I've created a github repo to hold QEF implementations. The repo currently contains a version created by Leonard Ritter (@paniq) which is a stripped down version of the original implementation by /u/unzret from my previous post. I've also forked that to create an OpenCL version, and added that to the repo too.
These implementations are completely free for any purpose which is an improvement over the reference implementation's license (which was free for non-commercial use). Moreover, this implementation is suitable for use on the GPU which is a technical improvement on the reference version.
I know a lot of people reading this blog are using C# so perhaps someone wants to contribute a C# port? Ideally the repo would be a single resource for QEF code so no one else ever has to write it!