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From: cdr@brahms.amd.com (Carl Rigney)
Newsgroups: comp.lang.perl
Subject: Re: Perl subroutine libraries?
Summary: zeller's congruence
Keywords: weekday perl subroutine
Message-ID: <1990Oct2.172114.6421@amd.com>
Date: 2 Oct 90 17:21:14 GMT
References: <11802@bsu-cs.bsu.edu>
Sender: usenet@amd.com (NNTP Posting)
Organization: Advanced Micro Devices; Sunnyvale, CA
Lines: 34

Here's a simple subroutine to calculate Day of the Week using
Zeller's Congruence, which I've found very useful.  A lot of
the temporary variables could be omitted by making it harder to read.

If Randal wants to turn it into a one-liner that's fine by me. :-)

#!/usr/local/bin/perl
# usage: zeller yyyy mm dd

$day = &weekday(@ARGV);
print $day,"\n";

sub weekday {
	local($year,$month,$day)=@_;
	local($y,$m,$c,$yy,$z);

	local(@wday) = ( "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" );

	$y = $year;
	$m = ($month + 10) % 12;
	$y-- if ($m > 10);
	$c = int ( $y / 100 );
	$yy = $year % 100;

	$z = ( int ( (26*$m - 2)/10) + $day + $yy + int($yy/4) + int ($c/4) - 2*$c ) % 7;
	return $wday[$z];
}

--
Carl Rigney
cdr@amd.com
{ames decwrl sun uunet}!amdcad!cdr

"There are no problems in perl, only opportunities for adventure."