Horton

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

Huong Dangminh <huo-dangminh@ys.jp.nec.com>

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From: Huong Dangminh <huo-dangminh@ys.jp.nec.com>
To: "pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>, Akio Iwaasa <aki-iwaasa@vt.jp.nec.com>
Date: 2018-04-10T08:30:19Z
Lists: pgsql-bugs, pgsql-hackers

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Hi,

There are some cases that power() function does not work 
correctly with 'NaN' arguments in Windows environment.
Something like,

postgres=# select power('NaN',11);
ERROR:  value out of range: underflow
postgres=# select power('NaN','NaN');
ERROR:  value out of range: underflow
postgres=# select power(11,'NaN');
ERROR:  value out of range: underflow

In Linux environment, instead of ERROR it returns 'NaN'.

The reason here is,
When pow() in float.c:dpow() is called with 'NaN' arguments,
pow() returns 'NaN' but in Windows environment errno is set to 
EDOM(invalid floating-point exception).
So, PostgreSQL update "result" and cause an ERROR in CHECKFLOATVAL macro.

I think it should be return 'NaN' in all of above cases.
I have tried to create a patch to fix it.
Please confirm the attached file.


---
Thanks and best regards,
Dang Minh Huong
NEC Solution Innovators, Ltd.
http://www.nec-solutioninnovators.co.jp/en/

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.