Date resources (YEARFRAC)

Just to be clear: There _ARE_ some resources that attempt to describe date calculations.
One of the best is "EMU AND MARKET CONVENTIONS: RECENT DEVELOPMENTS":
  http://www.isda.org/c_and_a/pdf/mktc1198.pdf 
I'm not certain that code can be unambiguously written from it (it's all prose and
no equations), but it's clearer than most.  For example, it shows multiple Actual/Actual
conventions. But (1) with only prose it's hard to be sure, and (2) there's no mapping
of these conventions to spreadsheet "Basis" values.  It's not even sure they map at all.
I'm trying to convert the text into code, but because it's prose that is NOT intended to
implemented by computer, it's hard to do easily.

Other sources are, of course, open source implementations' code.  Here is KOffice's:
http://api.kde.org/koffice-api/koffice-apidocs/kspread/html/helper_8cpp-source.html#l00194

I'm sure our friends from OpenOffice.org and others can point to similar files for their code,
in those cases where it's publicly accessible.

--- David A. Wheeler