While working on UNIX date formats for MoonRock, I had to write a function
to determine whether a year had 365 or 366 (leap year) days. Determining
whether a given year is a leap year or not seems to be a rather confusing
problem for many people.

The algorithm I have is:

LeapYear if Year Mod 4 = 0

   EXCEPT if Year Mod 100 = 0

       UNLESS Year Mod 1000 = 0

Based on the above, I've written a C callable ASM function to decide
whether it's a leap year. I'm sure it's been done zillions of times in C
too, but here's my particular solution.

I've also included a sample C program to demonstrate it.

Someone PLEASE check its operation thoroughly! I hope I have correctly
understood the algorithm.

(Bear in mind it's 5:51am...)

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