Add psqt ordering when there is no history

This seems to increase strenght (about 15 ELO),
still to test some variations on this theme that
could increase ELO even more.

Idea from Rebel (http://members.home.nl/matador/chess840.htm)

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

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 4d2d31167ea2db2641c582c545ba3c6c46b1a0fe..d0ceaf1c23e8166263e88d10401c035e9cc0d2e5 100644 (file)
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -246,15 +246,36 @@ void MovePicker::score_captures() {
 }
 
 void MovePicker::score_noncaptures() {
-  for(int i = 0; i < numOfMoves; i++) {
-    Move m = moves[i].move;
-    if(m == killer1)
-      moves[i].score = HistoryMax + 2;
-    else if(m == killer2)
-      moves[i].score = HistoryMax + 1;
-    else
-      moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
+
+  bool all_zero = true;
+  for (int i = 0; i < numOfMoves; i++)
+  {
+      Move m = moves[i].move;
+      if (m == killer1)
+      {
+          moves[i].score = HistoryMax + 2;
+          all_zero = false;
+      }
+      else if (m == killer2)
+      {
+          moves[i].score = HistoryMax + 1;
+          all_zero = false;
+      }
+      else
+      {
+          moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
+          if (all_zero && moves[i].score != 0)
+              all_zero = false;
+      }
   }
+  if (!all_zero)
+      return;
+
+  // If we don't have at least one history score then
+  // try to order using psq tables difference between 
+  // from square and to square.
+  for (int i = 0; i < numOfMoves; i++)
+      moves[i].score = pos->mg_pst_delta(moves[i].move);
 }
 
 void MovePicker::score_evasions() {

diff --git a/src/position.h b/src/position.h
index 9acb29669e1633fe76159abcf5ea8241f4e3f8c8..25596bf6a2add681047ef5085006cb3640782dff 100644 (file)
--- a/src/position.h
+++ b/src/position.h
@@ -278,6 +278,7 @@ public:
   Value eg_value() const;
   Value non_pawn_material(Color c) const;
   Phase game_phase() const;
+  Value mg_pst_delta(Move m) const;
 
   // Game termination checks
   bool is_mate();
@@ -681,6 +682,11 @@ inline Value Position::mg_pst(Color c, PieceType pt, Square s) const {
   return MgPieceSquareTable[piece_of_color_and_type(c, pt)][s];
 }
 
+inline Value Position::mg_pst_delta(Move m) const {
+  return MgPieceSquareTable[piece_on(move_from(m))][move_to(m)]
+        -MgPieceSquareTable[piece_on(move_from(m))][move_from(m)];
+}
+
 inline Value Position::eg_pst(Color c, PieceType pt, Square s) const {
   return EgPieceSquareTable[piece_of_color_and_type(c, pt)][s];
 }