Double probability of using classical eval

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 09f36513047c05b873cd9b6850a5d9d4d52103db..faf71d2701dd83ad152e2d82f260750a904e5809 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1015,12 +1015,19 @@ make_v:
 
 Value Eval::evaluate(const Position& pos) {
 
+  // Use classical eval if there is a large imbalance
+  // If there is a moderate imbalance, use classical eval with probability (1/8),
+  // as derived from the node counter.
+  bool useClassical = abs(eg_value(pos.psq_score())) * 16 > NNUEThreshold1 * (16 + pos.rule50_count());
   bool classical = !Eval::useNNUE
-                ||  abs(eg_value(pos.psq_score())) * 16 > NNUEThreshold1 * (16 + pos.rule50_count());
+                ||  useClassical
+                || (abs(eg_value(pos.psq_score())) > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB));
   Value v = classical ? Evaluation<NO_TRACE>(pos).value()
                       : NNUE::evaluate(pos) * 5 / 4 + Tempo;
 
-  if (classical && Eval::useNNUE && abs(v) * 16 < NNUEThreshold2 * (16 + pos.rule50_count()))
+  if (   useClassical 
+      && Eval::useNNUE 
+      && abs(v) * 16 < NNUEThreshold2 * (16 + pos.rule50_count()))
       v = NNUE::evaluate(pos) * 5 / 4 + Tempo;
 
   // Damp down the evaluation linearly when shuffling