// index[from] is not updated and becomes stale. This works as long as index[]
// is accessed just by known occupied squares.
- Bitboard fromTo = square_bb(from) ^ square_bb(to);
+ Bitboard fromTo = square_bb(from) | square_bb(to);
byTypeBB[ALL_PIECES] ^= fromTo;
byTypeBB[type_of(pc)] ^= fromTo;
byColorBB[color_of(pc)] ^= fromTo;