[PUSHED][PATCH] fdo#44456 added calc function DATEDIF as in ODF 1.2

[Winfried Donkers]

Hi Eike,

> This took a little longer than I expected as I had to figure out what Excel
> actually does in DATEDIF. Please see
> https://bugs.freedesktop.org/show_bug.cgi?id=44456
> for changes I did and test case document. For the final algorithm of the
> function itself best take a look at the current interpr2.cxx as I spoiled it in
> between myself ...

You did a lot of work! I expected some or a lot of comments on my interpretations
of ODF1.2 as i don't have Excel to compare with, but you did all the work yourself!
 I'm a volunteer, I don't mind cleaning up (my own) mess :)

> Some detailed nitpicks in commit comments :-)

If I'm correct, the main changes are that  my interpretation of ignore years/months were not right.
There is one thing I am not very happy about: DATEDIF in calc now does not accept date1 to be later (larger) than date2. IMHO this should be possible as it is a very normal possibilty. It looks as if DATEDIF does not accept this condition because Excel doesn't/can't. I thought calc conforms to ODF and can export to xls(x) but with possible loss of functionality. Now it is like LibreOffice is an open source copy of MS Office.
I would very much like to adjust the code to make it possible again for date1 to be later (larger) than date2, both to increase its use :) and because I don't want to be a follower of MS Office :(

> Thanks for getting this going!

And a big thank you for all your corrections/inprovements!
I hope to be able to send in more formula based patches, I like this area:)

Winfried