Don't prune TT move in qsearch even if SEE < 0

Even if SEE is negative there is always a good possibility that TT move is a cut move anyway. For instance a lot of BXN exchanges that have negative SEE can very easily be good exchanges. A nice side effect is a bit reduced frequency of see_sign() calls. After 643 games at 1+0 Mod vs Orig +174 =327 -142 52.49% 337.5/643 +17 ELO Signed-off-by: Marco Costalba <mcostalba@gmail.com>
mcostalba · Oct 22, 2009 · a72c552 · a72c552
1 parent cf4df03
commit a72c552
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/src/search.cpp b/src/search.cpp
@@ -1596,6 +1596,7 @@ namespace {
 
       // Don't search captures and checks with negative SEE values
       if (   !isCheck
+          &&  move != ttMove
           && !move_is_promotion(move)
           &&  pos.see_sign(move) < 0)
           continue;
@@ -1622,7 +1623,7 @@ namespace {
 
     // All legal moves have been searched.  A special case: If we're in check
     // and no legal moves were found, it is checkmate.
-    if (pos.is_check() && moveCount == 0) // Mate!
+    if (!moveCount && pos.is_check()) // Mate!
         return value_mated_in(ply);
 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);