Hi Mark,
The U2 conversion code source code is not public so we can only guess. The
method used by OpenQM was recently changed to correct problems with dates
way back in history and is essentially as follows. It sounds complex but it
is mostly just a series of division operations.....
1. Add 718430 to the day number. This gives a datum of 1 January 0001 to
simplify things. (QM documents that it doesn't support BC dates and that we
don't allow for the calendar changes in 1752 or 1583 depending on where you
live).
2. Divide by 146097 to work out how many 400 year cycles we have completed.
This allows for the complications of leap year calculations.
3. Work out how many 100 year cycles we are into the remaining years from
step 2.
4. Work out how many 4 year cycles we are into the remaining years from step
3.
5. Calcualte whole years into the current 4 year cycle.
6. Decide if this is a leap year.
7. Work out the calendar date within the year.
8. Now that we know the day/month/year, apply the conversion code to
construct the actual date string.
Our date conversions also have codes for 1st, 2nd, 3rd,... style dates and
for ISO week numbers. The ISO week calculation is even more horrific but is
well documented on the web (http://personal.ecu.edu/mccartyr/ISOwdALG.txt).
Martin Phillips
Ladybridge Systems Ltd
17b Coldstream Lane, Hardingstone, Northampton, NN4 6DB
+44-(0)1604-709200
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