The underlying algorithm is nothing more than `grisu2` that's going to give you roundtrip-able values in the shortest amount of time, the tradeoff is in the 0.05% of numbers that cannot be "encoded" in the shortest possible way.
For a stdlib implementation you may want to use something like `errol4` or `grisu3` plus some other fallback but, as expected, the implementation is slightly more complicated (see [Swift](https://github.com/apple/swift/blob/master/stdlib/public/runtime/SwiftDtoa.cpp) implementation to get a taste).
