#undef S
+ // Threats weights indexed by sente (side to move has a bigger weight)
+ const int ConcurrentThreatsWeight[2] = { 3, 15 };
+ const int ThreatsWeight[2] = { 249, 267 };
+
// Bonus for unstoppable passed pawns
const Value UnstoppablePawnValue = Value(0x500);
const Color Them = (Us == WHITE ? BLACK : WHITE);
Bitboard b;
+ Value mg, eg;
+ int sente, threatCount = 0;
Score bonus = make_score(0, 0);
// Enemy pieces not defended by a pawn and under our attack
if (b)
for (PieceType pt2 = PAWN; pt2 < KING; pt2++)
if (b & pos.pieces(pt2))
+ {
bonus += ThreatBonus[pt1][pt2];
+ threatCount++;
+ }
}
- ei.value += Sign[Us] * bonus;
+
+ sente = (Us == pos.side_to_move());
+
+ // Non linear threat evaluation. Increase threats score according to the
+ // number of concurrent threats and to the side to move.
+ mg = (mg_value(bonus) + mg_value(bonus) * ConcurrentThreatsWeight[sente] * threatCount / 256) * ThreatsWeight[sente] / 256;
+ eg = (eg_value(bonus) + eg_value(bonus) * ConcurrentThreatsWeight[sente] * threatCount / 256) * ThreatsWeight[sente] / 256;
+
+ ei.value += Sign[Us] * make_score(mg, eg);
}