Re: The 8-Byte Two-Step

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From	Christian Neukirchen <chneukirchen@gmail.com>
Newsgroups	comp.misc
Subject	Re: The 8-Byte Two-Step
Date	Tue, 23 Sep 2014 18:26:59 +0200
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Marko Rauhamaa <marko@pacujo.net> writes:

> Bob Eager <news0002@eager.cx>:
>
>> On Sun, 21 Sep 2014 00:48:44 +0300, Marko Rauhamaa wrote:
>>> def gregorian_day_count(isodate):
>>>     year, month, day = map(int, isodate.split('-'))
>>>     a, b = divmod(12 * year + month + 1185, 12)
>>>     return int(a * 365.2425) + int(30.573 * b + 0.706) + day
>>
>> [...]
>>
>> Didn't know that one...thanks!
>
> Except, you shouldn't believe everything you read on the Internet :) --
> the above code had a bug which I noticed when I actually tested it.
>
> Here's a correction:
>
>    def gregorian_day_count(isodate):
>        year, month, day = map(int, isodate.split('-'))
>        a, b = divmod(12 * year + month - 3, 12)
>        yeardays = a * 365 + a // 4 - a // 100 + a // 400
>        return yeardays + int(30.573 * b + 0.706) + day
>
> If you intend to use the code, you're well advised to test it yourself.

I found this one, which is similar in spirit but doesn't depend on
floats:

http://alcor.concordia.ca/~gpkatch/gdate-algorithm.html

function g(y,m,d)
  m = (m + 9) % 12
  y = y - m/10
  return 365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + ( d - 1 )

-- 
Christian Neukirchen  <chneukirchen@gmail.com>  http://chneukirchen.org

Thread

The 8-Byte Two-Step Rich <rich@example.invalid> - 2014-09-20 20:41 +0000
  Re: The 8-Byte Two-Step Bob Eager <news0002@eager.cx> - 2014-09-20 21:14 +0000
    Re: The 8-Byte Two-Step Marko Rauhamaa <marko@pacujo.net> - 2014-09-21 00:48 +0300
      Re: The 8-Byte Two-Step Bob Eager <news0002@eager.cx> - 2014-09-21 08:27 +0000
        Re: The 8-Byte Two-Step Marko Rauhamaa <marko@pacujo.net> - 2014-09-21 14:14 +0300
          Re: The 8-Byte Two-Step Marko Rauhamaa <marko@pacujo.net> - 2014-09-23 11:19 +0300
          Re: The 8-Byte Two-Step Christian Neukirchen <chneukirchen@gmail.com> - 2014-09-23 18:26 +0200
      Re: The 8-Byte Two-Step mm0fmf <none@mailinator.com> - 2014-09-21 20:45 +0100
  Re: The 8-Byte Two-Step Sylvia Else <sylvia@not.at.this.address> - 2014-09-21 13:42 +1000

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