Hello Lance,

What compilers do with bit field is not covered by a standard and is implementation defined... so they do just about whatever they want.
BUT, something important is missing in you're code ! If you really want everything to be side by side, bit wise, you have to specify PACKED option on you're structs
search the web :

__attribute__((packed, aligned(X))) 

or

__PACKED__

This will force the compiler to 'pack' all the bits together not waisting anything : so you will have a stable size.

Note : positionning of the inside the struct is implementation defined ... so some compilers put them in on order, and others the other way around
==> you're code won't be very portable