Faster Recursive Fibonacci Numbers

[Steven D'Aprano]

On Fri, 20 May 2011 16:54:06 +1000, Chris Angelico wrote:

> If someone has time to kill (as if!), it'd be awesome to get a new
> numeric type that uses bc's code; any other numeric type (int, long,
> float) could autopromote to it, removing the dilemma of which to promote
> out of long and float. Hmm... Python 4.0, 'bc' is the new default
> integer and everything else is a performance optimization? Heh.

The problem is, it isn't *just* a performance optimization, there is a 
semantic difference too. Consider:

>>> x = 1e-300
>>> x*x == 0
True

But using something with more precision:

>>> from fractions import Fraction
>>> x = Fraction(10)**-300
>>> x*x == 0
False


So you get different behaviour between floats and arbitrary precision 
numbers.



-- 
Steven