I'm not the author, but I don't think this amazing little library has gotten the attention it deserves. I saw that the author Sébastien Loisel submitted it to HN about a year ago when he first made it, but it wasn't picked up. So I'm re-submitting. Any detailed questions about the implementation will need to be directed to the author.
Cool stuff. JavaScript wouldn't be my first (or second, or third, or even fifth) choice for numeric work, but I'm sure this will come in handy one day in a project that already exists and just needs a little numerical help.