Tweak nnue scaling to keep more material

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index db8379da34f8652bae813885629f91e9332e8a26..710898bc15d5929eed398c4dd120e80cf50b3f6a 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -60,7 +60,7 @@ namespace Eval {
   bool useNNUE;
   string eval_file_loaded = "None";
 
-  /// init_NNUE() tries to load a nnue network at startup time, or when the engine
+  /// NNUE::init() tries to load a nnue network at startup time, or when the engine
   /// receives a UCI command "setoption name EvalFile value nn-[a-z0-9]{12}.nnue"
   /// The name of the nnue network is always retrieved from the EvalFile option.
   /// We search the given network in three locations: internally (the default
@@ -68,7 +68,7 @@ namespace Eval {
   /// in the engine directory. Distro packagers may define the DEFAULT_NNUE_DIRECTORY
   /// variable to have the engine search in a special directory in their distro.
 
-  void init_NNUE() {
+  void NNUE::init() {
 
     useNNUE = Options["Use NNUE"];
     if (!useNNUE)
@@ -111,8 +111,8 @@ namespace Eval {
         }
   }
 
-  /// verify_NNUE() verifies that the last net used was loaded successfully
-  void verify_NNUE() {
+  /// NNUE::verify() verifies that the last net used was loaded successfully
+  void NNUE::verify() {
 
     string eval_file = string(Options["EvalFile"]);
 
@@ -1015,17 +1015,36 @@ make_v:
 
 Value Eval::evaluate(const Position& pos) {
 
-  bool useClassical = abs(eg_value(pos.psq_score())) * 16 > NNUEThreshold1 * (16 + pos.rule50_count());
-  bool classical = !Eval::useNNUE
-                ||  useClassical
-                || (abs(eg_value(pos.psq_score())) > PawnValueMg / 8 && !(pos.this_thread()->nodes & 0xF));
-  Value v = classical ? Evaluation<NO_TRACE>(pos).value()
-                      : NNUE::evaluate(pos) * 5 / 4 + Tempo;
-
-  if (   useClassical 
-      && Eval::useNNUE 
-      && abs(v) * 16 < NNUEThreshold2 * (16 + pos.rule50_count()))
-      v = 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 = [&](){
+         int mat = pos.non_pawn_material();
+         return NNUE::evaluate(pos) * (1024 + mat / 32) / 1024 + 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.
+      // 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
+          && (abs(v) * 16 < NNUEThreshold2 * r50
+          || (   pos.opposite_bishops()
+              && abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50
+              && !(pos.this_thread()->nodes & 0xB))))
+          v = adjusted_NNUE();
+  }
 
   // Damp down the evaluation linearly when shuffling
   v = v * (100 - pos.rule50_count()) / 100;