Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!tut.cis.ohio-state.edu!ucsd!telesoft!mclow
From: mclow@telesoft.telesoft.com (Marshall Clow @telesoft)
Newsgroups: comp.sys.mac
Subject: Re: Week DAYS (was Re: why 1904?  ms excel)
Summary: Neat Trick
Message-ID: <488@telesoft.telesoft.com>
Date: 9 Sep 89 07:11:58 GMT
References: <457a7553.1285f@maize.engin.umich.edu> <972@mrsvr.UUCP>
Organization: TeleSoft, San Diego, CA.
Lines: 14

In article <972@mrsvr.UUCP>, hallett@shoreland.uucp (Jeff Hallett x4-6328) writes:
> Interesting.  One thing I've always wondered about, though, is, given
> a date in the Gregorian calendar, how does one determine the day of
> the week?  There is obviously a brute force approach, but does someone
> know (and will relate) an elegant solution?

A trick I used in writing some routines was to notice that in any 400
year period there are 97 leap years and 303 non-leap years for a total
of  146097 days, which is divisible by 7! This means that Jan 01, 1 is
the same day of the week as Jan 01, 2001. ( Tuesday, if I remember ).
From there, you can grunt the answer out.

	Marshall Clow
	mclow@telesoft.com