From my 1980s 8-bit CPU perspective, the instruction is unhinged based solely on the number of letters. Compared to LDA, STA, RTS, that's not an assembler mnemonic, it's a novel. :-)
Incidentally, how is it a GF(2^8) affine transform? As best as I can tell, it’s a GF(2)^8 affine transform, i.e. an affine transform of vectors of bits with normal XOR addition and AND multiplication, and the polynomial defining GF(2^8) just does not enter anywhere. It does enter into GF2P8AFFINEINVQB, but I’m having difficulties finding a geometric description for that one at all.
I believe that the polynomial for GF2P8AFFINEQB is user-defined. One argument is an 8x8 matrix in GF(2) and the result is [A.x + b] in GF(2)^8 for each 8-bit section. Don't quote me on this, but I believe that matrix multiply in GF(2)^8 gets you a transform in GF(2^8).
I think I actually need that instruction and have a use case for it, and it does something with a matrix transpose so I might finally find a real world useful demonstration of a matrix operation I can cite to people who don't know what those mean.
"This is an instruction that doesn't exist in any computer right now, so why should I put it in a machine, if it's supposed to be realistic? Well, it's because it's ahead of time."
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 But all of those needs are rarely in the hot-path, and the FEC algo's are way outdated
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).
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?
Sometimes I read through the instrinsics guide just to play the game of spotting instructions defined primarily because certain cryptologic agencies asked for it.