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Re: mktime loop
- From: Corinna Vinschen <corinna-cygwin at cygwin dot com>
- To: cygwin at cygwin dot com
- Date: Mon, 13 May 2013 17:49:21 +0200
- Subject: Re: mktime loop
- References: <5244063b734b165baf34bdebaff0aca5 at denis-excoffier dot org> <20130513153651 dot GD5045 at calimero dot vinschen dot de>
- Reply-to: cygwin at cygwin dot com
On May 13 17:36, Corinna Vinschen wrote:
> On May 13 09:08, Denis Excoffier wrote:
> > Hello,
> >
> > The following program (see below) is working properly under plain
> > 1.7.18. With all the snapshots afterwards (including
> > the current one 20130508), it fails after day=19, looping forever
> > (it seems). I use XP.
> >
> > Regards,
> >
> > Denis Excoffier.
> >
> > % cat foo.c
> > #include <stdio.h>
> > #include <time.h>
> >
> > int
> > main ()
> > {
> > int day;
> > // date --date='@2147483647' +%Y-%m-%d gives 2038-01-19
> > for ( day = 1 ; day <= 31 ; ++day ) {
> > struct tm tm;
> > time_t now;
> > tm.tm_year = 2038 - 1900;
> > tm.tm_mon = 1 - 1;
> > tm.tm_mday = day; // 19, 20
> > tm.tm_hour = 0;
> > tm.tm_min = 0;
> > tm.tm_sec = 0;
> > now = mktime (&tm);
> > fprintf (stderr, "day=%d\n", day);
> > };
> > return 0;
> > }
>
> Thanks for the testcase. This looks like the new BSD code I added
> lately assumes that the datatype time_t is 8 bytes, not 4 byte as on 32
> bit Cygwin. That's just a hunch I take from the fact that your testcase
> works fine on 64 bit Cygwin and only hangs on 32 bit Cygwin. Oh well.
> I'll investigate further...
Erm... hang on. Is that really a problem? 2147483647 is 0x7fffffff,
which is the maximum you get with a 4 byte time_t (== signed long)
anyway. If you switch the date to 2038-01-20, the value will be
negative, and therefore outside the scope of the 4 byte time_t. So this
is a hard restriction of using 4 byte time_t.
The solution is:
- Either somebody changes 32 bit Cygwin to 8 byte time_t while keeping
all the 4 byte time_t APIs intact to maintain compatibility with
existing binaries(*),
- or, you switch to a 64 bit Windows and use 64 bit Cygwin ;)
Corinna
(*) That's comparable with the off_t change from 4 to 8 byte we performed
when switching from Cygwin 1.3 to 1.5, and it will be a helluvalot
of work. Given the work we still have to do to get a 64 bit distro
up and running, this isn't exactly something I'm willing to invest a
lot of time into this year.
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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