From:	SMTP%"DCantor@chqsplay.mv.com" 28-JAN-1995 11:08:22.26
To:	EVERHART
CC:	
Subj:	Re: VMS quadword time to UNIX time

From: DCantor@chqsplay.mv.com (David A. Cantor)
X-Newsgroups: comp.os.vms
Subject: Re: VMS quadword time to UNIX time
Message-ID: <791269989.42snx@chqsplay.mv.com>
Date: Sat, 28 Jan 95 05:13:09 GMT
Organization: My Own Disorganization
Lines: 18
To: Info-VAX@Mvb.Saic.Com
X-Gateway-Source-Info: USENET

In article <3gbc8f$820@crl.crl.com> fgodino@crl.com writes:
>
>Looking for a routine or algorithim to convert the VMS quadword time
> to UNIX time (a long word value)..
>
>Promblem is VMS has a zero base date of NOV 18. 1858 and Unix is Jan 1 1970

VMS maintains a count of 100nsec units which have elapsed since
18-Nov-1858 00:00:00.0000000 in the quadword.  (If you divide this number
by 864,000,000,000 (the number of 100nsec units in one day), you get the
so-called Modified Julian Date (MJD).)  Unix maintains a count of full
seconds elapsed since 1-Jan-1970 00:00:00 .  (Both ignore the leap seconds
which have occured, of course, so we can ignore them here, too.)

To convert from VMS time to Unix time, divide the 64-bit VMS integer value 
by 10,000,000 and subtract the product of 40587 (that's the MJD for 
1-Jan-1970) and 86400 (the number of seconds in one day) from the integer 
portion of the quotient.