41 lines
2.0 KiB
Diff
41 lines
2.0 KiB
Diff
From 48e68fbfd181f4c23a52021dc27cc45fea75fa25 Mon Sep 17 00:00:00 2001
|
|
From: Paul Eggert <eggert@cs.ucla.edu>
|
|
Date: Thu, 12 Nov 2020 12:45:42 -0800
|
|
Subject: [PATCH] Document "right" seconds better
|
|
|
|
* tz-link.html (Precision timekeeping):
|
|
Clarify "right" vs "posix" time_t.
|
|
---
|
|
tz-link.html | 15 +++++++++++++--
|
|
1 file changed, 13 insertions(+), 2 deletions(-)
|
|
|
|
diff --git a/tz-link.html b/tz-link.html
|
|
index 10c40b5..eb4a235 100644
|
|
--- a/tz-link.html
|
|
+++ b/tz-link.html
|
|
@@ -1034,8 +1034,19 @@ title="International Earth Rotation and Reference Systems Service">IERS</abbr>
|
|
Bulletins</a> contains official publications of the International
|
|
Earth Rotation and Reference Systems Service, which decides when leap
|
|
seconds occur. The <code><abbr>tz</abbr></code> code and data support leap seconds
|
|
-via an optional "<code>right</code>" configuration, as opposed to the
|
|
-default "<code>posix</code>" configuration.</li>
|
|
+via an optional "<code>right</code>" configuration where a computer's internal
|
|
+<code>time_t</code> integer clock counts every <abbr>TAI</abbr> second,
|
|
+as opposed to the default "<code>posix</code>" configuration
|
|
+where the internal clock ignores leap seconds.
|
|
+The two configurations agree for timestamps starting with 1972-01-01 00:00:00
|
|
+UTC (<code>time_t</code> 63 072 000) and diverge for
|
|
+timestamps starting with <code>time_t</code> 78 796 800,
|
|
+which corresponds to the first leap second
|
|
+1972-06-30 23:59:60 UTC in the "<code>right</code>" configuration, and to
|
|
+1972-07-01 00:00:00 UTC in the "<code>posix</code>" configuration.
|
|
+In practice the two configurations also agree for timestamps before
|
|
+1972 even though the historical situation is messy, partly because
|
|
+neither UTC nor TAI is well-defined for sufficiently-old timestamps.</li>
|
|
<li><a href="https://developers.google.com/time/smear">Leap Smear</a>
|
|
discusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
|
|
leap second so that they disagree with <abbr>UTC</abbr> by at most a
|
|
--
|
|
1.8.3.1
|
|
|