Apart from various nuts and bolts optimizations (eg not using locales, better cache friendless, etc...) it also uses a novel algorithm which is an order of magnitude quicker for many floating points tasks (https://github.com/ulfjack/ryu).
If you actually want to learn about this, then watch the video I linked earlier.
MSFT's one is totally standards compliant and it is a very different beast: https://github.com/microsoft/STL/blob/main/stl/inc/charconv
Apart from various nuts and bolts optimizations (eg not using locales, better cache friendless, etc...) it also uses a novel algorithm which is an order of magnitude quicker for many floating points tasks (https://github.com/ulfjack/ryu).
If you actually want to learn about this, then watch the video I linked earlier.