Re: Interval aggregate regression failure (expected seems

I assume no more progress has been made on this?

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Tom Lane wrote:
> I wrote:
> > Michael Paesold <mpaesold(at)gmx(dot)at> writes:
> >> I am definatly not going to use -march=pentium4 in any production
> >> system. Should I open a bug report with RedHat (gcc vendor)?
>
> > Yeah, but they'll probably want a smaller test case than "Postgres fails
> > its regression tests" :-(
>
> I have just confirmed that the problem still exists in FC4's current
> compiler (gcc 4.0.1, gcc-4.0.1-4.fc4), which probably will boost up the
> priority of the complaint quite a long way in Red Hat's eyes.
>
> I've also confirmed that the problem is in interval_div; you can
> reproduce the failure with
>
> select '41 years 1 mon 11 days'::interval / 10;
>
> which should give '4 years 1 mon 9 days 26:24:00', but when
> timestamp.o is compiled with "-mcpu=pentium4 -march=pentium4",
> you get '4 years 1 mon 10 days 02:24:00'. --enable-integer-datetimes
> is not relevant because the interesting part is all double/integer
> arithmetic.
>
> Looking at this, though, I wonder if the pentium4 answer isn't "more
> correct". If I'm doing the math by hand correctly, what we end up
> with is having to cascade 3/10ths of a month down into the days field,
> and since the conversion factor is supposed to be 30 days/month, that
> should be exactly 9 days. Plus the one full day from the 11/10 days
> gives 10 days. I think what is happening on all the non-Pentium
> platforms is that (3.0/10.0)*30.0 is producing something just a shade
> less than 9.0, whereas the Pentium gives 9.0 or a shade over, possibly
> due to rearrangement of the calculation. I think we can still file this
> as a compiler bug, because I'm pretty sure the C spec does not allow
> rearrangement of floating-point calculations ... but we might want to
> think about tweaking the code's roundoff behavior just a bit.
>
> An example that's a little easier to look at is
>
> select '41 years 1 mon'::interval / 10;
>
> I get '4 years 1 mon 9 days' with the pentium4 optimization, and
> '4 years 1 mon 8 days 24:00:00' without, and the former seems more
> correct...
>
> regards, tom lane
>
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