Yo Warner! On Tue, 15 Jan 2019 17:45:32 -0700 Warner Losh <i...@bsdimp.com> wrote:
> > > Except that's not a leap second. struct tm doesn't do leap seconds > > > really. It kinda sorta does, but it kinda sorts doesn't. > > > > Well, it does in a modern Linux kernel. Otherwise NTPD would fail > > on the leap second, and that only happens every year so. :-) > > > > You are wrong. The kernel doesn't use struct tm. I never said the kernel uses struct tm. I said you can query the kernel for the time in a struct tm. > The kernel does this > by ticking either in TAI or by incrementing a TAI offset. ntpd uses a > different interface that exposes these things to it so it can > broadcast the leap second indicators correctly. Yup. > > > First, when you convert back and forth to time_t, you lose leap > > > second information. It's impossible to convert back and forth > > > from at least the UTC time zone. There's some 'right' time zones, > > > but they aren't strictly speaking POSIX compliant because it uses > > > the wrong math. Non-conforming, but damned useful and not wrong. > > > > Which is why you can't use time_t in UTC, but time_t in TAI > > can work, as well as struct tm, usually. Lot's of latent bugs... > > > > No. time_t is not TAI or GPS. It is UTC. Adjusted UTC. No, time_t is just a way to count seconds. See man difftime() for a use of time_t that is unrelated to any particular epoch. > It is the > number of SI seconds since 1970, minus all the positive leap seconds, > plus all the negative ones. Ciration please? I already cited the Linux doc that says otherwise. > > If you squint at it, GPS time (gps weeks, time of week) is just > > another notation very similar to time. And we know that works. > > > > GPS time has no leap seconds. It's a monotonic count since 1980. Correct. > > Since future leap seconds are unknown, and unknowable, there is no > > possible valid way to do this on the time scale of years. > > > > Correct. This is the fundamental flaw of UTC. Or a flaw of the universe. For some reason the earth refuses to rotate uniformly. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin
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