Alignment of Bit Fields

Whether a bit field can straddle a storage-unit boundary (§3.5.2.1)

Bit fields default to size short, which can cross a byte boundary but not a 16-bit boundary. If the size and location of a bit field would cause it to overflow the current integer, the field is moved to the beginning of the next available integer.

If a bit field is declared as a long, it can hold up to 32 bits.

In either case, an individual field cannot cross a 16- or 32-bit boundary.