Re: Trailing zeros of 100!

From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Subject	Re: Trailing zeros of 100!
Date	2016-01-03 08:57 +1100
Message-ID	<mailman.184.1451771860.11925.python-list@python.org> (permalink)
References	(1 earlier) <CAHzaPEOzP+DZDHOV7s1tDA0AUNhFdBUJKZWCJ5W9F8ec6aH-JA@mail.gmail.com> <mailman.162.1451745109.11925.python-list@python.org> <n68s1t$ke9$1@news.albasani.net> <mailman.172.1451753180.11925.python-list@python.org> <n68vgc$qi6$1@news.albasani.net>

Show all headers | View raw

On Sun, Jan 3, 2016 at 3:56 AM, Robin Koch <robin.koch@t-online.de> wrote:
> Am 02.01.2016 um 17:09 schrieb Tony van der Hoff:
>>
>> On 02/01/16 16:57, Robin Koch wrote:
>>>
>>> sum([int(0.2**k*n) for k in range(1, int(log(n, 5))+1)])
>>
>>
>> But did you actually test it?
>
>
> Yes, should work for n >= 1.
>
> Why do you ask?

Your "should work" does not sound good as a response to "actually
test". Normally I would expect the response to be "Yes, and it worked
for me" (maybe with a log of an interactive session). Floating point
can't represent every integer, and above 2**53 you end up able to
represent only those which are multiples of ever-increasing powers of
two; 100! is between 2**524 and 2**525, so any float operations are
going to be rounding off to the nearest 2**471 or thereabouts.
That's... a lot of rounding. That's like trying to calculate whether
pi is rational, but basing your calculations on the approximation
3.14. :)

ChrisA

Thread

Trailing zeros of 100! katye2007@gmail.com - 2016-01-02 03:49 -0800
  Re: Trailing zeros of 100! David <bouncingcats@gmail.com> - 2016-01-02 23:19 +1100
  Re: Trailing zeros of 100! katye2007@gmail.com - 2016-01-02 04:34 -0800
  Re: Trailing zeros of 100! Vlastimil Brom <vlastimil.brom@gmail.com> - 2016-01-02 13:44 +0100
  Re: Trailing zeros of 100! "yehudak ." <katye2007@gmail.com> - 2016-01-02 15:14 +0200
    Re: Trailing zeros of 100! Robin Koch <robin.koch@t-online.de> - 2016-01-02 16:57 +0100
      Re: Trailing zeros of 100! Tony van der Hoff <tony@vanderhoff.org> - 2016-01-02 17:09 +0100
        Re: Trailing zeros of 100! Robin Koch <robin.koch@t-online.de> - 2016-01-02 17:56 +0100
          Re: Trailing zeros of 100! Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-02 15:24 -0200
          Re: Trailing zeros of 100! Chris Angelico <rosuav@gmail.com> - 2016-01-03 08:57 +1100
            Re: Trailing zeros of 100! Robin Koch <robin.koch@t-online.de> - 2016-01-03 01:02 +0100
              Re: Trailing zeros of 100! Ben Finney <ben+python@benfinney.id.au> - 2016-01-03 11:20 +1100
              Re: Trailing zeros of 100! srinivas devaki <mr.eightnoteight@gmail.com> - 2016-01-03 07:16 +0530
          Re: Trailing zeros of 100! Tony van der Hoff <tony@vanderhoff.org> - 2016-01-03 11:53 +0100
  Re: Trailing zeros of 100! Joel Goldstick <joel.goldstick@gmail.com> - 2016-01-02 09:57 -0500
  Re: Trailing zeros of 100! Vlastimil Brom <vlastimil.brom@gmail.com> - 2016-01-02 16:24 +0100
  Re: Trailing zeros of 100! Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-01-02 15:30 +0000
  Re: Trailing zeros of 100! Robin Koch <robin.koch@t-online.de> - 2016-01-02 16:54 +0100
    Re: Trailing zeros of 100! Peter Otten <__peter__@web.de> - 2016-01-02 18:18 +0100
  Re: Trailing zeros of 100! Tim Chase <python.list@tim.thechases.com> - 2016-01-02 10:33 -0600
  Re: Trailing zeros of 100! "yehudak ." <katye2007@gmail.com> - 2016-01-02 19:34 +0200
  Re: Trailing zeros of 100! Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-01-02 17:44 +0000
    Re: Trailing zeros of 100! Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-03 00:36 +0100
  Re: Trailing zeros of 100! Serhiy Storchaka <storchaka@gmail.com> - 2016-01-02 20:28 +0200
  Re: Trailing zeros of 100! Vlastimil Brom <vlastimil.brom@gmail.com> - 2016-01-02 19:29 +0100
  Re: Trailing zeros of 100! "yehudak ." <katye2007@gmail.com> - 2016-01-02 22:02 +0200
  Re: Trailing zeros of 100! "yehudak ." <katye2007@gmail.com> - 2016-01-02 22:09 +0200
  Re: Trailing zeros of 100! Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-01-02 21:25 +0000
  Re: Trailing zeros of 100! Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-01-02 21:26 +0000

csiph-web