The new release 1.10 is faster (use it) and much more uniformly accurate (accuracy is quite stable throughout function domains, even at the more tricky regions). Yes, faster and more accurate.
The results in comparisons with BigFloat are great!
However, at first the name of the package is a big strange, because in many programming language double is mainly 64 bits, while Double64 in your package is the double of Float64, so it has more decimal numbers than I was expecting.
However, it is a great work! I will note it to use it when I want a more precision than Float64, because clearly it is a lot more performance than BigFloat.
How does it compare now to Multifloats.jl?
Good question. Had not looked.
It is slower by too much. Working on that now,