OK, I upgraded the patch, including style adjustments to GNU style despite feeling that not having clang-format support for GNU style leads to it driving away contributors. It also credits Andy, and I have personally e-mailed Andy before.

I think the code is using https://en.wikipedia.org/wiki/Estrin%27s_scheme but I have no scholarship applying this to AES-GCM. I will have to look closer.

I think I am doing to try to do this on top of the work of Szabolcs Nagy[1] with the goal of making it portable, and also serving as a test cast to my carry-less multiplication intrinsic RFC[2]. Hopefully I can also remove the manual register allocation that makes it still a derivitive work of Andy, however this algorithm takes advantage of the communicative properties of carry-less multiplication, which is mult(H) on page 5 of the gcm spec[3], this communicative property works differently than with addition and multiplication in a way I do not entirely understand.

I don't see it as a priority right now. We should keep it in mind for T3811 .