Fallback to NNUE

If the classical eval ends up much smaller than estimated fall back to NNUE.
Also use multiply instead of divide for the threshold comparison for smoother transitions without rounding.

STC https://tests.stockfishchess.org/tests/view/5f3a5011b38d442594aabdfe
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 57352 W: 6325 L: 6135 D: 44892
Ptnml(0-2): 277, 4748, 18482, 4846, 323

LTC https://tests.stockfishchess.org/tests/view/5f3aee9db38d442594aabe82
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 16232 W: 897 L: 781 D: 14554
Ptnml(0-2): 19, 679, 6616, 771, 31

closes https://github.com/official-stockfish/Stockfish/pull/3023

bench: 4026216

-----

Recommended net: https://tests.stockfishchess.org/api/nn/nn-82215d0fd0df.nnue

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 3a620a78305fb83da36f9b9b5278be919cf685aa..1bd893533bb082f0d9a006d8c5cd22f764c5b619 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -114,7 +114,8 @@ namespace {
   constexpr Value LazyThreshold1 =  Value(1400);
   constexpr Value LazyThreshold2 =  Value(1300);
   constexpr Value SpaceThreshold = Value(12222);
   constexpr Value LazyThreshold1 =  Value(1400);
   constexpr Value LazyThreshold2 =  Value(1300);
   constexpr Value SpaceThreshold = Value(12222);

-  constexpr Value NNUEThreshold  =   Value(575);
+  constexpr Value NNUEThreshold1 =   Value(550);
+  constexpr Value NNUEThreshold2 =   Value(150);

 
   // KingAttackWeights[PieceType] contains king attack weights by piece type
   constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
 
   // KingAttackWeights[PieceType] contains king attack weights by piece type
   constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };


@@ -939,10 +940,13 @@ make_v:
 Value Eval::evaluate(const Position& pos) {
 
   bool classical = !Eval::useNNUE
 Value Eval::evaluate(const Position& pos) {
 
   bool classical = !Eval::useNNUE

-                ||  abs(eg_value(pos.psq_score())) >= NNUEThreshold * (16 + pos.rule50_count()) / 16;
+                ||  abs(eg_value(pos.psq_score())) * 16 > NNUEThreshold1 * (16 + pos.rule50_count());

   Value v = classical ? Evaluation<NO_TRACE>(pos).value()
                       : NNUE::evaluate(pos) * 5 / 4 + Tempo;
 
   Value v = classical ? Evaluation<NO_TRACE>(pos).value()
                       : NNUE::evaluate(pos) * 5 / 4 + Tempo;
 

+  if (classical && Eval::useNNUE && abs(v) * 16 < NNUEThreshold2 * (16 + pos.rule50_count()))
+      v = NNUE::evaluate(pos) * 5 / 4 + Tempo;
+

   // Damp down the evaluation linearly when shuffling
   v = v * (100 - pos.rule50_count()) / 100;
 
   // Damp down the evaluation linearly when shuffling
   v = v * (100 - pos.rule50_count()) / 100;