Is it fair to say that the main use of extended integers is to "fill the gaps" if the sequence char, short, int, long, long long has missing sizes? Such as if an architecture defines int to be 64-bit and short to be 32-bit, then you could have an extended integer type for 16-bit?
Something like that. The extended integer types were invented by the committee in hopes of a) easing the transition from 16-bit to 32-bit to 64-bit implementations and b) making it possible for implementers targeting new special-purpose hardware to extend the language in useful and hopefully consistent ways to take advantage of the new hardware. One idea was to support bi-endian types in the type system. There was no experience with these types when they were introduced and I don't have the impression they've been as widely adopted as had been envisioned. Intel Bi-endian compiler does provide support for "extended" mixed-endian types in the same program. Martin