Use pure NNUE for king of the hill

Since the best NNUE network is much stronger than classical evaluation,
it seems intuitive to switch from hybrid to pure NNUE evaluation.

kingofthehill STC
Score: 133 - 34 - 33  [0.748] 200
Elo: 188.5 +/- 49.5, LOS: 100.0 %, DrawRatio: 16.5 %

kingofthehill LTC
Score: 63 - 20 - 17  [0.715] 100
Elo: 159.8 +/- 68.4, LOS: 100.0 %, DrawRatio: 17.0 %

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 0efda47..17b8a83 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1476,8 +1476,9 @@ Value Eval::evaluate(const Position& pos) {
       // 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));
+      bool  pure = pos.capture_the_flag_piece() && pos.checking_permitted();
+      bool  largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50 && !pure;
+      bool  classical = largePsq || (psq > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB) && !pure);
 
       v = classical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();