This template computes the Gregorian serial day. This is the day number according to the proleptic Gregorian calendar, with 1-1-1 as number 1. It works for all years, and is exact for at least the years from -100,000,000,000 until 100,000,000,000. The input is in parameters 1, 2, 3 for the year, the month number and the day.
It is demonstrated on the page Help:Demo of function time.
It uses function
#time after reducing the year number to one in the range of this function, and converts the result to compensate for this reduction.