// connected_threat() tests whether it is safe to forward prune a move or if
// is somehow connected to the threat move returned by null search.
static bool connected_threat(Position pos, Move m, Move threat)
{
Debug.Assert(Utils.is_ok_M(m));
Debug.Assert(Utils.is_ok_M(threat));
Debug.Assert(!pos.is_capture_or_promotion(m));
Debug.Assert(!pos.is_passed_pawn_push(m));
Square mfrom, mto, tfrom, tto;
mfrom = Utils.from_sq(m);
mto = Utils.to_sq(m);
tfrom = Utils.from_sq(threat);
tto = Utils.to_sq(threat);
// Case 1: Don't prune moves which move the threatened piece
if (mfrom == tto)
return true;
// Case 2: If the threatened piece has value less than or equal to the
// value of the threatening piece, don't prune moves which defend it.
if (pos.is_capture(threat)
&& (Position.PieceValueMidgame[pos.piece_on(tfrom)] >= Position.PieceValueMidgame[pos.piece_on(tto)]
|| Utils.type_of(pos.piece_on(tfrom)) == PieceTypeC.KING)
&& pos.move_attacks_square(m, tto))
return true;
// Case 3: If the moving piece in the threatened move is a slider, don't
// prune safe moves which block its ray.
if (piece_is_slider(pos.piece_on(tfrom))
&& (Utils.bit_is_set(Utils.between_bb(tfrom, tto), mto) != 0)
&& pos.see(m, true) >= 0)
return true;
return false;
}
