From: Tomasz Sobczyk <tomasz.sobczyk1997@gmail.com>
Date: Sat, 12 Jun 2021 18:45:14 +0000 (+0200)
Subject: Reduce the number of accumulator states
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=900f249f596417b35129f1dc357cd5392018e575

Reduce the number of accumulator states

Reduce from 3 to 2. Make the intent of the states clearer.

STC: https://tests.stockfishchess.org/tests/view/60c50111457376eb8bcaad03
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 61888 W: 5007 L: 4944 D: 51937
Ptnml(0-2): 164, 3947, 22649, 4030, 154

LTC: https://tests.stockfishchess.org/tests/view/60c52b1c457376eb8bcaad2c
LLR: 2.94 (-2.94,2.94) <-2.50,0.50>
Total: 20248 W: 688 L: 618 D: 18942
Ptnml(0-2): 7, 551, 8946, 605, 15

closes https://github.com/official-stockfish/Stockfish/pull/3548

No functional change.
---

diff --git a/src/nnue/nnue_accumulator.h b/src/nnue/nnue_accumulator.h
index e24902c4..d41ecf95 100644
--- a/src/nnue/nnue_accumulator.h
+++ b/src/nnue/nnue_accumulator.h
@@ -25,14 +25,11 @@
 
 namespace Stockfish::Eval::NNUE {
 
-  // The accumulator of a StateInfo without parent is set to the INIT state
-  enum AccumulatorState { EMPTY, COMPUTED, INIT };
-
   // Class that holds the result of affine transformation of input features
   struct alignas(CacheLineSize) Accumulator {
     std::int16_t accumulation[2][TransformedFeatureDimensions];
     std::int32_t psqtAccumulation[2][PSQTBuckets];
-    AccumulatorState state[2];
+    bool computed[2];
   };
 
 }  // namespace Stockfish::Eval::NNUE
diff --git a/src/nnue/nnue_feature_transformer.h b/src/nnue/nnue_feature_transformer.h
index ab05f884..59a965ac 100644
--- a/src/nnue/nnue_feature_transformer.h
+++ b/src/nnue/nnue_feature_transformer.h
@@ -383,7 +383,7 @@ namespace Stockfish::Eval::NNUE {
       // of the estimated gain in terms of features to be added/subtracted.
       StateInfo *st = pos.state(), *next = nullptr;
       int gain = FeatureSet::refresh_cost(pos);
-      while (st->accumulator.state[perspective] == EMPTY)
+      while (st->previous && !st->accumulator.computed[perspective])
       {
         // This governs when a full feature refresh is needed and how many
         // updates are better than just one full refresh.
@@ -394,7 +394,7 @@ namespace Stockfish::Eval::NNUE {
         st = st->previous;
       }
 
-      if (st->accumulator.state[perspective] == COMPUTED)
+      if (st->accumulator.computed[perspective])
       {
         if (next == nullptr)
           return;
@@ -412,8 +412,8 @@ namespace Stockfish::Eval::NNUE {
             ksq, st2, perspective, removed[1], added[1]);
 
         // Mark the accumulators as computed.
-        next->accumulator.state[perspective] = COMPUTED;
-        pos.state()->accumulator.state[perspective] = COMPUTED;
+        next->accumulator.computed[perspective] = true;
+        pos.state()->accumulator.computed[perspective] = true;
 
         // Now update the accumulators listed in states_to_update[], where the last element is a sentinel.
         StateInfo *states_to_update[3] =
@@ -533,7 +533,7 @@ namespace Stockfish::Eval::NNUE {
       {
         // Refresh the accumulator
         auto& accumulator = pos.state()->accumulator;
-        accumulator.state[perspective] = COMPUTED;
+        accumulator.computed[perspective] = true;
         IndexList active;
         FeatureSet::append_active_indices(pos, perspective, active);
 
diff --git a/src/position.cpp b/src/position.cpp
index 56cb34e8..ba015d3c 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -282,8 +282,6 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
   chess960 = isChess960;
   thisThread = th;
   set_state(st);
-  st->accumulator.state[WHITE] = Eval::NNUE::INIT;
-  st->accumulator.state[BLACK] = Eval::NNUE::INIT;
 
   assert(pos_is_ok());
 
@@ -704,8 +702,8 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
   ++st->pliesFromNull;
 
   // Used by NNUE
-  st->accumulator.state[WHITE] = Eval::NNUE::EMPTY;
-  st->accumulator.state[BLACK] = Eval::NNUE::EMPTY;
+  st->accumulator.computed[WHITE] = false;
+  st->accumulator.computed[BLACK] = false;
   auto& dp = st->dirtyPiece;
   dp.dirty_num = 1;
 
@@ -1005,8 +1003,8 @@ void Position::do_null_move(StateInfo& newSt) {
 
   st->dirtyPiece.dirty_num = 0;
   st->dirtyPiece.piece[0] = NO_PIECE; // Avoid checks in UpdateAccumulator()
-  st->accumulator.state[WHITE] = Eval::NNUE::EMPTY;
-  st->accumulator.state[BLACK] = Eval::NNUE::EMPTY;
+  st->accumulator.computed[WHITE] = false;
+  st->accumulator.computed[BLACK] = false;
 
   if (st->epSquare != SQ_NONE)
   {