lmaher@uokvax.UUCP (01/23/84)
#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
foertsch@uiucuxc.UUCP (01/28/84)
#R:sequent:-33700:uiucuxc:3300047:000:267 uiucuxc!foertsch Jan 27 13:17:00 1984 Warning: In the preceding congruence, January and February are considered to be the last two months of the previous year!!!! This means that c and d as well as m must be adjusted from their conventional numberings in order to apply the formula given. Kurt Hirchert
bill@utastro.UUCP (William H. Jefferys) (02/06/84)
The question was whether common date algorithms will die in the
year 2000. Actually, probably not since, unlike the century
years 1700, 1800 and 1900, the year 2000 *is* a leap year. 2100
is *not* a leap year, so if one has naively programmed the date
algorithm to count a leap year every 4 years, it is likely that
it will work until then.
--
Bill Jefferys 8-%
Astronomy Dept, University of Texas, Austin TX 78712 (USnail)
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