But if sqrt with a double is 27 cycles, then even an L2 lookup is gong to be significantly faster? Am I likely to hit L3 using a 250,000 value lookup table?
Come to think of it actually, the data will be weighted toward the low end of the data, so maybe only putting a table for the first 2/3 of the values would work. That means ifs though, which would probably slow it down even more. Blarg.