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

Tom Lane tgl at sss.pgh.pa.us
Mon Nov 5 04:43:04 UTC 2018

Guy Harris <guy at alum.mit.edu> writes:
> I don't know what the lowest layers of Windows (NT) use (I don't have
> any "NT Native API" documentation handy), but the Windows API offers
> GetSystemTimeAsFileTime(), which supplies
> tenths-of-microseconds-since-the-FILETIME-epoch ("January 1, 1601
> (UTC)", using the proleptic Gregorian calendar and some
> probably-proleptic form of UTC), so it can do UTC as well.
> ...
> Caché runs atop Windows, assorted UN*Xes, and OpenVMS.  SYS$GETTIME on
> VMS supplies "the number of 100-nanosecond intervals since November 17,
> 1858."

In the department of weird epoch reference dates: I have a very distinct
recollection that HYDRA/C.mmp[1] ran their system clock in microseconds
since Charles Babbage's birthday (26 December 1791).  Unfortunately I
can't find any evidence other than 40-plus-year-old memory to support
that.  The C.mmp book cited by Wikipedia describes the clock as being
56 bits wide, which would be plenty for that timespan, but there's
nothing in it about the timekeeping convention.

			regards, tom lane

[1] https://en.wikipedia.org/wiki/C.mmp

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