Do more reductions at Pv nodes with low delta

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 075be835a1aa575f624b1fa2418815b54f67b6c5..46c95ef0979d89e8d856e5c79e9d902b224d19dd 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -625,6 +625,8 @@ namespace {
         if (alpha >= beta)
             return alpha;
     }
+    else
+        thisThread->rootDelta = beta - alpha;
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
@@ -813,7 +815,7 @@ namespace {
     if (   !PvNode
         &&  depth < 9
         &&  eval - futility_margin(depth, improving) >= beta
-        &&  eval < VALUE_KNOWN_WIN) // Do not return unproven wins
+        &&  eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
         return eval;
 
     // Step 8. Null move search with verification search (~40 Elo)
@@ -1167,6 +1169,10 @@ moves_loop: // When in check, search starts here
               && bestMoveCount <= 3)
               r--;
 
+          // Increases reduction for PvNodes that have small window
+          if (PvNode && beta - alpha < thisThread->rootDelta / 4)
+              r++;
+
           // Decrease reduction if position is or has been on the PV
           // and node is not likely to fail low. (~3 Elo)
           if (   ss->ttPv