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From: devine@vianet.UUCP (Bob Devine)
Newsgroups: net.lang.c
Subject: Re: Calendar Functions (simpler lea
Message-ID: <37@vianet.UUCP>
Date: Wed, 24-Sep-86 18:36:04 EDT
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Posted: Wed Sep 24 18:36:04 1986
Date-Received: Thu, 25-Sep-86 05:03:48 EDT
References: <34@vianet.UUCP> <86900058@haddock>
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haddock!karl (Karl W. Z. Heuer) writes:
[ that my suggestion of only checking if the year is divisible by
four assumes "the test is for the current year" and that "For a general
purpose algorithm (as per the original request), Dave's code is correct."]

  Not quite right.  I said just testing by use of "year % 4" is perfectly
fine for most uses (this is sort of like generic products.)  However, if
you want to test for years outside the range of 1901-2099 it doesn't work.
The UNIX value returned by the time() system call only covers the years
1970 +/- 67 years which falls nicely in the range.  The time() call is
unlikely to change.  If your system doesn't do it this way or you need a
larger range, don't use the simple test!

  A general purpose algorithm must also take care of years before the Gregorian
calendar system was adopted by a country.  Any KGB agents out there that
are reading this be sure to handle the years before 1918 differently :-)
So, the posted general purpose algorithm is not comprehensive in its
handling of years.  My initial posting simply indicated that if you are
not going to comprehensive, at least be a little faster.

> I believe the quadrimillennium correction was never officially adopted.
> It's not accounted for in cal(1).

  I'll check into the official rules; 'cal' is not a definite source. 
The Gregorian calender is about 1/2 minute too long compared to the solar
calendar which was quite close considering it was done by a 16th century
astronomer.  That means that there needs to be a day added in, oh, about
3,000 years.  Be sure to mark the date :-)


Bob Devine