From: Colin Bartlett <colinb2r@...>
Date: 2010-07-22T03:49:32+09:00
Subject: Re: How to check if x is a multiple of y

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On Wed, Jul 21, 2010 at 6:45 PM, Robert Klemme
<shortcutter@googlemail.com>wrote:

>  On 21.07.2010 13:20, Xavier Noria wrote:
>
>> On Wednesday, July 21, 2010, Robert Klemme<shortcutter@googlemail.com>
>>  wrote:
>>
>>> ...
>>
>>   I see a benchmark lurking: that version vs. this one.
>>> class Integer
>>>   def multiple_off? number
>>>     zero? || self % number == 0
>>>   end
>>> end
>>>
>>> :-)
>>
>>
>> But that one is not well-defined for 1.multiple_of?(0) :-)
>>
>
> There you see why posting in a hurry is a bad idea.  Thanks for catching
> that.

For what they are worth (which is very little as I distrust benchmarks which
haven't been run sufficiently many times to generate reliable standard
deviations, not to mention my Windows Vista installation doing even more
apparently random and purposeless disk i/o than usual) these benchmarks
suggest that (ignoring the minor bug!) multiple_off? was usually slightly
slower than multiple_of? on my system about two hours ago!

ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-mingw32]
each benchmark is a 1_000_0000.times run;

                    user     system      total        real

 num= 72  denom= 13

multiple_of?    0.921000   0.000000   0.921000 (  1.012000)
multiple_off?   0.967000   0.000000   0.967000 (  1.177000)

multiple_of?    0.827000   0.015000   0.842000 (  0.992000)
multiple_off?   0.983000   0.000000   0.983000 (  1.110000)

 num= 72  denom= 12

multiple_of?    0.874000   0.000000   0.874000 (  1.072000)
multiple_off?   0.967000   0.000000   0.967000 (  1.182000)

multiple_of?    0.936000   0.000000   0.936000 (  1.090000)
multiple_off?   1.030000   0.000000   1.030000 (  1.156000)

 num= 0  denom= 0

multiple_of?    0.874000   0.000000   0.874000 (  1.108000)
multiple_off?   0.780000   0.000000   0.780000 (  1.004000)

multiple_of?    0.827000   0.000000   0.827000 (  1.122000)
multiple_off?   0.889000   0.000000   0.889000 (  1.043000)

 num= 72  denom= 0

multiple_of?   0.905000   0.000000   0.905000 (  1.114000)
multiple_of?   0.936000   0.000000   0.936000 (  1.088000)

multiple_off?
  #<ZeroDivisionError: divided by 0>

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