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This code calculates the DoY (Day of Year, 1-366) WITHOUT accessing any hardcoded values or variables. Might be useful for calendar applications. It takes into account leap years, according to the Gregorian calendar rules (years divisible by 4 are leap, but years divisible by 100 are not leap, unless they are also divisible by 400), so it will produce correct results for any date in the Gregorian calendar (after 1582 AD, or whatever year the Gregorian calendar was adopted in your country). Expects the year (>1581) in eax, the month (1-12) in ecx and the day (1-31) in edx. Does not check for date validity. Preserves Windows registers. Currently I've tried to use as few instructions as possible, so speed or size optimizations are possible. Returns the DoY in eax.

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