[tz] Epic fail for DST fallback in hospital health records

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Mon Nov 5 05:27:27 UTC 2018

On 2018-11-04 19:11, Guy Harris wrote:
> On Nov 4, 2018, at 5:59 PM, Guy Harris wrote:
>> So it's probably just that Epic never got DST handling right.
> Back in 1979, UNIX wasn't as big a platform that sort of application as it
> is now; if they started on VMS (I don't know whether it had a "get the time
> in UTC" API back then) or on MVS (I'm not sure what it offers), maybe using
> local time was a more obvious choice, but you'd still think they'd know that
> stuff does happen at hospitals between 1 AM and 3 AM on Sunday, so...

[Open]VMS provides a 64 bit time with 100ns resolution from the MJD epoch of
1858-11-17, but the update frequency and accuracy depends on interval timer
frequency, which may be as low as 100Hz/10ms.

IBM S/390 (System z) STCK stores a 64 bit time with a resolution of 1/4096us
from the NTP epoch 1900-01-01, updated with a frequency equivalent to
incrementing bit 51 (big endian) every us.

Most TZ and DST issues result from app designers and/or implementors thinking
they understand what systems should do during changeovers, and trying to
implement it themselves, possibly undoing the correct behaviour of a tested
time/zone/DST handling library.

Regulators ensure that the electrical power industry has had a good handle on
dealing with local times and 23-25 hour days for decades.

OTOH my Motorola PVR broadcast schedule/cable program guide properly showed two
periods from 01.00-02.00; but a European sports series broadcast after the
switch skipped recording the first hour Sunday morning early-ish local time!

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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