Antoine,

> I don't think "register types" matter here. The struct module provides
> interoperability with low-level *data types* (in C and other common
> languages), not CPU *registers*.

OK, see where you're coming from. I guess my thinking was such that struct (and ctypes) support is required for data types that are common within C structures. The fact that 128-bit ints are now appearing within these structures is due to the fact that CPU support has dramatically improved, and are supported natively in register types. So it was kind of an indirect connection.

So the question I guess is whether you think these types are "common enough" in C structs, which for me they certainly are for my data processing applications.. (pretty please :)

> So IMHO the question is whether there is an use case for 128-bit
> integers; *not* for arrays of four 32-bit integers packed in a 128-bit
> register.

Agree completely - just stick to thinking about atomic 128-bit integers. A pack/unpack function should do the conversion, and have nothing to do with this struct support.