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From: edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.))
Newsgroups: comp.sys.handhelds
Subject: Re: Julian/Gregorian Conversions
Keywords: julian
Message-ID: <21281@shlump.nac.dec.com>
Date: 20 Mar 91 13:49:10 GMT
References: <27e668c5:2479comp.sys.handhelds@hpcvbbs.UUCP> <1991Mar20.005301.3647@ux1.cso.uiuc.edu>
Sender: newsdaemon@shlump.nac.dec.com
Reply-To: edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.))
Organization: Digital Equipment Corporation
Lines: 33

In article <1991Mar20.005301.3647@ux1.cso.uiuc.edu>,
lnk10562@uxa.cso.uiuc.edu (Louis Koziarz) writes:

>Could someone/anyone post the simple date->julian date algorithm in
>pseudo-code?

    Credit for the formulas used for the date conversions goes to the PPC
    ROM User's Manual, specifically Roger Hill and Fernando Lopez-Lopez.

Calendar (year, month, day) to Julian day number:
	y' = year + (month-2.85)/12
	julian = floor(
		floor(floor(367*y')-floor(y')-.75*floor(y')) +
		d - .75*floor(y'/100)
	) + 1721115
Julian day number to Calendar:
	j' = julian-172119.2
	n' = ceiling(j'+j'/48699+.2)
	y' = floor((n'-.2)/365.25)
	n'' = n'-floor(y'*365.25) = ceiling(.2 + (n'-.2)%365.25)
	m' = floor((n''-.5)/30.6)
	day = floor(n''-30.6*m'+.5) = ceiling((m'-.5)%30.6)
	if (m' <= 9)
		month = m'+3
		year = y'
	else
		month = m'-9
		year = y'+1


				-- edp (Eric Postpischil)
				"Always mount a scratch monkey."
				edp@jareth.enet.dec.com