#!/usr/bin/perl -w

use strict;

sub day_of_week {

    my ($year, $month, $day) = @_;

    my @offset  = (0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4);
    $year      -= $month < 3;

    return ($year + int($year/4) - int($year/100) + int($year/400)
                  + $offset[$month-1] + $day) % 7;
}


my $i=0;
for(my $time=1; $time<2**31; $time+=86400) {
    my ($mday,$mon,$year,$wday)=(localtime($time))[3..6];
    $mon++;
    $year+=1900;

    my $day=day_of_week($year,$mon,$mday);

    # progress info...
    print ((scalar localtime($time))," $day, $wday\n") unless ($i++%1000);

    if($day != $wday) {
        print "Mismatch between sub ($day) and localtime ($wday) for ",
               (scalar localtime($time)),"\n";
    }
}