On 10/22/14 5:27 AM, ast wrote:
"Chris Angelico" <ros...@gmail.com> a écrit dans le message de
news:mailman.15058.1413968065.18130.python-l...@python.org...
On Wed, Oct 22, 2014 at 7:27 PM, ast <nom...@invalid.com> wrote:
If i am writing (-1)**1000 on a python program, will the
interpreter do (-1)*(-1)*...*(-1) or something clever ?
In fact i have (-1)**N with N an integer potentially big.
Exponentiation is far more efficient than the naive implementation of
iterated multiplication.
In the very particular case of (-1)**N, I belive that Python check
the odd or even parity of N and provides the result accordingly.
I tried:
(-1)**1000000000000000000000000000000000
1
(-1)**1000000000000000000000000000000001
-1
and it is instantaneous
Keep in mind that actually calculating the exponentiation wouldn't do
1000000000000000000000000000000000 multiplications anyway: the clever
way to do integer powers is by squaring based on the binary
representation of the exponent. It's explained here:
http://stackoverflow.com/a/101613/14343
So even if Python is actually calculating the value, it's only doing 75
multiplications or so.
--
Ned Batchelder, http://nedbatchelder.com
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