Re: timezone dst transition

[Dan Eisenhut <deisenhut at wi dot rr dot com>]

On Wed, 2004-06-09 at 09:11, Andreas Schwab wrote:
> "Eisenhut, Daniel (MED)" <Daniel.Eisenhut@med.ge.com> writes:
> 
> > I'm working on an application that needs to know the date and time of
> > the next transition to or from daylight savings time.
> 
> See zdump(1).

I took a look at glibc/timezone/zdump.c.  It figures out the next
transition by taking the current time (as a time_t) in a local variable
and also a value 12 hours in the future.  It takes the broken down
versions of both and compares to see if tm_isdst has changed.  It
repeats at 12 hour increments until tm_isdst does change and then hunts
down where in that 12 hours it changes by using a halfing scheme.

This seems like a rather expensive operation compared to parsing the
TZif file (out of a ramdisk).  If this is the way zdump figures it out,
I take it that a way of directly accessing the transition time doesn't
exist in glibc.  Is there a glibc wishlist I could add to?

Thanks,
Dan