The code I've written and still working on is using Eigen, which TensorFlow also uses for its matrix operations, so, I'm not far off from these guys in terms of speed, if not ahead.

The code I've written can complete 1.7 million evaluations per core, per second, on older hardware, which is used to evaluate things up to 1e-6 accuracy, which pretty neat for what I'm working on.

[0]: https://eigen.tuxfamily.org/index.php?title=Main_Page