Square ksq = orient(perspective, pos.square<KING>(perspective));
Bitboard bb = pos.pieces() & ~pos.pieces(KING);
- while (bb) {
- Square s = pop_lsb(&bb);
+ while (bb)
+ {
+ Square s = pop_lsb(bb);
active->push_back(make_index(perspective, s, pos.piece_on(s), ksq));
}
}
- // Get a list of indices for recently changed features
+
+ // AppendChangedIndices() : get a list of indices for recently changed features
+
+ // IMPORTANT: The `pos` in this function is pretty much useless as it
+ // is not always the position the features are updated to. The feature
+ // transformer code right now can update multiple accumulators per move,
+ // but since Stockfish only keeps the full state of the current leaf
+ // search position it is not possible to always pass here the position for
+ // which the accumulator is being updated. Therefore the only thing that
+ // can be reliably extracted from `pos` is the king square for the king
+ // of the `perspective` color (note: not even the other king's square will
+ // match reality in all cases, this is also the reason why `dp` is passed
+ // as a parameter and not extracted from pos.state()). This is of particular
+ // problem for future nets with other feature sets, where updating the active
+ // feature might require more information from the intermediate positions. In
+ // this case the only easy solution is to remove the multiple updates from
+ // the feature transformer update code and only update the accumulator for
+ // the current leaf position (the position after the move).
+
template <Side AssociatedKing>
void HalfKP<AssociatedKing>::AppendChangedIndices(
const Position& pos, const DirtyPiece& dp, Color perspective,