America/Chicago zone vs mktime w/tm_isdst!=-1

Dan Nelson dnelson at
Fri Dec 5 02:10:48 UTC 2003

In the last episode (Nov 28), Olson, Arthur David (NIH/NCI) said:
> The strange Chicago behavior occurs because for a few months back in
> 1936 Chicago switched to using Eastern Standard Time; mktime ended up
> using this information when trying to do a DST correction.
> The change below should "fix" things; it convinces mktime to work
> temporally backward through time adjustments that have been used in
> an area when trying to do a DST correction.
> (Of course if you really did start out with a 1936 time this is the
> wrong thing to do, but that's fairly unlikely.)

Looks like it works okay here.  Thanks!

	Dan Nelson
	dnelson at

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