At 4:36 PM +0000 on 01/09/2011, john gilmore wrote about Date
representations: Y2k revisited:
Internal date formats are much simpler and not at all controversial
among coloro che sanno. Choose an epoch origin, the putative birth
date of Jesus, that of the Moslem hegira, Scaliger's -4713 January 1
BCE, whatever; give it the serial number +1, its predecessor days
the serial number 0, -1, -2, . . . , and its successor days the
serial numbers +2, +3, +4, . . . Whatever your choice, conversion
to someone else's choice is trivial; a single addition|subtraction
suffices.
It is not as simple as that since you have to allow for calenders
getting out of sync. When the Julian calender was replaced by the
Gregorian one, there were (depending on where you were since the
switch occurred in different years in different countries) 13 or so
days lost. There is also the issue that the length of the years has
varied so that saying the day number x is date y in the calendar can
be difficult (all years were not 365/366 days long).
Then there is the issue of when leap years occur. Author Isaac Asimov
write a mystery story ("Year of the Action") about when the Gilbert
and Sullivan Operetta "Pirates of Penzance" was set. All that is
stated in the play is that one of the characters who was born on
February 29 would celebrate his 21st birthday in 1940. The play
occurs on the 21st anniversary of his birth (at which point he is
5.25 Birthdays Old). If he was born in 1856 (84 years before 1940)
then the play was set in 1877. The problem is that 1900 was NOT a
leap year which if the 1940 year is accurate would push the birth
date back to 1852 and thus the "Year of the Action" to 1873. The
mystery was to decide from the other dialog on the year 1873 (which
would not count 1900 as a leap year) or 1877 (which would assume that
Gilbert goofed and was unaware of the problem with 1900).
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [email protected] with the message: GET IBM-MAIN INFO
Search the archives at http://bama.ua.edu/archives/ibm-main.html
