We also have Base.TwicePrecision (nicer in 0.7 than it is in 0.6). Although using that could conceivably be a bit fraught because it’s the engine that underlies the ability of ranges to hit their endpoints exactly, and so there are a few methods that dispatch specially.
My experience in other packages leads me to think that binary dependencies are to be avoided wherever possible. For a huge C library it might be worth it because it wouldn’t be easy to replicate, but in this case we already have credible pure-Julia implementations.