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 rlwidth 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*
## vavgs\* (vec_avg)