Score non-captures only by history

[stockfish] / src / movepick.cpp

diff --git a/src/movepick.cpp b/src/movepick.cpp
index ea332b7be37b4ae4b73be30ea8fa9277d5660ff2..901aa60e5625c766b797fd88d4dec2888b24ac69 100644 (file)
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -74,7 +74,6 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
                        const History& h, SearchStack* ss) : pos(p), H(h) {
   int searchTT = ttm;
   ttMoves[0].move = ttm;
-  finished = false;
   lastBadCapture = badCaptures;
 
   pinned = p.pinned_pieces(pos.side_to_move());
@@ -95,8 +94,16 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
   else if (d == Depth(0))
       phasePtr = QsearchWithChecksPhaseTable;
   else
+  {
       phasePtr = QsearchWithoutChecksPhaseTable;
 
+      // Skip TT move if is not a capture or a promotion, this avoids
+      // qsearch tree explosion due to a possible perpetual check or
+      // similar rare cases when TT table is full.
+      if (ttm != MOVE_NONE && !pos.move_is_capture_or_promotion(ttm))
+          searchTT = ttMoves[0].move = MOVE_NONE;
+  }
+
   phasePtr += !searchTT - 1;
   go_next_phase();
 }
@@ -142,7 +149,7 @@ void MovePicker::go_next_phase() {
   case PH_EVASIONS:
       assert(pos.is_check());
       lastMove = generate_evasions(pos, moves);
-      score_evasions();
+      score_evasions_or_checks();
       return;
 
   case PH_QCAPTURES:
@@ -151,12 +158,12 @@ void MovePicker::go_next_phase() {
       return;
 
   case PH_QCHECKS:
-      // Perhaps we should order moves move here?  FIXME
       lastMove = generate_non_capture_checks(pos, moves);
+      score_evasions_or_checks();
       return;
 
   case PH_STOP:
-      lastMove = curMove + 1; // hack to be friendly for get_next_move()
+      lastMove = curMove + 1; // Avoids another go_next_phase() call
       return;
 
   default:
@@ -206,7 +213,6 @@ void MovePicker::score_noncaptures() {
   Move m;
   Piece piece;
   Square from, to;
-  int hs;
 
   for (MoveStack* cur = moves; cur != lastMove; cur++)
   {
@@ -214,18 +220,11 @@ void MovePicker::score_noncaptures() {
       from = move_from(m);
       to = move_to(m);
       piece = pos.piece_on(from);
-      hs = H.move_ordering_score(piece, to);
-
-      // Ensure history is always preferred to pst
-      if (hs > 0)
-          hs += 1000;
-
-      // pst based scoring
-      cur->score = hs + mg_value(pos.pst_delta(piece, from, to));
+      cur->score = H.move_ordering_score(piece, to);
   }
 }
 
-void MovePicker::score_evasions() {
+void MovePicker::score_evasions_or_checks() {
   // Try good captures ordered by MVV/LVA, then non-captures if
   // destination square is not under attack, ordered by history
   // value, and at the end bad-captures and non-captures with a
@@ -233,6 +232,10 @@ void MovePicker::score_evasions() {
   Move m;
   int seeScore;
 
+  // Skip if we don't have at least two moves to order
+  if (lastMove < moves + 2)
+      return;
+
   for (MoveStack* cur = moves; cur != lastMove; cur++)
   {
       m = cur->move;
@@ -251,6 +254,8 @@ void MovePicker::score_evasions() {
 /// are no more moves left.
 /// It picks the move with the biggest score from a list of generated moves taking
 /// care not to return the tt move if has already been searched previously.
+/// Note that this function is not thread safe so should be lock protected by
+/// caller when accessed through a shared MovePicker object.
 
 Move MovePicker::get_next_move() {
 
@@ -340,21 +345,3 @@ Move MovePicker::get_next_move() {
   }
 }
 
-/// A variant of get_next_move() which takes a lock as a parameter, used to
-/// prevent multiple threads from picking the same move at a split point.
-
-Move MovePicker::get_next_move(Lock &lock) {
-
-   lock_grab(&lock);
-   if (finished)
-   {
-       lock_release(&lock);
-       return MOVE_NONE;
-   }
-   Move m = get_next_move();
-   if (m == MOVE_NONE)
-       finished = true;
-
-   lock_release(&lock);
-   return m;
-}