[PATCH] Incorrect decode from 64bit tzfile

[Milan Crha]

	Hello,
I've been looking onto a downstream bug
https://gitlab.gnome.org/GNOME/evolution/-/issues/1381
which exhibits as showing incorrect UTC offset for Asia/Kolkata time
zone.

Diving into the code the problem is that the times returned from

  $ zdump Asia/Kolkata -i

are like this:

   TZ="Asia/Kolkata"
   -	        -		+055328	LMT
   1854-06-27	23:59:52	+055320	HMT
   1869-12-31	23:27:50	+052110	MMT
   1906-01-01	00:08:50	+0530	IST
   1941-10-01	01		+0630		1
   1942-05-14	23		+0530	IST
   1942-09-01	01		+0630		1
   1945-10-14	23		+0530	IST

thus back in 1854 / 1869. The later, when truncated, is 2006, which
causes the wrong UTC offset, due to the code picking this change as the
nearest, even though the corresponding RRULE has set UNTIL (but this
information is not propagated in the 'changes' array).

I realized there's only a type cast error for little endian when
decoding 64bit values from the tzfile, which is easy to fix (and hard
to find). See the attached patch.

Checking what libical does now, it misses the 1854 transition, it
starts from 1869. It makes sense, because the num_trans are processed
from 1, not from 0. Starting from 0 does not help much, also because
there's missing the starting offset, thus I did not include it in this
patch.

This change does not fix an issue with reading tzfile in the slim
format, even I do not see much difference in the fat and slim formats
regarding the values read from it by the libical. It's still to be
investigated what fails there.

Good news is that before the patch the 'timezones' test returns:
 *** Summary: 425 zones tested, 2920 days failed, 152205 okay => 1% failed ***
while after the patch it returns:
 *** Summary: 425 zones tested, 1825 days failed, 153300 okay => 1% failed ***
thus there is an improvement.

Of course, the right thing would be to have 0 failed days there.
	Bye,
	Milan

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