On 02/23/2018 10:08 AM, Paul Gilmartin wrote: > On Fri, 23 Feb 2018 07:24:36 -0800, Charles Mills wrote: > >> There are two more or less redundant fields in the CVT: CVTTZ and CVTLDTO. >> (CVTLDTO is actually in CVT extension 2.) CVTLDTO contains the exact local >> time offset in timer units -- in other words, you can add it directly to an >> STCK value. CVTTZ is identical to the high order word (only) of CVTLDTO -- >> in other words, it is the *approximate* offset in units of 1.048576 seconds. >> (Approximate because you cannot represent an integral number of hours >> exactly in units of 1.048576 seconds.) Why 1.048576? One way of looking at >> that value is that it is 2^20 divided by 10^6. It is the ratio between mibi >> and mega. >> > An IBM Redbook has called this a megamicrosecond. Ugh! Humpty Dumpty! And now that we have international standards for binary prefixes, if it were named today it would be mebimicroseconds, or maybe Miµsec (the short prefix form is "Mi" for "M-ega b-i-nary", the longer pronounceable forms use the first two letters of each prefix word, so is "mebi" not "mibi"). Still ugly, but unambiguously 2^20✕10^(-6) seconds. JC Ewing > >> Are there possible timing windows? Yes, all over the place. (Between a STCK >> and inspecting CVTLDTO? Yes, a small window. What about someone else's STCK >> that is somehow passed to you and your inspecting CVTLDTO? Potentially a >> window of seconds, days or even years.) I have come to the conclusion that >> local time is something that it is impossible to deal with perfectly. You >> deal with it as well as you can. >> > It can be done a lot better than x/OS does it, and with no timing hazard: > https://en.wikipedia.org/wiki/Tz_database > > Dismayingly, provincially, z/OS shuns the Olson database. NIH!? > > -- gil >
-- Joel C. Ewing, Bentonville, AR jcew...@acm.org ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
