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.TOPIC.......: Fdate's Leap Year Algorithm
.DISCUSSION..:
Here is how Fdate decides whether or not a year is a leap year.

• Every year evenly divisible by 4 IS a leap year
  • EXCEPT THAT
    • Every year evenly divisible by 100 IS NOT a leap year
      • EXCEPT THAT
        • Every year evenly divisible by 400 IS a leap year.

Using this algorithm:

• 1983 is not a leap year
• 1984 is a leap year
• 1900 is not a leap year
• 2000 is a leap year
  
  

See "A Machine Algorithm for Processing Calendar Dates", by Henry F. Fliegel (Georgetown University Observatory) and Thomas C. Van Flandern (U.S. Naval Observatory) COMMUNICATIONS OF THE ACM, Volume 11, Number 10, October 1968