::ep_square() const {

-  return st.epSquare;
+  return st->epSquare;

 }
 
 inline Square Position::king_square(Color c) const {
 }
 
 inline Square Position::king_square(Color c) const {


@@ -518,11 +503,11 @@ inline Square Position::king_square(Color c) const {
 }
 
 inline bool Position::can_castle_kingside(Color side) const {
 }
 
 inline bool Position::can_castle_kingside(Color side) const {

-  return st.castleRights & (1+int(side));
+  return st->castleRights & (1+int(side));

 }
 
 inline bool Position::can_castle_queenside(Color side) const {
 }
 
 inline bool Position::can_castle_queenside(Color side) const {

-  return st.castleRights & (4+4*int(side));
+  return st->castleRights & (4+4*int(side));

 }
 
 inline bool Position::can_castle(Color side) const {
 }
 
 inline bool Position::can_castle(Color side) const {


@@ -572,11 +557,11 @@ inline Bitboard Position::piece_attacks<KING>(Square s) const {
 }
 
 inline Bitboard Position::checkers() const {
 }
 
 inline Bitboard Position::checkers() const {

-  return st.checkersBB;
+  return st->checkersBB;

 }
 
 inline bool Position::is_check() const {
 }
 
 inline bool Position::is_check() const {

-  return st.checkersBB != EmptyBoardBB;
+  return st->checkersBB != EmptyBoardBB;

 }
 
 inline bool Position::pawn_attacks_square(Color c, Square f, Square t) const {
 }
 
 inline bool Position::pawn_attacks_square(Color c, Square f, Square t) const {


@@ -623,15 +608,15 @@ inline bool Position::square_is_weak(Square s, Color c) const {
 }
 
 inline Key Position::get_key() const {
 }
 
 inline Key Position::get_key() const {

-  return st.key;
+  return st->key;

 }
 
 inline Key Position::get_pawn_key() const {
 }
 
 inline Key Position::get_pawn_key() const {

-  return st.pawnKey;
+  return st->pawnKey;

 }
 
 inline Key Position::get_material_key() const {
 }
 
 inline Key Position::get_material_key() const {

-  return st.materialKey;
+  return st->materialKey;

 }
 
 template<Position::GamePhase Phase>
 }
 
 template<Position::GamePhase Phase>


@@ -646,11 +631,11 @@ inline Value Position::mg_pst_delta(Move m) const {
 }
 
 inline Value Position::mg_value() const {
 }
 
 inline Value Position::mg_value() const {

-  return st.mgValue;
+  return st->mgValue;

 }
 
 inline Value Position::eg_value() const {
 }
 
 inline Value Position::eg_value() const {

-  return st.egValue;
+  return st->egValue;

 }
 
 inline Value Position::non_pawn_material(Color c) const {
 }
 
 inline Value Position::non_pawn_material(Color c) const {


@@ -709,7 +694,7 @@ inline bool Position::move_was_passed_pawn_push(Move m) const {
 
 inline int Position::rule_50_counter() const {
 
 
 inline int Position::rule_50_counter() const {
 

-  return st.rule50;
+  return st->rule50;

 }
 
 inline bool Position::opposite_colored_bishops() const {
 }
 
 inline bool Position::opposite_colored_bishops() const {

diff --git a/src/san.cpp b/src/san.cpp
index 222a10431be9a74f5f77223376739e87172de0a5..5d5fc06c811924aeb5a7a4f2e0a37c8042cff2ac 100644 (file)
--- a/src/san.cpp
+++ b/src/san.cpp
@@ -119,9 +119,9 @@ const std::string move_to_san(const Position& pos, Move m) {
   // Is the move check?  We don't use pos.move_is_check(m) here, because
   // Position::move_is_check doesn't detect all checks (not castling moves,
   // promotions and en passant captures).
   // Is the move check?  We don't use pos.move_is_check(m) here, because
   // Position::move_is_check doesn't detect all checks (not castling moves,
   // promotions and en passant captures).

