Question about localsub...

Andy Sautins sautins at
Mon Sep 18 20:29:23 UTC 1995

	I was pointed in the direction of this list about the question
I have.  If anyone can offer any help I'd really appreciate an email
response at sautins at

	I am writing an application that is continually needing to get
the offset from GMT for different times and different timezones.  The
method of setting the timezone environment variable, calling tzset,
and calling localtime is entirely too costly (mostly the time spent
opening and closing the timezone files).  In any case, I've been
perusing the code from ftp::/ and
am confused by the following piece of code from localsub:

	if (sp->timecnt == 0 || t < sp->ats[0]) {
		i = 0;
		while (sp->ttis[i].tt_isdst)
			if (++i >= sp->typecnt) {
				i = 0;
	} else {
>		for (i = 1; i < sp->timecnt; ++i)
>			if (t < sp->ats[i])
>				break;
>		i = sp->types[i - 1];
>	}
	ttisp = &sp->ttis[i];

	It seems that the only place that the time being converted is
used to determine which ttinfo struct is in the comparison with the
'ats' field.  The ats field is an array of time_t values, but for the
life of me I can't figure out how this would work.  

	My question is, how does this address the issue of, in May
it's is or is not daylight savings time?  I can't figure out how the
ats filed works.  From the header, it says that they are transition
times, but when looking at the debugger at the ast values and the all
seem to be large negative values.  Can anyone shed some light on
what's going on or point me in the direction of some documentation on
this algorithm?  

	Please direct responses to 'sautins at'

	Thank you VERY much.

	sautins at

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