ned at nedbatchelder.com
Wed Oct 22 17:01:28 CEST 2014
On 10/22/14 5:27 AM, ast wrote:
> "Chris Angelico" <rosuav at gmail.com> a écrit dans le message de
> news:mailman.15058.1413968065.18130.python-list at python.org...
>> On Wed, Oct 22, 2014 at 7:27 PM, ast <nomail at 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:
> 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:
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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