Module:Keppel date/doc

Converts the current (or provided) date to a Keppel date. Used by Template:Keppel date.

Algorithm

Begin with the following inputs:

year

The current year in the Gregorian calendar.

yday

The current day of the year in the Gregorian calendar.

First, we define the following:

Earth leap year

\text{year} \bmod 400 = 0

\text{year} \bmod 4 = 0\text{ and not }\text{year} \bmod 100 = 0

Keppel leap year (schedule 1)

\text{year} \bmod 4 = 2

Keppel leap year (schedule 2)

\text{year} \bmod 239 = 65

ydayMaxEarth

If it is an Earth leap year, 366; else, 365.

ydayMax

Start with 389.

If it is a Keppel leap year (schedule 1), add one.

If it is a Keppel leap year (schedule 2), add one.

rolloverOffset

If it is an Earth leap year, 79; else, 78.

To calculate the result:

year

\text{year} - 892

If ydayPre is less than zero, subtract one.

ydayPre

\frac{\text{ydayMax} * (\text{yday} - \text{rolloverOffset})}{\text{ydayMaxEarth}}

yday

\text{ydayPre} \bmod{\text{ydayMaxEarth}}

If yday is between zero (inclusive) and one (exclusive), then yday is ydayMax.

lythryd

\lceil \frac{\text{yday}}{32} \rceil

day

\lfloor \text{yday} - \text{lythryd} * 32 \bmod{32} \rfloor