sub days_since_1900 {
   use integer;
   my ($d, $m, $y) = @_;
   # $d: 1-based Day of the month (1..31)
   # $m: 0-based Month (Jan=0..Dec=11)
   # $y: 2 or 4 digit year
   $y += 1900 if $y < 1000;
   my $i = ($m + 10) % 12;
   my $j = $y - $i/10;
   return $d + 365*$j + $j/4 - $j/100 + $j/400 + ($i*306 + 5)/10 - 693
+902;
}

[download]

Based on Time::Local's internals.

Update: Fixed a misnamed variable. Thanks liverpole.
Update: Added missing - 693902. Thanks rodion. Where was my head when I posted this?!

In reply to Re: subroutine for calculating day since 1900 needed by ikegami
in thread subroutine for calculating day since 1900 needed by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.