A quick search shows that this snippet, including comments, is included in thousands of Github repos [1], so it's not surprising that the model learned to reproduce it verbatim.

It's such a famous snippet that it's even included in full on Wikipedia [2].

I wouldn't be surprised if the next version of Copilot filtered these out.

[1] https://github.com/search?q=0x5f3759df+what+the+fuck&type=co...

[2] https://en.wikipedia.org/wiki/Fast_inverse_square_root#Overv...