Adjust singular extension depth restriction

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 99c4743174dfbb9befae87b2fecca958b2450107..cded8614ad9d6c77851b5b71db034ec96baa0e38 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1089,7 +1089,7 @@ moves_loop: // When in check, search starts here
       // a reduced search on all the other moves but the ttMove and if the
       // result is lower than ttValue minus a margin, then we will extend the ttMove.
       if (   !rootNode
-          &&  depth >= 7
+          &&  depth >= 6 + 2 * (PvNode && tte->is_pv())
           &&  move == ttMove
           && !excludedMove // Avoid recursive singular search
        /* &&  ttValue != VALUE_NONE Already implicit in the next condition */
@@ -1165,6 +1165,8 @@ moves_loop: // When in check, search starts here
       // Step 15. Make the move
       pos.do_move(move, st, givesCheck);
 
+      bool doDeeperSearch = false;
+
       // Step 16. Late moves reduction / extension (LMR, ~200 Elo)
       // We use various heuristics for the sons of a node after the first son has
       // been searched. In general we would like to reduce them, but there are many
@@ -1237,6 +1239,7 @@ moves_loop: // When in check, search starts here
 
           // If the son is reduced and fails high it will be re-searched at full depth
           doFullDepthSearch = value > alpha && d < newDepth;
+          doDeeperSearch = value > alpha + 88;
           didLMR = true;
       }
       else
@@ -1248,7 +1251,7 @@ moves_loop: // When in check, search starts here
       // Step 17. Full depth search when LMR is skipped or fails high
       if (doFullDepthSearch)
       {
-          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
 
           // If the move passed LMR update its stats
           if (didLMR && !captureOrPromotion)
@@ -1380,7 +1383,15 @@ moves_loop: // When in check, search starts here
     // Bonus for prior countermove that caused the fail low
     else if (   (depth >= 3 || PvNode)
              && !priorCapture)
-        update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + (PvNode || cutNode)));
+    {
+        //Assign extra bonus if current node is PvNode or cutNode
+        //or fail low was really bad
+        bool extraBonus =    PvNode
+                          || cutNode
+                          || bestValue < alpha - 94 * depth;
+
+        update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus));
+    }
 
     if (PvNode)
         bestValue = std::min(bestValue, maxValue);