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Message-ID: <20240325185339.GG4163@brightrain.aerifal.cx>
Date: Mon, 25 Mar 2024 14:53:39 -0400
From: Rich Felker <dalias@...c.org>
To: Alexander Weps <exander77@...me>
Cc: musl@...ts.openwall.com
Subject: Re: Broken mktime calculations when crossing DST boundary
On Mon, Mar 25, 2024 at 06:28:14PM +0000, Alexander Weps wrote:
> On Monday, March 25th, 2024 at 19:02, Rich Felker <dalias@...c.org> wrote:
>
> > On Mon, Mar 25, 2024 at 09:42:53AM -0400, Rich Felker wrote:
> >
> > > On Mon, Mar 25, 2024 at 01:24:57PM +0000, Alexander Weps wrote:
> > >
> > > > See below.
> > > >
> > > > AW
> > > >
> > > > On Monday, March 25th, 2024 at 14:13, Rich Felker dalias@...c.org wrote:
> > > >
> > > > > On Mon, Mar 25, 2024 at 12:55:28PM +0000, Alexander Weps wrote:
> > > > >
> > > > > > > If you take your test program and switch it to initialize with
> > > > > > > tm_mday=31, then do -=1 instead of +=1, you'll find that it gives
> > > > > > > 2011-12-29 01:00:00 -10 as well, only now it seems like the correct,
> > > > > > > expected thing to happen. Any change to "fix" the case you're
> > > > > > > complaining about would necessarily break this case.
> > > > > >
> > > > > > So (- day, +day):
> > > > > >
> > > > > > Musl:
> > > > > > 2011-12-31 01:00:00 +14
> > > > > > 2011-12-29 01:00:00 -10
> > > > > > 2011-12-29 01:00:00 -10
> > > > > >
> > > > > > Glibc:
> > > > > > 2012-01-01 01:00:00 +14
> > > > > > 2011-12-31 01:00:00 +14
> > > > > > 2012-01-01 01:00:00 +14
> > > > > >
> > > > > > Seems like musl doesn't even interpret the initial struct tm
> > > > > > correctly in that case. It is off by day.
> > > > > >
> > > > > > Because December only had 30 days, 31s day after normalization is
> > > > > > January 1st.
> > > > >
> > > > > This is nonsense. December has a day 31, which you can clearly see
> > > > > from the glibc output. For this particular year in this zone, with the
> > > > > zone rule change, there are "only 30 days" in December, but they are
> > > > > numbered 1-29 and 31, not 1-30.
> > > >
> > > > You confuse day of month which is represented in tm_mday with
> > > > calendar day that is interpreted by strftime.
> > > >
> > > > You said to set tm_mday = 31, which would be January 1st after normalization.
> > > > December 31s is 30th day of month represented as tm_mday = 30.
> > >
> > > OK, I meant tm_mday=31-1.
> >
> >
> > Um, no, where did you get that idea? I just assumed you were right
> > because I always forget which tm_* are off-by-1, but tm_mday is
> > one-based not zero-based:
> >
> > int tm_mday; // day of the month -- [1, 31]
> >
> > (per the standard). So how did you end up getting the wrong thing? Are
> > you even running the code you say you are?
> >
>
> I have to sincerely ask if you are feeling ok?
> You seem not able to follow this conversation.
>
> What idea do you mean?
> Also you have the codes. You can like "I don't know" run them yourself?
> You question I run those codes without trying to run them yourself? Again?!
> What is going on?
The first few pieces of code you posted did not work because they
depended on other code you did not include, so I stopped trying to run
them.
> Maybe I reiterate some basic facts for you and that will put you
> back on track.
>
> This was an example from an article provided earlier in this thread (by somebody).
> We are in TZ=Pacific/Apia.
> The 30th December was skipped in 2011. There was no December 30th.
> So, there were only 30 days in December.
> 30th day of the month December was December 31st.
>
> And run those examples yourself. I have no idea why I am being
> questioned if they generate the output when you can easily verify it
> yourself.
Which piece of self-contained, actually-runnable code would you like
me to look at that demonstrates something wrong? (i.e. not something I
have already said is behaving as expected)
Rich
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