Can confirm CPU part. I once tried to replace a 2d stepwise linear function interpolations (basically, a loop finding the right step, then linear interpolation, on a double; the function's objective is to rescale inputs before they become regression's arguments) by LUTs.

All of this looping was happening in another tight loop, and there were multiple LUTs.

It was a failure with overall decreased performance and increased cache misses. Plus, I could never get the same precision.