Also dampen NNUE eval with 50 move rule

Move the existing dampening function last so that NNUE evaluations are
also handled as we approach the 50 move rule.

STC:
LLR: 2.95 (-2.94,2.94) {-0.50,1.50}
Total: 4792 W: 695 L: 561 D: 3536
Ptnml(0-2): 19, 420, 1422, 478, 57
https://tests.stockfishchess.org/tests/view/5f3164179081672066537534

LTC:
LLR: 8.62 (-2.94,2.94) {0.25,1.75}
Total: 286744 W: 18494 L: 17430 D: 250820
Ptnml(0-2): 418, 14886, 111745, 15860, 463
https://tests.stockfishchess.org/tests/view/5f316b039081672066537541

closes https://github.com/official-stockfish/Stockfish/pull/3004

Bench: 4001800

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index caab2979d35075ad7e7da1962df3fb01f353e5fb..00fd2005ed7445008263db7f71c547c72a3ef997 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -927,9 +927,6 @@ make_v:
     // Side to move point of view
     v = (pos.side_to_move() == WHITE ? v : -v) + Tempo;
 
-    // Damp down the evaluation linearly when shuffling
-    v = v * (100 - pos.rule50_count()) / 100;
-
     return v;
   }
 
@@ -941,14 +938,15 @@ make_v:
 
 Value Eval::evaluate(const Position& pos) {
 
-  if (Eval::useNNUE)
-  {
-      Value v = eg_value(pos.psq_score());
-      // Take NNUE eval only on balanced positions
-      if (abs(v) < NNUEThreshold)
-         return NNUE::evaluate(pos) + Tempo;
-  }
-  return Evaluation<NO_TRACE>(pos).value();
+  bool classical = !Eval::useNNUE
+                ||  abs(eg_value(pos.psq_score())) >= NNUEThreshold;
+  Value v = classical ? Evaluation<NO_TRACE>(pos).value()
+                      : NNUE::evaluate(pos) + Tempo;
+
+  // Damp down the evaluation linearly when shuffling
+  v = v * (100 - pos.rule50_count()) / 100;
+
+  return v;
 }
 
 /// trace() is like evaluate(), but instead of returning a value, it returns