Fastest C++ way to convert float to string

I have encountered problem of converting float to string where to_string is too slow for me as my data might involves few millions floats.

I already have solution on how to write those data out fast, thanks to peter.write text file fast

However, after solving that problem, i soon realized that the conversion of float to string is leaving a big impact.

So, is there any ideas or solution for this other than using other non standard library??