77 lines
2.4 KiB
Diff
77 lines
2.4 KiB
Diff
From c983a0fb70b566b47502fe19dba62d7c298386e7 Mon Sep 17 00:00:00 2001
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From: Paul Eggert <eggert@cs.ucla.edu>
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Date: Mon, 7 Dec 2020 11:11:14 -0800
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Subject: [PATCH] Document zic coalescing zone+DST transitions
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* NEWS, zic.8: Document that zic coalesces transitions when
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a zone falls back just before DST springs forward.
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Document jump-back ambiguity
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* zic.8: Document avoidance of two nearly-simultanous transitions
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for Grand Turk.
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---
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NEWS | 5 +++++
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zic.8 | 30 ++++++++++++++++++++++++++++++
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2 files changed, 35 insertions(+)
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diff --git a/NEWS b/NEWS
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index dd131a9..bd9a2d2 100644
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--- a/NEWS
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+++ b/NEWS
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@@ -35,6 +35,11 @@ Unreleased, experimental changes
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returning to Eastern Time with US DST in 2018, rather than as
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maintaining EDT until 2015-11-01. (Thanks to P Chan.)
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+ Changes to documentation
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+
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+ The zic man page now documents zic's coalescing of transitions
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+ when a zone falls back just before DST springs forward.
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+
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Release 2020d - 2020-10-21 11:24:13 -0700
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diff --git a/zic.8 b/zic.8
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index dcd2fa3..2273dad 100644
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--- a/zic.8
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+++ b/zic.8
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@@ -590,6 +590,36 @@ first transition into standard time.
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In a single zone it is an error if two rules take effect at the same
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instant, or if two zone changes take effect at the same instant.
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.PP
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+If a continuation line subtracts from the UT offset after a transition that
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+would be interpreted to be later if using the continuation line's rules, the
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+.q "until"
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+time of the earlier zone or continuation line is interpreted according
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+to the continuation line's rules.
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+For example:
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+.br
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+.ne 7
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+.nf
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+.in +2m
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+.ta \w'# Rule\0\0'u +\w'NAME\0\0'u +\w'FROM\0\0'u +\w'max\0\0'u +\w'\*-\0\0'u +\w'Mar\0\0'u +\w'Sun>=8\0\0'u +\w'2:00\0\0'u +\w'SAVE\0\0'u
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+.sp
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+# Rule NAME FROM TO \*- IN ON AT SAVE LETTER/S
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+Rule US 2007 max \*- Mar Sun>=8 2:00 1:00 D
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+Rule US 2007 max \*- Nov Sun>=1 2:00 0 S
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+.ta \w'Zone\0\0America/Grand_Turk\0\0'u +\w'STDOFF\0\0'u +\w'RULES\0\0'u +\w'FORMAT\0\0'u
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+# Zone\0\0NAME STDOFF RULES FORMAT [UNTIL]
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+Zone\0\0America/Grand_Turk \*-4:00 \*- AST 2018 Mar 11 2:00
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+ \*-5:00 US E%sT
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+.sp
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+.in
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+.fi
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+Here, an incorrect reading would be there were two clock changes on 2018-03-11,
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+the first from 02:00 AST (\*-04) to 01:00 EST (\*-05),
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+and the second an hour later from 02:00 EST (\*-05) to 03:00 EDT (\*-04).
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+However,
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+.B zic
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+interprets this more sensibly as a single transition from 02:00 AST (\*-04) to
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+02:00 EDT (\*-04).
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+.PP
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A link line has the form
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.sp
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.nf
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--
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1.8.3.1
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