On 03/05/2011 09:52, rusi wrote:
[If you believe it is, then try writing a log(n) fib iteratively :D ]
It took me a while, but this one seems to work:
from collections import namedtuple
Triple = namedtuple('Triple', 'hi mid lo')
Triple.__mul__ = lambda self, other: Triple(
self.hi * other.hi + self.mid * other.mid,
self.hi * other.mid + self.mid * other.lo,
self.mid * other.mid + self.lo * other.lo,
)
def fib(n):
f = Triple(1, 1, 0)
a = Triple(1, 0, 1)
while n:
if n & 1:
a *= f
f *= f
n >>= 1
return a.mid
-- HansM
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