I'm working on a C version of your program. It was requested that I do a 683 version first. I'm still learning how to get around the hardware limitations of the chip.
Your code is very tight, so it will be hard to match it's performance in C.
I see there will be no time to do any calculation other than a table lookup for the curve. Still, there should be room for two tables in memory. EEPROM will just have to be for saving some other settings.