alt Hacker NewsNice, but it's too late I needed a different API for future use in my custom sprintf so I made mulle-dtostr (https://github.com/mulle-core/mulle-dtostr). On my machine (AMD) that benchmarked in a quick try quite a bit faster even, but I was just checking that it didn't regress too badly and didn't look at it closer.
Please note that there is some error in your port:
Error: roundtrip fail 4.9406564584124654e-324 -> '5.e-309' -> 4.9999999999999995e-309
Error: roundtrip fail 6.6302941479442929e-310 -> '6.6302941479443e-309' -> 6.6302941479442979e-309
Error: roundtrip fail -1.9153028533493997e-310 -> '-1.9153028533494e-309' -> -1.9153028533493997e-309
Error: roundtrip fail -2.5783653320086361e-312 -> '-2.57836533201e-309' -> -2.5783653320099997e-309