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: for high PSQ imbalance we use classical,
- // but we switch to NNUE during long shuffling or with high material on the board.
- bool useClassical = !useNNUE ||
- ((pos.count<ALL_PIECES>() > 7)
- && abs(psq) * 5 > (856 + pos.non_pawn_material() / 64) * (10 + pos.rule50_count()));
+ // We use the much less accurate but faster Classical eval when the NNUE
+ // option is set to false. Otherwise we use the NNUE eval unless the
+ // PSQ advantage is decisive and several pieces remain. (~3 Elo)
+ bool useClassical = !useNNUE || (pos.count<ALL_PIECES>() > 7 && abs(psq) > 1760);
if (useClassical)
v = Evaluation<NO_TRACE>(pos).value();
{
int nnueComplexity;
int scale = 1064 + 106 * pos.non_pawn_material() / 5120;
+
+ Color stm = pos.side_to_move();
Value optimism = pos.this_thread()->optimism[stm];
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
+ nnueComplexity = ( 416 * nnueComplexity
+ + 424 * abs(psq - nnue)
+ + (optimism > 0 ? int(optimism) * int(psq - nnue) : 0)
+ ) / 1024;
+
+ // Return hybrid NNUE complexity to caller
+ if (complexity)
*complexity = nnueComplexity;
optimism = optimism * (269 + nnueComplexity) / 256;