Square ksq = pos.king_square(Us);
// Penalize rooks which are trapped inside a king. Penalize more if
- // king has lost right to castle.
+ // king has lost castling availability.
if ( ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))
&& (rank_of(ksq) == rank_of(s) || relative_rank(Us, ksq) == RANK_1)
&& !ei.pi->semiopen_on_side(Us, file_of(ksq), file_of(ksq) < FILE_E))