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Re: Date arithmetic

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From Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups comp.lang.javascript
Subject Re: Date arithmetic
Date Mon, 17 Nov 2014 00:52:45 +0100
Organization PointedEars Software (PES)
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Dr J R Stockton wrote:

> […] Christoph M. Becker wrote:
>> Dr J R Stockton wrote:
>> > […] Christoph M. Becker posted:
>> >> The calculation in jsx.date.dateOfYear() is rather intriguing; I
>> >> wasn't aware of that formula.
>> > 
>> > What formula?
>> 
>> The formula to calculate the day of the year for days between march and
>> december that is used in jsx.date.dateOfYear()[1]:
>> 
>>   Math.floor(30.6 * (month + 1) - 91.4) + dayOfMonth
>>   + (jsx.date.isLeapYear(date.getFullYear()) ? 60 : 59);
>> 
>> [1] <http://pointedears.de/wsvn/JSX/trunk/date.js>
> 
> You mean days between February and January in that order.

No, he means what he wrote, and, with the exception of the use of “between” 
(which should be “from”, and month names are always capitalized), I concur.  
The numbers of the days in January are covered by Date.prototype.getDate(), 
and the numbers of the days in February by addition of 31, the number of 
days in every January.  The formula is only the last part of the approach.

> Unsubtle.  The first part of the expression seems derived from, but does
> not take full benefit from, Zeller's Congruence

Interesting.  If it has not already happened and proves to be correct, this 
information should be added as reference to the Wikipedia article I took the 
approach from.

> [I believe Zeller to have been a non-concurrent compatriot of yours (and
> that his children's marriages had an uncommon property)].

Figures; you concern yourself too much with the people, their ancestry, 
relationships and descendants, and too little with the topic of the 
discussion:

> My website has [I think all of] Zeller's relevant papers in the original
> and in English translation.  By considering Zeller to the full, one easily
> enough gets an expression for the daycount from an Epoch.

(Interesting, too, although not applicable here.)

> But we know that Swifty wants to process his _hand-entered_ dates.
> A quick test in current Firefox on an elderly PC shows that it executes a
> million of 'new Date()' in about 2.2 seconds.  So there can be no
> perceptible advantage in doing anything other than 'new Date()' on each
> input, subtracting, dividing by 864e5, and rounding to integer, to get
> Swifty his date difference.

You are missing the point and are preaching to the choir.  It has already 
been stated twice (at least) in this thread that for this use-case the 
approach in jsx.date.getDayOfYear() is not the most efficient one, and that 
the division approach is probably the best one.  After all, it was Christoph 
who suggested it first, in this thread at least.
 
-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | SVN: <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | ES Matrix: <http://PointedEars.de/es-matrix>
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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Thread

