X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=588f76f3e6b789c6d8d500c56aba12eaf61718c7;hp=29b7c5f3ebab93a78b832a23905a0e07af535800;hb=9645e8e4e76aebc4b3099b20846c14e18768cab4;hpb=935fc09fd49328adfeaad372a5f4f2c48d8caf44

diff --git a/src/search.cpp b/src/search.cpp
index 29b7c5f3..588f76f3 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -198,7 +198,7 @@ namespace {
   Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
 
   // Minimum depth for use of singular extension
-  const Depth SingularExtensionDepth[2] = { 8 * OnePly /* non-PV */, 6 * OnePly /* PV */};
+  const Depth SingularExtensionDepth[2] = { 7 * OnePly /* non-PV */, 6 * OnePly /* PV */};
 
   // If the TT move is at least SingularExtensionMargin better then the
   // remaining ones we will extend it.
@@ -1213,6 +1213,17 @@ namespace {
                            && is_lower_bound(tte->type())
                            && tte->depth() >= depth - 3 * OnePly;
 
+    // Avoid to do an expensive singular extension search on nodes where
+    // such search had already failed in the past.
+    if (  !PvNode
+        && singularExtensionNode
+        && depth < SingularExtensionDepth[PvNode] + 5 * OnePly)
+    {
+        TTEntry* ttx = TT.retrieve(pos.get_exclusion_key());
+        if (ttx && is_lower_bound(ttx->type()))
+            singularExtensionNode = false;
+    }
+
     // Step 10. Loop through moves
     // Loop through all legal moves until no moves remain or a beta cutoff occurs
     while (   bestValue < beta