Use NNUE complexity in search, retune related parameters

This builds on ideas of xoto10 and mstembera to use more output from NNUE in the search algorithm.

passed STC:
https://tests.stockfishchess.org/tests/view/62ae454fe7ee5525ef88a957
LLR: 2.95 (-2.94,2.94) <0.00,2.50>
Total: 89208 W: 24127 L: 23753 D: 41328
Ptnml(0-2): 400, 9886, 23642, 10292, 384

passed LTC:
https://tests.stockfishchess.org/tests/view/62acc6ddd89eb6cf1e0750a1
LLR: 2.93 (-2.94,2.94) <0.50,3.00>
Total: 56352 W: 15430 L: 15115 D: 25807
Ptnml(0-2): 44, 5501, 16782, 5794, 55

closes https://github.com/official-stockfish/Stockfish/pull/4088

bench 5332964

src/evaluate.cpp

@@ -1080,35 +1080,39 @@ 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) {
+Value Eval::evaluate(const Position& pos, int* complexity) {
 
   Value v;
+  Color stm = pos.side_to_move();
+  Value psq = pos.psq_eg_stm();
   // Deciding between classical and NNUE eval (~10 Elo): for high PSQ imbalance we use classical,
   // but we switch to NNUE during long shuffling or with high material on the board.
-  bool useClassical = (pos.this_thread()->depth > 9 || pos.count<ALL_PIECES>() > 7) &&
-          abs(eg_value(pos.psq_score())) * 5 > (856 + pos.non_pawn_material() / 64) * (10 + pos.rule50_count());
+  bool useClassical =    (pos.this_thread()->depth > 9 || pos.count<ALL_PIECES>() > 7)
+                      && abs(psq) * 5 > (856 + pos.non_pawn_material() / 64) * (10 + pos.rule50_count());
 
   // Deciding between classical and NNUE eval (~10 Elo): for high PSQ imbalance we use classical,
   // but we switch to NNUE during long shuffling or with high material on the board.
   if (!useNNUE || useClassical)
   {
-      v = Evaluation<NO_TRACE>(pos).value();          // classical
+      v = Evaluation<NO_TRACE>(pos).value();
       useClassical = abs(v) >= 297;
   }
 
   // If result of a classical evaluation is much lower than threshold fall back to NNUE
   if (useNNUE && !useClassical)
   {
-       int complexity;
-       int scale      = 1048 + 109 * pos.non_pawn_material() / 5120;
-       Color stm      = pos.side_to_move();
+       int nnueComplexity;
+       int scale = 1092 + 106 * pos.non_pawn_material() / 5120;
        Value optimism = pos.this_thread()->optimism[stm];
-       Value psq      = (stm == WHITE ? 1 : -1) * eg_value(pos.psq_score());
-       Value nnue     = NNUE::evaluate(pos, true, &complexity);     // NNUE
 
-       complexity = (137 * complexity + 137 * abs(nnue - psq)) / 256;
-       optimism = optimism * (255 + complexity) / 256;
-       v = (nnue * scale + optimism * (scale - 848)) / 1024;
+       Value nnue = NNUE::evaluate(pos, true, &nnueComplexity);
+       // Blend nnue complexity with (semi)classical complexity
+       nnueComplexity = (104 * nnueComplexity + 131 * abs(nnue - psq)) / 256;
+       if (complexity) // Return hybrid NNUE complexity to caller
+           *complexity = nnueComplexity;
+
+       optimism = optimism * (269 + nnueComplexity) / 256;
+       v = (nnue * scale + optimism * (scale - 754)) / 1024;
 
        if (pos.is_chess960())
            v += fix_FRC(pos);
@@ -1120,6 +1124,10 @@ Value Eval::evaluate(const Position& pos) {
   // 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 && (!useNNUE || useClassical))
+       *complexity = abs(v - psq);
+
   return v;
 }
 

src/evaluate.h

@@ -31,7 +31,7 @@ class Position;
 namespace Eval {
 
   std::string trace(Position& pos);
-  Value evaluate(const Position& pos);
+  Value evaluate(const Position& pos, int* complexity = nullptr);
 
   extern bool useNNUE;
   extern std::string currentEvalFileName;

src/nnue/evaluate_nnue.cpp

@@ -143,7 +143,7 @@ namespace Stockfish::Eval::NNUE {
     // overaligning stack variables with alignas() doesn't work correctly.
 
