Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rutgers!mcnc!uvaarpa!vger!g_harrison
From: g_harrison@vger.nsu.edu
Newsgroups: comp.lang.pascal
Subject: Re: Algorithm needed
Message-ID: <46.27140d61@vger.nsu.edu>
Date: 11 Oct 90 10:12:48 GMT
References: <3334@vela.acs.oakland.edu> <1990Oct10.175221.17285@uwasa.fi>
Lines: 58

In article <1990Oct10.175221.17285@uwasa.fi>, ts@uwasa.fi (Timo Salmi) writes:
> In article <3334@vela.acs.oakland.edu> moconnor@argo.acs.oakland.edu writes:
>>Could someone please mail me code such that given a date (something
>>like, say, October 10th, 1990), it tells me the day of the week?
........
>  A1: There is a wkdayfn function in /pc/ts/tspas22.arc Turbo Pascal
> units collection to give the modern weekday based on Zeller's
> congruence. Also you can find a more extensive Julian and Gregorian
> weekday algorithm in Dr.Dobbs Journal, June 1989, p. 148. Furthermore
> Press & Flannery & al, Numerical Recipes, has the weekday code.
> 
>  A2: Some will recommend the following kludge.  Store the current
>  .....etc......
> 
> The wares (/pc/ts/tspas22.arc) are available by anonymous ftp from
> chyde.uwasa.fi, Vaasa, Finland, 128.214.12.3, or by using our mail
>  .....etc......
> Prof. Timo Salmi        (Moderating at anon. ftp site 128.214.12.3)
> School of Business Studies, University of Vaasa, SF-65101, Finland
> Internet: ts@chyde.uwasa.fi Funet: gado::salmi Bitnet: salmi@finfun

I sent the following Pascal function to the original poster.  It's very nice
and VERY fast.  I found it in "Computer Language Magazine" a few years ago:

....................................................................
	MONTHTYPE = 1..12;	{January..December}
	DAYTYPE   = 1..7;	{Sunday..Saturday}

{returns the first day of the MONTH in YEAR}
function FIRST_DAY(MONTH : MONTHTYPE; YEAR  : INTEGER) : DAYTYPE; 
var
    	DAY, MON, YEA : INTEGER; 
begin
	YEA := YEAR;
    	MON := MONTH;

    	if MON <= 2 then 
	begin
      		MON := MON + 12; 
      		YEA := YEA - 1
	end;

    	DAY := (3 + (2*MON) + (((MON + 1)*6) div 10) + YEA + (YEA div 4) - 
		(YEA div 100) + (YEA div 400)) mod 7; 

    	if DAY = 0 then 
      		FIRST_DAY := 7
    	else 
      		FIRST_DAY := DAY
end;

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-- George C. Harrison                 INTERNET: g_harrison@vger.nsu.EDU --
-- Professor of Computer Science               Subliminal Address:  adA --
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