Sadly there are legal issues with the original implementation, as has already been noticed by the Scikit-Learn maintainers [1]. =( I am speaking partially out of personal experience since this is a reason why I have not actually read the original source code, waiting either for a free implementation to appear or enough spare time to spin one myself.
[1]: https://github.com/scikit-learn/scikit-learn/pull/4025#discu...