Okay, I ported some other simpler C Code from here. Might have been a slight copout, but I didn't want to deal with all the dependencies in the GSL code suggested by Marc, and I don't have much experience with C so it would have been an ordeal. This code tests successfully against wolfram alpha, though, so it may not be too much of a tradeoff.
I put the little file on github, though it's not a go package. Just a simple file that implements the function and has a main routine that tests it.
Here's the link to that. Thanks to Brett Beutell for the help.