I finally implemented those JForth words in REBOL and am in the process of
submitting a script to rebol.org. Look for it there in a day or so. I'll
probably have to make some cosmetic changes to get it through their ROBOT.
Russell [EMAIL PROTECTED]
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, November 02, 1999 2:07 PM
Subject: [REBOL] epoch? Re:(8)
> [snip - some algorithms]
>
> [EMAIL PROTECTED] wrote:
> >That appears to be a Julian day referenced to the start of the year. My
> >understanding of a Julian day number is that it is the number of days
since
> >the start of the current Julian period, which started noon Jan 1 4713 BC.
>
> That's what a Julian date is in the real world :)
> As a computer term, a Julian date is any date calculated in the same
> manner as a real world Julian date, but possibly from a different base
> date. Whatever the base date is, that's called the epoch. The epoch
> for Unix is 1-Jan-1970, for DOS it's 1-Jan-1980. There are problems
> similar to Y2K when Julian date counters overflow or roll over.
>
> >Noon of Dec 31 1998 was the beginning of JD 2,451,179. There is an
> >algorithm for calculating this number from a given date in the Gregorian
> >Calendar, our present calendar, but I don't have it at hand. It requires
> >the use of a floor or ceiling function, the nearest integer smaller (or
> >greater) than a given decimal number. The formula accounts for leap
years
> >and the days in each month. It also starts a year on March 1, so
February
> >is the last month, and the formula truncates its length correctly. I
> >implemented the formula in Forth using integers, but it was long ago -- .
>
> I don't know about anyone else here, but I'd be interested in seeing
> that algorithm if you could dig it up, even in Forth :)
>
> Brian
>
