[tz] iana build failures on Windows

[Paul Eggert]

On 4/22/21 11:22 PM, Manuela Friedrich wrote:

> please find the tracing output attached.

Thanks. Here's the first line that differs between your output (-) and 
mine (+):

-TRACING: lotm_ok=1 tm_ok=1 only_ok=0 lot=-1830384001 t=-1830383664 
tm={1911-364T23:49:28 dst=0} lotm={1911-364T23:43:51 dst=0} delta=337 
t-lot=337
+TRACING: lotm_ok=1 tm_ok=1 only_ok=0 lot=-1830383326 t=-1830382989 
tm={1912-000T00:16:51 dst=0} lotm={1911-364T23:55:06 dst=0} delta=1305 
t-lot=337

This difference suggests that for TZ=Africa/Abidjan and the timestamp 
-1830383495, tzdb's localtime behaves differently on your platform than 
on mine, although the two platforms agree on -1830384001 and on 
-1830382989 (the point of disagreement is halfway between the two points 
of agreement). localtime should convert this timestamp to 1911-12-31 
23:52:17 -00:16:08 LMT (with no DST), but evidently it converts to 
something else on your platform.

I see three things that could have gone wrong. First, while looking into 
this I noticed that relevant parts of zic.c and localtime.c rely on 
implementation-defined behavior when shifting or converting negative 
integers. Although I doubt that's your problem please try the latest 
GitHub tzdb development version, which has these fixes I installed today:

https://mm.icann.org/pipermail/tz/2021-April/030025.html
https://mm.icann.org/pipermail/tz/2021-April/030024.html

Second, the TZif file for Africa/Abidjan could be incorrect on your 
platform, which would mean a portability bug in zic.c. I'm attaching my 
Abidjan file (it's binary data) along with Abidjan-od-t-x1.txt, the 
output of the shell command 'od -t x1 Africa/Abidjan' (it's a textual 
representation of that data). Please compare this to your Abidjan file, 
making sure that it's the actual Abidjan file you're using (you perhaps 
have multiple near-copies of that file on your system by now...).

Third, there could be a problem in tzdb's localtime code. To test this, 
please apply the attached patch zdump-2.diff to otherwise-unmodified 
source code and then run 'zdump Africa/Abidjan' (without the '-v'). The 
output I get is also attached as zdump-2.txt; what output do you get?
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0000000 54 5a 69 66 32 00 00 00 00 00 00 00 00 00 00 00
0000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0000040 00 00 00 00 00 00 00 01 00 00 00 01 00 00 00 00
0000060 00 00 00 54 5a 69 66 32 00 00 00 00 00 00 00 00
0000100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0000120 00 00 00 00 00 00 01 00 00 00 02 00 00 00 08 ff
0000140 ff ff ff 92 e6 92 48 01 ff ff fc 38 00 00 00 00
0000160 00 00 00 04 4c 4d 54 00 47 4d 54 00 0a 47 4d 54
0000200 30 0a
0000202
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Africa/Abidjan  
t=-1830383495 sp->ats[0]=-1830383032 sp->timecnt=1
sp->ats[sp->timecnt-1]=-1830383032 sp->goback=0 sp->goahead=0
i=sp->defaulttype=0
ttisp->tt_utoff=-968
 localsub={1911-365 1911-12-31 23:52:17 dst=0}
Sun Dec 31 23:52:17 1911 LMT