This Perl module is a direct translation of Steffen Beyer's excellent
Date::Calc module to use Perl only instead of a combination of Perl and C.

This package consists of a Perl module for all kinds of date calculations
based on the Gregorian calendar (the one used in all western countries
today), thereby complying with all relevant norms and standards:
ISO/R 2015-1971, DIN 1355 and, to some extent, ISO 8601 (where applicable).

WWW: http://catcode.com/date/pcalc.html