Dates
Fast calendar calculations for 10,000 years (Julian and Gregorian)
... the chiliads. So how will you be able to do date calculations if you then even try to consider time gimmicks like summer/winter time changes, leap-seconds and so on? Just forget it!
This project gives you very short pure date routines that are the fastest ones that you can get, because they don't need any looping for doing their calculations, and they do their calculations from 1/1/0 up to 12/31/9999. Of course they precisely consider the transition from Julian to Gregorian calendar. ;-)