Date arithmetic Swifty <steve.j.swift@gmail.com> - 2014-11-11 12:38 +0000
  Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-11-11 15:10 +0100
    Re: Date arithmetic Swifty <steve.j.swift@gmail.com> - 2014-11-11 22:07 +0000
      Re: Date arithmetic Tim Streater <timstreater@greenbee.net> - 2014-11-11 22:37 +0000
        Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-12 02:40 +0100
          Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-11-12 08:21 +0100
            Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-13 15:27 +0100
              Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 21:26 +0100
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-14 14:16 +0100
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-15 07:13 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-15 19:36 +0000
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-16 17:24 +0100
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-16 18:49 +0100
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-17 00:14 +0100
                Re: Date arithmetic Dr J R Stockton <J.R.Stockton@physics.org> - 2014-11-16 10:51 -0800
                Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-11-16 20:17 +0100
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-17 00:52 +0100
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-17 01:11 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-18 16:18 +0000
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-19 11:00 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-21 22:58 +0000
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-22 18:33 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-23 19:38 +0000
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-24 01:14 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-25 21:17 +0000
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-26 18:25 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-27 19:34 +0000
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-28 01:25 +0100
                Re: Date arithmetic Dr J R Stockton <J.R.Stockton@physics.org> - 2014-11-28 05:29 -0800
                Re: Date arithmetic Andrew Poulos <ap_prog@hotmail.com> - 2014-11-28 11:44 +1100
                Re: Date arithmetic Dr J R Stockton <J.R.Stockton@physics.org> - 2014-11-28 04:52 -0800
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-28 14:24 +0100
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-28 14:47 +0100
                Re: Date arithmetic Dr J R Stockton <J.R.Stockton@physics.org> - 2014-11-28 06:12 -0800
                Re: Date arithmetic Andrew Poulos <ap_prog@hotmail.com> - 2014-11-29 16:59 +1100
                Re: Date arithmetic John Harris <niam@jghnorth.org.uk.invalid> - 2014-11-29 20:05 +0000
                Re: Date arithmetic Joao Rodrigues <groups_jr-1@yahoo.com> - 2014-11-29 23:47 -0200
                Re: Date arithmetic Andrew Poulos <ap_prog@hotmail.com> - 2014-12-01 10:44 +1100
                Re: Date arithmetic Tim Streater <timstreater@greenbee.net> - 2014-11-30 23:54 +0000
                Re: Date arithmetic Andrew Poulos <ap_prog@hotmail.com> - 2014-12-01 13:01 +1100
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-17 01:34 +0100
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-17 01:41 +0100
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-18 19:06 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-18 16:26 +0000
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-19 17:52 +0100
                Re: Date arithmetic Gene Wirchenko <genew@telus.net> - 2014-11-19 09:44 -0800
                Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-11-19 19:34 +0100
                Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-19 19:13 +0000
                Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-11-19 22:18 +0100
                Re: Date arithmetic Gene Wirchenko <genew@telus.net> - 2014-11-19 13:43 -0800
                Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-19 22:40 +0000
                Re: Date arithmetic Tim Streater <timstreater@greenbee.net> - 2014-11-19 22:51 +0000
                Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-19 23:35 +0000
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-19 23:10 +0100
                Re: Date arithmetic Tim Streater <timstreater@greenbee.net> - 2014-11-19 22:32 +0000
                Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-19 23:26 +0000
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-20 00:47 +0100
                Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-20 00:17 +0000
                Re: Date arithmetic Dr J R Stockton <J.R.Stockton@physics.org> - 2014-11-20 01:18 -0800
                Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-20 13:47 +0000
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-21 22:29 +0000
                Re: Date arithmetic Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2014-11-19 19:24 -0200
                Re: Date arithmetic Gene Wirchenko <genew@telus.net> - 2014-11-19 13:40 -0800
                Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-19 23:40 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-18 16:44 +0000
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-19 11:20 +0100
                Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-14 20:45 +0000
                Re: Date arithmetic "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2014-11-15 14:13 -0800
                Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-15 23:42 +0100
      Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-11-12 00:23 +0100
      Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-12 13:24 +0000
        Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-12 14:43 +0100
          Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-12 19:48 +0100
            Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-13 01:18 +0100
          Re: Date arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-12 20:19 +0000
            Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-13 03:42 +0100
    Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-12 20:06 +0000
    Re: Date arithmetic RobG <rgqld@iinet.net.au> - 2014-11-23 20:51 -0800
      Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-25 20:08 +0000
        Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-26 01:31 +0100
        Re: Date arithmetic RobG <rgqld@iinet.net.au> - 2014-12-08 19:42 -0800
      Re: Date arithmetic "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-11-26 01:40 +0100
      Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-26 22:07 +0100
        Re: Date arithmetic RobG <rgqld@iinet.net.au> - 2014-12-08 21:41 -0800
          Re: Date arithmetic "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-12-09 09:47 +0100
          Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-12-09 14:17 +0100
          Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-12-10 23:34 +0000
            Re: Date arithmetic RobG <rgqld@iinet.net.au> - 2014-12-10 17:21 -0800
              Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-12-13 17:19 +0000
          Re: Date arithmetic RobG <rgqld@iinet.net.au> - 2014-12-10 18:35 -0800
  Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-11 22:29 +0100
    Re: Date arithmetic Swifty <steve.j.swift@gmail.com> - 2014-11-11 21:53 +0000
      Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-11 23:43 +0100
        Re: Date arithmetic John Harris <niam@jghnorth.org.uk.invalid> - 2014-11-12 15:49 +0000
  Re: Date arithmetic Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-11-12 19:58 +0000
  Re: Date arithmetic Dr.Kral@nyc.rr.com - 2014-11-13 20:24 -0500
    Re: Date arithmetic Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-11-14 04:34 +0100

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