+ // 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();
+ 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;
+
+ if (pos.is_chess960())
+ v += fix_FRC(pos);