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Date: Mon, 13 May 2013 17:49:21 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: mktime loop
Message-ID: <20130513154921.GF8890@calimero.vinschen.de>
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References: <5244063b734b165baf34bdebaff0aca5 AT denis-excoffier DOT org> <20130513153651 DOT GD5045 AT calimero DOT vinschen DOT de>
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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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