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

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.

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