Yet another Fibonacci mini-challenge (HP-42S/Free42)

[Thomas Okken]

NOT +/-

That's actually three bytes, not two, but 1 BASE+ is four bytes, so it does save one byte.

Anyway, now I see why this cleverness causes this implementation to fail for n > 50: that's where the BASE functions' 36-bit arithmetic goes out of range. You do need to use IP if you want to avoid that limitation.