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Date: Wed, 15 Mar 2017 20:41:00 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: DST change issue for timezones in southern hemisphere
On Wed, Mar 15, 2017 at 03:01:12PM -0400, Rich Felker wrote:
> On Mon, Mar 06, 2017 at 12:44:53PM +0200, JS wrote:
> > Hi!
> >
> > For some reason DST change in southern hemisphere occurs 1 hour late
> > when clock is turned backward and 1 hour early when clock is turned
> > forward.
> >
> > For example, timezone for spec for Brazil is:
> > BRT3BRST,M10.3.0/0,M2.3.0/0
> > Which means that DST change occurs at midnight.
> >
> > Output of date for both DST changes:
> >
> > ~# date
> > Sun Feb 19 00:59:59 BRST 2017
> > ~# date
> > Sun Feb 19 00:00:00 BRT 2017
> >
> > ~# date
> > Sat Oct 14 22:59:59 BRT 2017
> > ~# date
> > Sun Oct 15 00:00:00 BRST 2017
> >
> > I've tested the same code on same hardware but with uClibc library
> > instead of musl and it works fine.
>
> I think this is indeed a bug. Can you confirm that the correct
> progressions across DST change should be:
>
> Sat Feb 18 23:59:59 BRST 2017
> Sat Feb 18 23:00:00 BRT 2017
>
> Sat Oct 14 23:59:59 BRT 2017
> Sun Oct 15 01:00:00 BRST 2017
>
> If so I think I have a working fix (see attached). The logic for
> handling DST transition times for southern hemisphere was trying to do
> something special that was actually wrong and didn't need to be
> special-cased.
>
> Rich
> diff --git a/src/time/__tz.c b/src/time/__tz.c
> index 0e0c4ea..ffe8d40 100644
> --- a/src/time/__tz.c
> +++ b/src/time/__tz.c
> @@ -373,18 +373,14 @@ void __secs_to_zone(long long t, int local, int *isdst, long *offset, long *oppo
> long long t0 = rule_to_secs(r0, y);
> long long t1 = rule_to_secs(r1, y);
>
> + if (!local) {
> + t0 += __timezone;
> + t1 += dst_off;
> + }
> if (t0 < t1) {
> - if (!local) {
> - t0 += __timezone;
> - t1 += dst_off;
> - }
> if (t >= t0 && t < t1) goto dst;
> goto std;
> } else {
> - if (!local) {
> - t1 += __timezone;
> - t0 += dst_off;
> - }
> if (t >= t1 && t < t0) goto std;
> goto dst;
> }
Semantically this seems correct, so I'm applying it. Let me know if
you still find the behavior incorrect.
Thanks for reporting this.
Rich
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