-  UndoInfo u;
+  StateInfo st;

   Position p(pos);
   Position p(pos);

-  p.do_move(m, u);
+  p.do_move(m, st);

   if (p.is_check())
       san += p.is_mate()? "#" : "+";
 
   if (p.is_check())
       san += p.is_mate()? "#" : "+";
 


@@ -290,7 +290,7 @@ Move move_from_san(const Position& pos, const std::string& movestr) {
 
 const std::string line_to_san(const Position& pos, Move line[], int startColumn, bool breakLines) {
 
 
 const std::string line_to_san(const Position& pos, Move line[], int startColumn, bool breakLines) {
 

-  UndoInfo u;
+  StateInfo st;

   std::stringstream s;
   std::string moveStr;
   size_t length = 0;
   std::stringstream s;
   std::string moveStr;
   size_t length = 0;


@@ -309,9 +309,9 @@ const std::string line_to_san(const Position& pos, Move line[], int startColumn,
       s << moveStr << ' ';
 
       if (line[i] == MOVE_NULL)
       s << moveStr << ' ';
 
       if (line[i] == MOVE_NULL)

-          p.do_null_move(u);
+          p.do_null_move(st);

       else
       else

-          p.do_move(line[i], u);
+          p.do_move(line[i], st);

   }
   return s.str();
 }
   }
   return s.str();
 }

diff --git a/src/search.cpp b/src/search.cpp
index 8c847714150b7d74668f73a1ef2833f29c311b03..2b41ec448da40db166b8a107e7a529ddc0a491e1 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -753,12 +753,12 @@ namespace {
         if (dbg_show_hit_rate)
             dbg_print_hit_rate(LogFile);
 
         if (dbg_show_hit_rate)
             dbg_print_hit_rate(LogFile);
 

-        UndoInfo u;
+        StateInfo st;

         LogFile << "Nodes: " << nodes_searched() << std::endl
                 << "Nodes/second: " << nps() << std::endl
                 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
 
         LogFile << "Nodes: " << nodes_searched() << std::endl
                 << "Nodes/second: " << nps() << std::endl
                 << "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
 

-        p.do_move(ss[0].pv[0], u);
+        p.do_move(ss[0].pv[0], st);

         LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
                 << std::endl << std::endl;
     }
         LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
                 << std::endl << std::endl;
     }


@@ -781,7 +781,7 @@ namespace {
     {
         int64_t nodes;
         Move move;
     {
         int64_t nodes;
         Move move;

-        UndoInfo u;
+        StateInfo st;

         Depth ext, newDepth;
 
         RootMoveNumber = i + 1;
         Depth ext, newDepth;
 
         RootMoveNumber = i + 1;


@@ -807,7 +807,7 @@ namespace {
         newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
 
         // Make the move, and search it
         newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
 
         // Make the move, and search it

-        pos.do_move(move, u);
+        pos.do_move(move, st);

 
         if (i < MultiPV)
         {
 
         if (i < MultiPV)
         {


@@ -1011,8 +1011,8 @@ namespace {
       Depth newDepth = depth - OnePly + ext;
 
       // Make and search the move
       Depth newDepth = depth - OnePly + ext;
 
       // Make and search the move

-      UndoInfo u;
-      pos.do_move(move, u);
+      StateInfo st;
+      pos.do_move(move, st);

 
       if (moveCount == 1) // The first move in list is the PV
           value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
 
       if (moveCount == 1) // The first move in list is the PV
           value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);


@@ -1182,8 +1182,8 @@ namespace {
     {
         ss[ply].currentMove = MOVE_NULL;
 
     {
         ss[ply].currentMove = MOVE_NULL;
 

-        UndoInfo u;
-        pos.do_null_move(u);
+        StateInfo st;
+        pos.do_null_move(st);

         int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
 
         Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
         int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
 
         Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);


@@ -1334,8 +1334,8 @@ namespace {
       }
 
       // Make and search the move
       }
 
       // Make and search the move

-      UndoInfo u;
-      pos.do_move(move, u);
+      StateInfo st;
+      pos.do_move(move, st);

 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.


