Simplify blending nnue complexity with optimism

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 99b873004edfd6043b3f9c62add579ca422b2897..bf6dd69a950282588c904d5f60b0305f9eb9b319 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -82,8 +82,6 @@ namespace Eval {
         eval_file = EvalFileDefaultName;
 
     #if defined(DEFAULT_NNUE_DIRECTORY)
-    #define stringify2(x) #x
-    #define stringify(x) stringify2(x)
     vector<string> dirs = { "<internal>" , "" , CommandLine::binaryDirectory , stringify(DEFAULT_NNUE_DIRECTORY) };
     #else
     vector<string> dirs = { "<internal>" , "" , CommandLine::binaryDirectory };
@@ -1048,39 +1046,33 @@ make_v:
 /// evaluate() is the evaluator for the outer world. It returns a static
 /// evaluation of the position from the point of view of the side to move.
 
-Value Eval::evaluate(const Position& pos, int* complexity) {
+Value Eval::evaluate(const Position& pos) {
+
+  assert(!pos.checkers());
 
   Value v;
   Value psq = pos.psq_eg_stm();
 
   // We use the much less accurate but faster Classical eval when the NNUE
   // option is set to false. Otherwise we use the NNUE eval unless the
-  // PSQ advantage is decisive and several pieces remain. (~3 Elo)
-  bool useClassical = !useNNUE || (pos.count<ALL_PIECES>() > 7 && abs(psq) > 1781);
+  // PSQ advantage is decisive. (~4 Elo at STC, 1 Elo at LTC)
+  bool useClassical = !useNNUE || abs(psq) > 2048;
 
   if (useClassical)
       v = Evaluation<NO_TRACE>(pos).value();
   else
   {
       int nnueComplexity;
-      int scale = 1001 + 5 * pos.count<PAWN>() + 61 * pos.non_pawn_material() / 4096;
+      int npm = pos.non_pawn_material() / 64;
 
       Color stm = pos.side_to_move();
       Value optimism = pos.this_thread()->optimism[stm];
 
       Value nnue = NNUE::evaluate(pos, true, &nnueComplexity);
 
-      // Blend nnue complexity with (semi)classical complexity
-      nnueComplexity = (  406 * nnueComplexity
-                        + (424 + optimism) * abs(psq - nnue)
-                        ) / 1024;
-
-      // Return hybrid NNUE complexity to caller
-      if (complexity)
-          *complexity = nnueComplexity;
-
-      optimism = optimism * (272 + nnueComplexity) / 256;
-      v = (nnue * scale + optimism * (scale - 748)) / 1024;
+      // Blend optimism with nnue complexity and (semi)classical complexity
+      optimism += 25 * optimism * (nnueComplexity + abs(psq - nnue)) / 16384;
+      v = (nnue * (945 + npm) + optimism * (174 + npm)) / 1024;
   }
 
   // Damp down the evaluation linearly when shuffling
@@ -1089,10 +1081,6 @@ Value Eval::evaluate(const Position& pos, int* complexity) {
   // Guarantee evaluation does not hit the tablebase range
   v = std::clamp(v, VALUE_TB_LOSS_IN_MAX_PLY + 1, VALUE_TB_WIN_IN_MAX_PLY - 1);
 
-  // When not using NNUE, return classical complexity to caller
-  if (complexity && useClassical)
-      *complexity = abs(v - psq);
-
   return v;
 }