From: Tomasz Sobczyk <tomasz.sobczyk1997@gmail.com>
Date: Tue, 25 May 2021 11:09:40 +0000 (+0200)
Subject: Expose the lazy threshold for the feature transformer PSQT as a parameter.
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=9d53129075177cb11b63b43236556051ba60f7dd

Expose the lazy threshold for the feature transformer PSQT as a parameter.

Definition of the lazy threshold moved to evaluate.cpp where all others are.
Lazy threshold only used for real searches, not used for the "eval" call.
This preserves the purity of NNUE evaluation, which is useful to verify
consistency between the engine and the NNUE trainer.

closes https://github.com/official-stockfish/Stockfish/pull/3499

No functional change
---

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index c8094ca8..04d41d5f 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -214,11 +214,12 @@ using namespace Trace;
 namespace {
 
   // Threshold for lazy and space evaluation
-  constexpr Value LazyThreshold1 =  Value(1565);
-  constexpr Value LazyThreshold2 =  Value(1102);
-  constexpr Value SpaceThreshold = Value(11551);
-  constexpr Value NNUEThreshold1 =   Value(682);
-  constexpr Value NNUEThreshold2 =   Value(176);
+  constexpr Value LazyThreshold1    =  Value(1565);
+  constexpr Value LazyThreshold2    =  Value(1102);
+  constexpr Value LazyThresholdNNUE =  Value(1400);
+  constexpr Value SpaceThreshold    = Value(11551);
+  constexpr Value NNUEThreshold1    =   Value(682);
+  constexpr Value NNUEThreshold2    =   Value(176);
 
   // KingAttackWeights[PieceType] contains king attack weights by piece type
   constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
@@ -1119,7 +1120,7 @@ Value Eval::evaluate(const Position& pos) {
 
          int scale = 903 + 28 * pos.count<PAWN>() + 28 * pos.non_pawn_material() / 1024;
 
-         Value nnue = NNUE::evaluate(pos, true) * scale / 1024;
+         Value nnue = NNUE::evaluate(pos, true, LazyThresholdNNUE) * scale / 1024;
 
          if (pos.is_chess960())
              nnue += fix_FRC(pos);
diff --git a/src/evaluate.h b/src/evaluate.h
index 41aace67..6bc1f0b3 100644
--- a/src/evaluate.h
+++ b/src/evaluate.h
@@ -43,7 +43,7 @@ namespace Eval {
 
   namespace NNUE {
 
-    Value evaluate(const Position& pos, bool adjusted = false);
+    Value evaluate(const Position& pos, bool adjusted = false, Value lazyThreshold = VALUE_INFINITE);
     bool load_eval(std::string name, std::istream& stream);
     bool save_eval(std::ostream& stream);
     void init();
diff --git a/src/nnue/evaluate_nnue.cpp b/src/nnue/evaluate_nnue.cpp
index cee77fe9..99711cd5 100644
--- a/src/nnue/evaluate_nnue.cpp
+++ b/src/nnue/evaluate_nnue.cpp
@@ -134,7 +134,7 @@ namespace Stockfish::Eval::NNUE {
   }
 
   // Evaluation function. Perform differential calculation.
-  Value evaluate(const Position& pos, bool adjusted) {
+  Value evaluate(const Position& pos, bool adjusted, Value lazyThreshold) {
 
     // We manually align the arrays on the stack because with gcc < 9.3
     // overaligning stack variables with alignas() doesn't work correctly.
@@ -158,7 +158,7 @@ namespace Stockfish::Eval::NNUE {
     ASSERT_ALIGNED(buffer, alignment);
 
     const std::size_t bucket = (pos.count<ALL_PIECES>() - 1) / 4;
-    const auto [psqt, lazy] = featureTransformer->transform(pos, transformedFeatures, bucket);
+    const auto [psqt, lazy] = featureTransformer->transform(pos, transformedFeatures, bucket, lazyThreshold);
 
     if (lazy)
       return static_cast<Value>(psqt / OutputScale);
diff --git a/src/nnue/nnue_feature_transformer.h b/src/nnue/nnue_feature_transformer.h
index bfa2e25a..e81f54fa 100644
--- a/src/nnue/nnue_feature_transformer.h
+++ b/src/nnue/nnue_feature_transformer.h
@@ -124,8 +124,6 @@ namespace Stockfish::Eval::NNUE {
     // Number of output dimensions for one side
     static constexpr IndexType HalfDimensions = TransformedFeatureDimensions;
 
-    static constexpr int LazyThreshold = 1400;
-
     #ifdef VECTOR
     static constexpr IndexType TileHeight = NumRegs * sizeof(vec_t) / 2;
     static constexpr IndexType PsqtTileHeight = NumPsqtRegs * sizeof(psqt_vec_t) / 4;
@@ -171,7 +169,7 @@ namespace Stockfish::Eval::NNUE {
     }
 
     // Convert input features
-    std::pair<std::int32_t, bool> transform(const Position& pos, OutputType* output, int bucket) const {
+    std::pair<std::int32_t, bool> transform(const Position& pos, OutputType* output, int bucket, Value lazyThreshold) const {
       update_accumulator(pos, WHITE);
       update_accumulator(pos, BLACK);
 
@@ -184,7 +182,7 @@ namespace Stockfish::Eval::NNUE {
           - psqtAccumulation[static_cast<int>(perspectives[1])][bucket]
         ) / 2;
 
-      if (abs(psqt) > LazyThreshold * OutputScale)
+      if (abs(psqt) > (int)lazyThreshold * OutputScale)
         return { psqt, true };
 
   #if defined(USE_AVX512)