     constexpr uint64_t alignment = CacheLineSize;
-    int delta = 10 - pos.non_pawn_material() / 1515;
+    int delta = 24 - pos.non_pawn_material() / 9560;
 
 #if defined(ALIGNAS_ON_STACK_VARIABLES_BROKEN)
     TransformedFeatureType transformedFeaturesUnaligned[
@@ -166,7 +166,7 @@ namespace Stockfish::Eval::NNUE {
 
     // Give more value to positional evaluation when adjusted flag is set
     if (adjusted)
-        return static_cast<Value>(((128 - delta) * psqt + (128 + delta) * positional) / (128 * OutputScale));
+        return static_cast<Value>(((1024 - delta) * psqt + (1024 + delta) * positional) / (1024 * OutputScale));
     else
         return static_cast<Value>((psqt + positional) / OutputScale);
   }

src/position.h

@@ -161,6 +161,7 @@ public:
   bool has_repeated() const;
   int rule50_count() const;
   Score psq_score() const;
+  Value psq_eg_stm() const;
   Value non_pawn_material(Color c) const;
   Value non_pawn_material() const;
 
@@ -342,6 +343,10 @@ inline Score Position::psq_score() const {
   return psq;
 }
 
+inline Value Position::psq_eg_stm() const {
+  return (sideToMove == WHITE ? 1 : -1) * eg_value(psq);
+}
+
 inline Value Position::non_pawn_material(Color c) const {
   return st->nonPawnMaterial[c];
 }

src/search.cpp

@@ -307,7 +307,7 @@ void Thread::search() {
 
   multiPV = std::min(multiPV, rootMoves.size());
 
-  complexityAverage.set(202, 1);
+  complexityAverage.set(174, 1);
 
   trend         = SCORE_ZERO;
   optimism[ us] = Value(39);
@@ -472,7 +472,7 @@ void Thread::search() {
           double reduction = (1.56 + mainThread->previousTimeReduction) / (2.20 * timeReduction);
           double bestMoveInstability = 1 + 1.7 * totBestMoveChanges / Threads.size();
           int complexity = mainThread->complexityAverage.value();
-          double complexPosition = std::clamp(1.0 + (complexity - 326) / 1618.1, 0.5, 1.5);
+          double complexPosition = std::clamp(1.0 + (complexity - 277) / 1819, 0.5, 1.5);
 
           double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition;
 
@@ -736,7 +736,9 @@ namespace {
         // Never assume anything about values stored in TT
         ss->staticEval = eval = tte->eval();
         if (eval == VALUE_NONE)
-            ss->staticEval = eval = evaluate(pos);
+            ss->staticEval = eval = evaluate(pos, &complexity);
+        else // Fall back to (semi)classical complexity for TT hits, the NNUE complexity is lost
+            complexity = abs(ss->staticEval - pos.psq_eg_stm());
 
         // Randomize draw evaluation
         if (eval == VALUE_DRAW)
@@ -749,13 +751,15 @@ namespace {
     }
     else
     {
-        ss->staticEval = eval = evaluate(pos);
+        ss->staticEval = eval = evaluate(pos, &complexity);
 
         // Save static evaluation into transposition table
         if (!excludedMove)
             tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
     }
 
+    thisThread->complexityAverage.update(complexity);
+
     // Use static evaluation difference to improve quiet move ordering (~3 Elo)
     if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
     {
@@ -770,11 +774,7 @@ namespace {
     improvement =   (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
                   : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
                   :                                    175;
-
     improving = improvement > 0;
-    complexity = abs(ss->staticEval - (us == WHITE ? eg_value(pos.psq_score()) : -eg_value(pos.psq_score())));
-
-    thisThread->complexityAverage.update(complexity);
 
     // Step 7. Razoring.
     // If eval is really low check with qsearch if it can exceed alpha, if it can't,
@@ -803,7 +803,7 @@ namespace {
         && (ss-1)->statScore < 14695
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 15 * depth - improvement / 15 + 198 + complexity / 28
+        &&  ss->staticEval >= beta - 15 * depth - improvement / 15 + 201 + complexity / 24
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -811,7 +811,7 @@ namespace {
         assert(eval - beta >= 0);
 
         // Null move dynamic reduction based on depth, eval and complexity of position
-        Depth R = std::min(int(eval - beta) / 147, 5) + depth / 3 + 4 - (complexity > 753);
+        Depth R = std::min(int(eval - beta) / 147, 5) + depth / 3 + 4 - (complexity > 650);
 
         ss->currentMove = MOVE_NULL;
         ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];