/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
+ Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
Value Eval::evaluate(const Position& pos) {
Value v;
+ bool useClassical = false;
- // Deciding between classical and NNUE eval: for high PSQ imbalance we use classical,
+ // 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
|| abs(eg_value(pos.psq_score())) * 5 > (850 + pos.non_pawn_material() / 64) * (5 + pos.rule50_count()))
- v = Evaluation<NO_TRACE>(pos).value(); // classical
- else
{
- int scale = 898
- + 24 * pos.count<PAWN>()
- + 33 * pos.non_pawn_material() / 1024;
+ v = Evaluation<NO_TRACE>(pos).value(); // classical
+ useClassical = abs(v) >= 300;
+ }
+ // If result of a classical evaluation is much lower than threshold fall back to NNUE
+ if (useNNUE && !useClassical)
+ {
Value nnue = NNUE::evaluate(pos, true); // NNUE
+ int scale = 1136 + 20 * pos.non_pawn_material() / 1024;
Color stm = pos.side_to_move();
Value optimism = pos.this_thread()->optimism[stm];
+ Value psq = (stm == WHITE ? 1 : -1) * eg_value(pos.psq_score());
+ int complexity = abs(nnue - psq) / 256;
+ optimism *= (1 + complexity);
v = (nnue + optimism) * scale / 1024 - optimism;
if (pos.is_chess960())