Re: (-1)**1000

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Date	Wed, 22 Oct 2014 19:54:16 +1100
Subject	Re: (-1)**1000
From	Chris Angelico <rosuav@gmail.com>
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On Wed, Oct 22, 2014 at 7:27 PM, ast <nomail@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. Any modern programming language on any modern
CPU architecture should be able to handle this kind of thing. But even
the naive approach is likely to be fast enough.

>>> x=1
>>> for i in range(1000000): x*=-1

I had to go as far as a million iterations before this, implemented
purely in Python with absolutely no optimization, demonstrated a
visible pause (of about a quarter second) on my not-exactly-new
Windows laptop. My Linux desktop, with a rather hotter CPU, has no
trouble with a million, so I'd have to go higher to get a pause out of
it.

And actually, about half of that time is spent in the loop - replacing
the assignment with "pass" still leaves half the iteration time.

Poor performance is a crime. Python is innocent until proven guilty.
And the burden of proof is seldom met.

ChrisA

Thread

(-1)**1000 "ast" <nomail@invalid.com> - 2014-10-22 10:27 +0200
  Re: (-1)**1000 Chris Angelico <rosuav@gmail.com> - 2014-10-22 19:54 +1100
    Re: (-1)**1000 "ast" <nomail@invalid.com> - 2014-10-22 11:27 +0200
      Re: (-1)**1000 Peter Otten <__peter__@web.de> - 2014-10-22 12:29 +0200
      Re: (-1)**1000 Michiel Overtoom <motoom@xs4all.nl> - 2014-10-22 12:38 +0200
      Re: (-1)**1000 Tim Chase <python.list@tim.thechases.com> - 2014-10-22 05:43 -0500
      Re: (-1)**1000 Peter Otten <__peter__@web.de> - 2014-10-22 13:02 +0200
      Re: (-1)**1000 Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-22 08:23 -0600
      Re: (-1)**1000 Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-22 08:29 -0600
      Re: (-1)**1000 Ned Batchelder <ned@nedbatchelder.com> - 2014-10-22 11:01 -0400
    Re: (-1)**1000 wxjmfauth@gmail.com - 2014-10-22 04:35 -0700
  Re: (-1)**1000 Peter Otten <__peter__@web.de> - 2014-10-22 11:13 +0200
  Re: (-1)**1000 Terry Reedy <tjreedy@udel.edu> - 2014-10-22 13:15 -0400
  Re: (-1)**1000 Dave Angel <davea@davea.name> - 2014-10-24 13:57 -0400
  Re: (-1)**1000 Tony the Tiger <tony@tiger.invalid> - 2014-10-26 20:07 +0000
    Re: (-1)**1000 Ned Batchelder <ned@nedbatchelder.com> - 2014-10-26 16:45 -0400
    Re: (-1)**1000 Stefan Behnel <stefan_ml@behnel.de> - 2014-10-29 20:31 +0100

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