@@ -1513,8 +1513,8 @@ namespace {
           continue;
 
       // Make and search the move.
           continue;
 
       // Make and search the move.

-      UndoInfo u;
-      pos.do_move(move, u);
+      StateInfo st;
+      pos.do_move(move, st);

       Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
       pos.undo_move(move);
 
       Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
       pos.undo_move(move);
 


@@ -1605,8 +1605,8 @@ namespace {
         continue;
 
       // Make and search the move.
         continue;
 
       // Make and search the move.

-      UndoInfo u;
-      pos.do_move(move, u);
+      StateInfo st;
+      pos.do_move(move, st);

 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.


@@ -1714,8 +1714,8 @@ namespace {
       Depth newDepth = sp->depth - OnePly + ext;
 
       // Make and search the move.
       Depth newDepth = sp->depth - OnePly + ext;
 
       // Make and search the move.

-      UndoInfo u;
-      pos.do_move(move, u);
+      StateInfo st;
+      pos.do_move(move, st);

 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.


@@ -1876,12 +1876,12 @@ namespace {
         if (includeMove)
         {
             // Find a quick score for the move
         if (includeMove)
         {
             // Find a quick score for the move

-            UndoInfo u;
+            StateInfo st;

             SearchStack ss[PLY_MAX_PLUS_2];
 
             moves[count].move = mlist[i].move;
             moves[count].nodes = 0ULL;
             SearchStack ss[PLY_MAX_PLUS_2];
 
             moves[count].move = mlist[i].move;
             moves[count].nodes = 0ULL;

-            pos.do_move(moves[count].move, u);
+            pos.do_move(moves[count].move, st);

             moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
                                           Depth(0), 1, 0);
             pos.undo_move(moves[count].move);
             moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
                                           Depth(0), 1, 0);
             pos.undo_move(moves[count].move);

diff --git a/src/tt.cpp b/src/tt.cpp
index a8f871465bb46224ddfbe220001ab0e53bf5b6c7..8911e171eea429cabcb6be99ce202ef09a768bd5 100644 (file)
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -177,13 +177,13 @@ void TranspositionTable::new_search() {
 
 void TranspositionTable::insert_pv(const Position &pos, Move pv[]) {
 
 
 void TranspositionTable::insert_pv(const Position &pos, Move pv[]) {
 

-  UndoInfo u;
+  StateInfo st;

   Position p(pos);
 
   for (int i = 0; pv[i] != MOVE_NONE; i++)
   {
     store(p, VALUE_NONE, Depth(0), pv[i], VALUE_TYPE_NONE);
   Position p(pos);
 
   for (int i = 0; pv[i] != MOVE_NONE; i++)
   {
     store(p, VALUE_NONE, Depth(0), pv[i], VALUE_TYPE_NONE);

-    p.do_move(pv[i], u);
+    p.do_move(pv[i], st);

   }
 }
 
   }
 }
 

diff --git a/src/uci.cpp b/src/uci.cpp
index 4aade3b66bb99cbcdb261089519443f7c8e48c11..b03752edc4220e865d4087642e1523e53050d42a 100644 (file)
--- a/src/uci.cpp
+++ b/src/uci.cpp
@@ -219,12 +219,12 @@ namespace {
         if (token == "moves")
         {
             Move move;
         if (token == "moves")
         {
             Move move;

-            UndoInfo u;
+            StateInfo st;

             while (!uip.eof())
             {
                 uip >> token;
                 move = move_from_string(RootPosition, token);
             while (!uip.eof())
             {
                 uip >> token;
                 move = move_from_string(RootPosition, token);

-                RootPosition.do_move(move, u);
+                RootPosition.do_move(move, st);

                 if (RootPosition.rule_50_counter() == 0)
                     RootPosition.reset_game_ply();
             }
                 if (RootPosition.rule_50_counter() == 0)
                     RootPosition.reset_game_ply();
             }