Tweak hybrid treshold.

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 09f36513047c05b873cd9b6850a5d9d4d52103db..a9159477a077fd626f9acc584292307b985b4cbf 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1015,13 +1015,28 @@ make_v:
 
 Value Eval::evaluate(const Position& pos) {
 
-  bool classical = !Eval::useNNUE
-                ||  abs(eg_value(pos.psq_score())) * 16 > NNUEThreshold1 * (16 + pos.rule50_count());
-  Value v = classical ? Evaluation<NO_TRACE>(pos).value()
-                      : NNUE::evaluate(pos) * 5 / 4 + Tempo;
+  Value v;
+
+  if (!Eval::useNNUE)
+      v = Evaluation<NO_TRACE>(pos).value();
+  else
+  {
+      // scale and shift NNUE for compatibility with search and classical evaluation
+      auto  adjusted_NNUE = [&](){ return NNUE::evaluate(pos) * 5 / 4 + Tempo; };
 
-  if (classical && Eval::useNNUE && abs(v) * 16 < NNUEThreshold2 * (16 + pos.rule50_count()))
-      v = NNUE::evaluate(pos) * 5 / 4 + Tempo;
+      // if there is PSQ imbalance use classical eval, with small probability if it is small
+      Value psq = Value(abs(eg_value(pos.psq_score())));
+      int   r50 = 16 + pos.rule50_count();
+      bool  largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
+      bool  classical = largePsq || (psq > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB));
+
+      v = classical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();
+
+      // if the classical eval is small and imbalance large, use NNUE nevertheless.
+      if (   largePsq
+          && abs(v) * 16 < NNUEThreshold2 * r50)
+          v = adjusted_NNUE();
+  }
 
   // Damp down the evaluation linearly when shuffling
   v = v * (100 - pos.rule50_count()) / 100;