Have you commented without looking at the link?

> Because this is a matrix multiplication operation fundamentally, the order is O(n^2) or so in terms of scaling. Sooooo yeah, quadratically difficult to calculate as the data per block grows.

It's literally in repo's description -

  Reed-Solomon coder computing one million parity
  blocks at 1 GB/s. O(N*log(N)) algo employing FFT.

That's what makes FastECC notable. The repo is 5 years old. Obviously, it's going to be more than 1.2 GB/s on a modern hardware.