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From: lmaher@uokvax.UUCP
Newsgroups: net.followup
Subject: Re: Date Algorithm - (nf)
Message-ID: <5070@uiucdcs.UUCP>
Date: Sun, 22-Jan-84 22:57:32 EST
Article-I.D.: uiucdcs.5070
Posted: Sun Jan 22 22:57:32 1984
Date-Received: Fri, 27-Jan-84 04:53:22 EST
Lines: 23

#R:sequent:-33700:uokvax:2700015:000:661
uokvax!lmaher    Jan 21 15:25:00 1984

(posting from a friend's account while uok is down)
For calculating the day of the week, here's Zeller's Congruence:

F = (int((26*m-2)/10) + k + d + int(d/4) + int(c/4) - 2*c) mod 7

F=0 is Sunday, F=1 is Monday, and so on
k is the day of the month, c is centuries, d is year in the century,
m is the month starting with March as 1, April as 2, on to February
as 12. int(x) is the largest integer smaller than x, of course.

Example:  8/20/1982 - k=20,c=19,d=82,m=6
F= (int(15.4) + 20 + 82 + int(20.5) + int(4.75) - 38) mod 7
  = (15+20+82+20+4-38) mod 7
  = 103 mod 7
  = 5
so August 20, 1982 was a Friday.

	Carl
	..!uokvax!uok!crigney 
	..!duke!uok!crigney