The Date::Calc module will let you do date computations back to the year 1 C.E.. The Delta_Days function should be just what you need.

  my $dd=Delta_Days(1,1,1,$cur_yr,$cur_mo,$cur_da);
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If you're interested in how to do the calculation by hand I highly recommend checking out Calenderical Calculations by Derschowitz and Reingold. Should be available at any bookstore w/ a reasonably complete techincal section.

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Looking at vrooms answer and mine reminds me that you need to be careful in how you define epoch. In general terms eopch is the start-date of your calendar. So when does your calendar start ???

1. Jan 1, 1970 (unix Epoch)
2. Jan 1, 1900 (another epoch used in computers)
3. Jan 1, 1 (Gregorian epoch)
4. etc..

In my answer I had assumed the Gregorian epoch. If you want your "time from epoch" in seconds and your epoch is 1/1/1970 then the time() function returns that.