Pete Forman <pete.forman@westerngeco.com> writes:
> It is fairly arbitrary what the answer to this question is: if six
> months is subtracted from a to give b, should a.local.hour =
> b.local.hour or should a.utc.hour = b.utc.hour? If you want the
> former then set tm_isdst = -1 before calling mktime.
It's not arbitrary: we want the former. Anything else generates
bug reports from people who expect "9/1/2000 - six months" to
produce "3/1/2000", not sometime late in the evening of 2/29/2000.
regards, tom lane