Joda-Time might be helpful here. Gary
On Apr 14, 2012, at 1:02, Steve Hathaway <shath...@e-z.net> wrote: > Samuel, > > There are several ASF projects that could use a robust > implementation of Gregorian Calendar DateTime that > accommodates both (AD) Normal and (BC) Negative Years. > Such an algorithm is essential for mapping calendars of > antiquity to a robust solar time standard algorithm such > as exists in the Gregorian Calendar algorithm. > > If we can come up with an algorithm that implements > the Gregorian Calendar date-time functions in C, C++, and > Java -- I believe that the resulting code would > be gladly accepted in many of the other ASF projects. > > Even the organizations that support the web standards > consortium, will probably be interested in a solid > Gregorian date-time library (http://www.w3.org). > > The support of negative Gregorian Calendar Years is > beyond the initial scope of the EXSLT project. If we can > get a proof of concept and documentation for (BC) > date-time computations, I can assist in getting the > results published. > > If the EXSLT project only implements (AD) Gregorian > dates of positive years, that would be a big improvement > over what we have! > > > POS-CYCLE (AD) NEG-CYCLE (BC) > > 0001 not-leap -0400 not-leap Cycle Start Day = 0 > 0002 not-leap -0399 not-leap > 0003 not-leap -0398 not-leap > 0004 leap -0397 leap > 0008 leap -0393 leap > 0012 leap -0389 leap > 0016 leap -0385 leap > 0020 leap -0381 leap > 0100 not-leap -0301 not leap > 0200 not-leap -0201 not leap > 0300 not-leap -0101 not leap > 0400 leap -0001 leap Cycle End Day = 146096 > > Note: Within the NEG-CYCLE Gregorian, the months > and days have a monotonic positive sequence whereas > the years have a monotonic negative sequence. > > We cannot just perform a negative inverse of everything. > We just create a transposed Gregorian 400 year cycle > and iterate the days and months in a positive manner and > declare only the years as a negative inverse. > > Note also that leap-year analysis is done according to > the transposed Gregorian Cycle instead of the numeric > year value. > > An analysis of negative years (omitting Year = zero), it is > possible to create a useful algorithm for computing leap > years and leap centuries where Year is in the (BC) range. > > Converting Negative or (BC) Years to a useful numeric > for Positive Gregorian Cycle algorithms, just add the > appropriate 401, 801, 1201, 1601, 2001 to the negative > year, and the year result is transformed into a positive > number that is compatible with the simple leap-year > computation > > For example: Year -0397, add 0401, result = 4 which is a leap year. > Another example: Year -0201, add 0401, result = 200 which is not a leap > century. > > Calendars of antiquity are being positioned on the extrapolated > Gregorian calendar algorithm according to the above rules. > Maintaining the positive daily and monthly numbering also > allows positioning of various religious, secular, and public > festivals in their appropriate season when mapped to the other > calendars. > > The Unix "cal" calendar program does not allow negative > years for (BC) computation. > > ======================================================== > > - - - > -0800 = cycle start (day = 0) > -0797 a leap year > -0701 not a leap year > -0601 not a leap year > -0501 not a leap year > -0401 = cycle end (day = 146096) a leap year > - - - > -0400 = cycle start (day = 0) not a leap year > -0397 a leap year > -0301 not a leap year > -0201 not a leap year > -0101 not a leap year > -0001 = cycle end (day = 146096) a leap year > ========<epoc break>======= > 0001 = cycle start (day = 0) not a leap year > 0004 a leap year > 0100 not a leap year > 0200 not a leap year > 0300 not a leap year > 0400 = cycle end (day = 146096) a leap year > - - - > 0401 = cycle start (day = 0) > 0404 a leap year > 0500 not a leap year > 0600 not a leap year > 0700 not a leap year > 0800 = cycle end (day = 146096) a leap year > - - - > > ======================================== > Trivia: What year did King Harod die? > Answer: Year 4 (BC) Gregorian Calendar. > > Now, how did Rome determine that year 1 of the > Gregorian Calendar was to be the year of the birth > of Jesus, the Christ? (I have no answer.) > > Sincerely, > Steven J. Hathaway > Xalan Documentation Project > <shatha...@apache.org> > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: xalan-dev-unsubscr...@xml.apache.org > For additional commands, e-mail: xalan-dev-h...@xml.apache.org > --------------------------------------------------------------------- To unsubscribe, e-mail: xalan-dev-unsubscr...@xml.apache.org For additional commands, e-mail: xalan-dev-h...@xml.apache.org
