use classical for certain endgames.

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 3d8871191f96f0180fd2d98a95dcf6dd0a4e6dd8..90d11a00fd886fe5ee78e185382be71fa70264de 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1035,12 +1035,14 @@ Value Eval::evaluate(const Position& pos) {
       bool  largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
       bool  classical = largePsq || (psq > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB));
 
       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();
+      bool strongClassical = pos.non_pawn_material() < 2 * RookValueMg && pos.count<PAWN>() < 2;
+
+      v = classical || strongClassical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();

 
       // If the classical eval is small and imbalance large, use NNUE nevertheless.
       // For the case of opposite colored bishops, switch to NNUE eval with
       // small probability if the classical eval is less than the threshold.
 
       // If the classical eval is small and imbalance large, use NNUE nevertheless.
       // For the case of opposite colored bishops, switch to NNUE eval with
       // small probability if the classical eval is less than the threshold.

-      if (   largePsq
+      if (   largePsq && !strongClassical

           && (   abs(v) * 16 < NNUEThreshold2 * r50
               || (   pos.opposite_bishops()
                   && abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50
           && (   abs(v) * 16 < NNUEThreshold2 * r50
               || (   pos.opposite_bishops()
                   && abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50