[robinhouston]

Actually I think that roughly was my point. :-)

You can’t get an exact answer in general by using fixed-size floating-point numbers, as your pseudocode does. The number of bits of precision you need to get an exact answer is going to depend on the input value, presumably linearly.

[kenjackson]

When you round you'll always get the exact integer answer, even using the precision of the golden ratio I gave in the code.

[robinhouston]

That’s really not true. You don’t have to take my word for it: try it with fib(1000), say.

The answer should be:

  43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875

[kenjackson]

Oh, the old n=1000 trick. Well played.