Bitboard ourPawns = pos.pieces(Us, PAWN);
Bitboard theirPawns = pos.pieces(Them, PAWN);
- e->passedPawns[Us] = 0;
+ e->passedPawns[Us] = e->candidatePawns[Us] = 0;
e->kingSquares[Us] = SQ_NONE;
e->semiopenFiles[Us] = 0xFF;
e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
// We now know that there are no friendly pawns beside or behind this
// pawn on adjacent files. We now check whether the pawn is
// backward by looking in the forward direction on the adjacent
- // files, and seeing whether we meet a friendly or an enemy pawn first.
- b = pos.attacks_from<PAWN>(s, Us);
+ // files, and picking the closest pawn there.
+ b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
+ b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
- // Note that we are sure to find something because pawn is not passed
- // nor isolated, so loop is potentially infinite, but it isn't.
- while (!(b & (ourPawns | theirPawns)))
- b = shift_bb<Up>(b);
-
- // The friendly pawn needs to be at least two ranks closer than the
- // enemy pawn in order to help the potentially backward pawn advance.
+ // If we have an enemy pawn in the same or next rank, the pawn is
+ // backward because it cannot advance without being captured.
backward = (b | shift_bb<Up>(b)) & theirPawns;
}
value += ChainMember[f];
if (candidate)
+ {
value += CandidatePassed[relative_rank(Us, s)];
+
+ if (!doubled)
+ e->candidatePawns[Us] |= s;
+ }
}
return value;
for (int f = kf - 1; f <= kf + 1; f++)
{
b = ourPawns & FileBB[f];
- rkUs = b ? relative_rank(Us, lsb(Us, b)) : RANK_1;
+ rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
safety -= ShelterWeakness[rkUs];
b = theirPawns & FileBB[f];
- rkThem = b ? relative_rank(Us, lsb(Us, b)) : RANK_1;
+ rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
}