[LarsKrimi]

It has a fixed polynomial, so not really that useful for anything but AES

The only case where I've had use of GF(2^8) inverses is in FEC algorithms (Forney's algorithm) and then you need some kind of weird polynomial. But all of those needs are rarely in the hot-path, and the FEC algo's are way outdated

[pclmulqdq]

I think the AFFINE and AFFINEINV instructions are specifically for FEC and maybe compression algorithms. I also think they smell like something requested by one of the big customers of Intel (e.g. the government).

[LarsKrimi]

Hmm of course erasure codes would always need to solve these problems. Not sure what modern applications need that in the X86 world

I really think it's only AES since thats the only place I've seen that polynomial used. But of course maybe there's an obscure tape backup FEC algo used somewhere in datacenters?

[Sesse__]

The forward affine matrix is useful for all sorts of bit manipulation, e.g. something as simple as a bit reversal.