I think it's done now.
- fixed an issue where the years weren't being calculated properly (?!)
- I may be slightly out of sync with the official documentation, at least according to the tests I've done on my local so far. This year should match up, and so will key dates (New Year Day and Leap Day). I've shifted leap years to fall on multiples of 4 so calculating would be a simple case of if mod 4 is 0, it's a leap year, if mod 128 is 0, it's not a leap year, so some of my years will be a day or two out
theabysmal_calendar.info
name = theAbysmal Calendar
description = Converts Gregorian date to theAbysmal date
core = 7.x
package = Date/Time
theabysmal_calendar.module