Use past SE information also for success cases

If singular extension search was succesful in the past then
skip another the SE search and extend of one ply.

Another way to mitigate the cost of SE at the price of
some more spurious extension, but on 90% of cases info
is correct.

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

diff --git a/src/search.cpp b/src/search.cpp
index b1f64536f6db51f1a09b8982a31ae7dc35ef1476..58feb77d7038fc49dcb24821dbf9b762fa84925c 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -979,7 +979,7 @@ namespace {
     Move movesSearched[256];
     EvalInfo ei;
     StateInfo st;
     Move movesSearched[256];
     EvalInfo ei;
     StateInfo st;

-    const TTEntry* tte;
+    const TTEntry *tte, *ttx;

     Key posKey;
     Move ttMove, move, excludedMove, threatMove;
     Depth ext, newDepth;
     Key posKey;
     Move ttMove, move, excludedMove, threatMove;
     Depth ext, newDepth;


@@ -1190,17 +1190,6 @@ namespace {
                            && is_lower_bound(tte->type())
                            && tte->depth() >= depth - 3 * OnePly;
 
                            && 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
     // Step 10. Loop through moves
     // Loop through all legal moves until no moves remain or a beta cutoff occurs
     while (   bestValue < beta


@@ -1226,9 +1215,22 @@ namespace {
           && move == tte->move()
           && ext < OnePly)
       {
           && move == tte->move()
           && ext < OnePly)
       {

+          // Avoid to do an expensive singular extension search on nodes where
+          // such search have already been done in the past, so assume the last
+          // singular extension search result is still valid.
+          if (  !PvNode
+              && depth < SingularExtensionDepth[PvNode] + 5 * OnePly
+              && ((ttx = TT.retrieve(pos.get_exclusion_key())) != NULL))
+          {
+              if (is_upper_bound(ttx->type()))
+                  ext = OnePly;
+
+              singularExtensionNode = false;
+          }
+

           Value ttValue = value_from_tt(tte->value(), ply);
 
           Value ttValue = value_from_tt(tte->value(), ply);
 

-          if (abs(ttValue) < VALUE_KNOWN_WIN)
+          if (singularExtensionNode && abs(ttValue) < VALUE_KNOWN_WIN)

           {
               Value b = ttValue - SingularExtensionMargin;
               ss->excludedMove = move;
           {
               Value b = ttValue - SingularExtensionMargin;
               ss->excludedMove = move;