double-conversion

I'm the author of Grisu. (http://github.com/google/double-conversion and http://florian.loitsch.com/publications/dtoa-pldi2010.pdf) Grisu is also proven to be always correct. As mentioned in another comment: you have to define "correct". Grisu is always accurate, but may bail out if you need the shortest or closest result. Basically: Grisu will always print a number that reads back to the input. However, it may not be able to print the shortest or closest number (when two decimal outputs have the same shortest length). In that case, it knows this, though, and can tell the user. I would say that the combination of Grisu and Errol is currently the state of the art. Errol is not the fastest, nor is it (afaik) proven to always return the closest result. However, combining Grisu with Errol (as fallback) would probably yield the fastest complet

Author here. Grisu is accurate, but not always optimal. However, it figures out when that happens and lets you bail out to a slower algorithm when that happens. If you want full speed you should use Grisu, and then use Errol as a bailout. A bit more context: there are 3 important properties when printing floating-point numbers. - accurateness: you want the printed number to read back to the same number. - shortness: often you want the shortest decimal representation: "0.3" and not "0.2999999999999999889". The latter is more precise, but reads back to the same number as "0.3". - closeness: given two decimal representations of the same length, you prefer the one that is closer to the actual number. I call the combination of these three properties "optimal". Note that shortness and closeness are not always crucial. For example, a json-encode