AVX512 could define a quarter type since there are three usable types (ignoring suffixes):
so dealing with a vector of ten double elements could be done by
one m512 and one m128 instruction/packet.
Adding a `quarter` typedef would be trivial, but properly using that not so much.
E.g., for a vector of size 14 it might be better to either use two overlapping vectors of size 8, or (with AVX512) mask one vector to size 6.
Also, even without AVX512, there could be use cases for using just one half of a __mm128 packet (for two floats).
If you need this in your own code, you can use the `half` typedef twice.