Hi Fhub,

In many chess computers, bits are used to indicate if castlings are possible.
When the rook or the king moves, bit change to forbid castling.
In ssystem3|4, bits are used to indicate that king and rooks are at initial positions.
With my patch, you can make a "white little castling" with a black knight in H1, the code does not check the type or color of the piece in H1!!!

Sorry for the workload.

Cordialy.

mychess