v = Evaluation<NO_TRACE>(pos).value();
else
{
- // scale and shift NNUE for compatibility with search and classical evaluation
+ // Scale and shift NNUE for compatibility with search and classical evaluation
auto adjusted_NNUE = [&](){ return NNUE::evaluate(pos) * 5 / 4 + Tempo; };
- // if there is PSQ imbalance use classical eval, with small probability if it is small
+ // If there is PSQ imbalance use classical eval, with small probability if it is small
Value psq = Value(abs(eg_value(pos.psq_score())));
int r50 = 16 + pos.rule50_count();
bool largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
v = classical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();
- // if the classical eval is small and imbalance large, use NNUE nevertheless.
+ // If the classical eval is small and imbalance large, use NNUE nevertheless.
+ // For the case of opposite colored bishops, switch to NNUE eval with
+ // small probability if the classical eval is less than the threshold.
if ( largePsq
- && abs(v) * 16 < NNUEThreshold2 * r50)
+ && (abs(v) * 16 < NNUEThreshold2 * r50
+ || ( pos.opposite_bishops()
+ && abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50
+ && !(pos.this_thread()->nodes & 0xB))))
v = adjusted_NNUE();
}