Horton

Re: power() function in Windows: "value out of range: underflow"

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>, Huong Dangminh <huo-dangminh@ys.jp.nec.com>, Pg Hackers <pgsql-hackers@postgresql.org>, Akio Iwaasa <aki-iwaasa@vt.jp.nec.com>
Date: 2018-05-01T17:49:18Z
Lists: pgsql-bugs, pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Sun, Apr 29, 2018 at 7:24 PM, David Rowley
> <david.rowley@2ndquadrant.com> wrote:
>> I think we should back patch and try to be consistent about the
>> power(float8 1.0, 'NaN') and power('NaN', float8 0.0) cases. The
>> archives don't show any complaints about power() with NaN until this
>> one, so I imagine the number of people affected by this is small.

> I agree that this is not likely to affect a lot of people -- but the
> question isn't how many people will be affected but rather, of those
> that are, how many of them will be pleased rather than displeased by a
> change.  I would argue that the results have to be unambiguously wrong
> in the back-branches to justify a change there, and this doesn't
> appear to meet that standard. I would guess that the number of people
> who use NaN is very small, but those people have probably adapted
> their application to the behavior they are getting currently.

The point here, I think, is that you get behavior X on approximately 100%
of modern platforms, but (without this patch) behavior Y on some number of
older platforms.  People who have tested their app on a modern platform
and then find that it misbehaves on an old one will think this is a bug
fix.  People who only run their app on an old platform may think the
pre-patch behavior is fine, in which case they will indeed be upset if
we change it in a minor release.  Are there more of the latter than the
former?  I don't really know, and you don't either.  But I don't think
we should discount the existence of the former category.  Deploying
to production on an older release of $system than you develop on
is hardly an unusual scenario.

			regards, tom lane

Commits

  1. Revert back-branch changes in power()'s behavior for NaN inputs.

  2. Avoid wrong results for power() with NaN input on more platforms.

  3. Avoid wrong results for power() with NaN input on some platforms.