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Re: Javascript Math problem

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Stefan Weiss wrote:

> On 2012-04-28 02:30, Michael Haufe (TNO) wrote:
>> Simple enough for the mathematically inclined:
>> 
>> function f(n){ return (n-(n%3))/3 }
> 
> Ah yes, I forgot to add that one. 

However, that approach requires three floating-point operations (and one 
call of a user-defined function), whereas

  Math.floor(n / 3)

only requires two (and one property access and one built-in function call).  
ISTM that therefore the cost and potential rounding error is greater with 
the former than with the latter, and that the latter should be preferred,
at least for n >= 0.

> […]
> In JS, -5.5 % 3 is -2.5 ...

You mean _in conforming implementations of ECMAScript_, of course.

> In PHP, -5.5 % 3 is -2 ...
> 
> In Python, -5.5 % 3 is 0.5 ...
> 
> In Perl, -5.5 % 3 is 1 ...
>   (unless you "use integer", then it depends on the compiler)
> 
> In C, -5.5 % 3 doesn't work at all (int only)...
>   (but fmod(-5.5, 3) returns -2.5)
>   (oh, and the behavior with negative numbers is
>      "implementation defined")

Fascinating.


PointedEars
-- 
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
  -- Richard Cornford, cljs, <f806at$ail$1$8300dec7@news.demon.co.uk>

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Javascript Math problem Tom <thart@vicon.net> - 2012-04-27 15:41 -0700
  Re: Javascript Math problem Stefan Weiss <krewecherl@gmail.com> - 2012-04-28 01:33 +0200
    Re: Javascript Math problem Tom <thart@vicon.net> - 2012-04-27 18:02 -0700
    Re: Javascript Math problem Dr J R Stockton <reply1217@merlyn.demon.co.uk.not.invalid> - 2012-04-29 21:07 +0100
      Re: Javascript Math problem "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-04-30 08:06 +0000
        Re: Javascript Math problem Tom <thart@vicon.net> - 2012-04-30 01:33 -0700
        Re: Javascript Math problem Dr J R Stockton <reply1218@merlyn.demon.co.uk.not.invalid> - 2012-05-01 19:30 +0100
  Re: Javascript Math problem "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2012-04-27 17:30 -0700
    Re: Javascript Math problem Tom <thart@vicon.net> - 2012-04-27 18:05 -0700
    Re: Javascript Math problem Stefan Weiss <krewecherl@gmail.com> - 2012-04-28 04:00 +0200
      Re: Javascript Math problem Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-28 13:04 +0200
        Re: Javascript Math problem Stefan Weiss <krewecherl@gmail.com> - 2012-04-28 21:10 +0200
          Re: Javascript Math problem Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-28 22:23 +0200
            Re: Javascript Math problem "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-04-28 23:39 +0300
            JS/Terminology (was: Javascript Math problem) Stefan Weiss <krewecherl@gmail.com> - 2012-04-29 05:59 +0200
              Re: JS/Terminology Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-29 16:15 +0200
                Re: JS/Terminology Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-29 16:20 +0200
                Re: JS/Terminology Puzzled <scratching.head@example.com> - 2012-05-07 16:22 -0400
                Re: JS/Terminology Gene Wirchenko <genew@ocis.net> - 2012-05-07 14:36 -0700
                Re: JS/Terminology "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-05-08 08:40 +0000
                Re: JS/Terminology Gene Wirchenko <genew@ocis.net> - 2012-05-08 09:29 -0700
            Re: Javascript Math problem John G Harris <john@nospam.demon.co.uk> - 2012-04-29 17:30 +0100
          Re: Javascript Math problem Scott Sauyet <scott.sauyet@gmail.com> - 2012-04-30 06:19 -0700
            Re: Javascript Math problem Dr J R Stockton <reply1218@merlyn.demon.co.uk.not.invalid> - 2012-05-01 19:48 +0100
              Re: Javascript Math problem Gene Wirchenko <genew@ocis.net> - 2012-05-01 19:30 -0700
      Re: Javascript Math problem "Mel Smith" <med_cutout_syntel@aol.com> - 2012-04-28 09:00 -0600
    Re: Javascript Math problem "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-04-28 09:02 +0000

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