The other direction, vec_unpack widening ops, may need some way to tell whether to sign-extend or zero-extend.
-*scalar extsw/b/h gives one set, mv gives another. src elwidth override and dest elwidth override provide the pack/unpack*
+*scalar extsw/b/h gives one set, mv gives another. src elwidth override and dest elwidth override provide the pack/unpack*.
+
+implemented by [[sv/mv.vec]] RM Pack/Unpack mode as long as these instructions
+have that RM Mode.
## vavgs\* (vec_avg)