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bug#22034: time-utc->date shows bogus zone-dependent leap second

From: John Cowan
Subject: bug#22034: time-utc->date shows bogus zone-dependent leap second
Date: Sun, 21 Oct 2018 22:38:55 -0400

On Sat, Oct 20, 2018 at 5:43 PM Mark H Weaver <address@hidden> wrote:

If I understand correctly, 'time-utc->date' should never return a date
object with 60 in the seconds field, because those extra seconds have no
representation in time-utc.  They only have representations in time-tai
and time-monotonic.

As I understand it, this is incorrect.  UTC days can contain either 86400 or 86401 seconds (or in principle a different number), depending on whether the day has a leap second.  It is *Posix* time, not UTC time, that contains a fixed number of seconds per day, or more accurately that assigns a label from 0 to 864399 to the seconds of a day, and can assign the same label to more than one second (or in principle could assign one or more labels to no second) on a leap-second day. Consequently, a broken-down time can indeed return 60 in the seconds field, but only for a UTC clock, never for a Posix clock.

This error is repeated in a number of your later messages, but I'll respond only to this one.

John Cowan          http://vrici.lojban.org/~cowan        address@hidden
Tautology is something that is tautological.  --Francois-Rene Rideau

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