Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!husc6!panda!genrad!decvax!ima!haddock!karl
From: karl@haddock
Newsgroups: net.lang.c
Subject: Re: Calendar Functions (simpler lea
Message-ID: <86900058@haddock>
Date: Thu, 18-Sep-86 09:54:00 EDT
Article-I.D.: haddock.86900058
Posted: Thu Sep 18 09:54:00 1986
Date-Received: Sat, 20-Sep-86 00:15:15 EDT
References: <34@vianet.UUCP>
Lines: 23
Nf-ID: #R:vianet.UUCP:34:haddock:86900058:000:996
Nf-From: haddock!karl    Sep 18 09:54:00 1986


vianet!devine (Bob Devine) writes:
>Dave Lewis writes:
>>   if (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0))
>
>While this works, it is overkill.  Unless you believe that your
>code will make it to the year 2100, a simple test for divisibility
>by 4 is sufficient.

It looks like you're assuming the test is for the current year.  For a
general-purpose algorithm (as per the original request), Dave's code is
correct.  If the input is a 32-bit signed integer measuring seconds since
1970 (a common implementation of time_t), then the range is contained in
(1900,2100) and the simpler algorithm works -- but this is probably not a
good assumption to make; an unsigned long will reach past 2100.

>If you really want an algorithm for all years,
>you then need to also test for years divisible by 4000...

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

Karl W. Z. Heuer (ima!haddock!karl; karl@haddock.isc.com), The Walking Lint