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Doc Bug #65852 Wrong documentation about NAN comparison
Submitted: 2013-10-07 17:46 UTC Modified: 2017-01-28 16:33 UTC
From: chalkerx at gmail dot com Assigned: cmb (profile)
Status: Closed Package: Documentation problem
PHP Version: 5.5.4 OS: Linux
Private report: No CVE-ID: None
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 [2013-10-07 17:46 UTC] chalkerx at gmail dot com 
Description:
------------
http://www.php.net/manual/en/types.comparisons.php states:
> Some numeric operations can result in a value represented by the constant NAN. Any loose or strict comparisons of this value against any other value, including itself, will have a result of FALSE

But that is invalid, because NAN loosely equals to boolean true.

Test script:
---------------
var_dump(sqrt(-1));
var_dump(sqrt(-1) == true);

Expected result:
----------------
As per documentation, the result should be:

double(NAN)
bool(false)

The documentation should be consistent with what actually happens.

Actual result:
--------------
double(NAN)
bool(true)

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 [2013-10-07 17:48 UTC] chalkerx at gmail dot com
-Summary: Fileinfo file() method and any mp3 file crashes php. +Summary: Wrong documentation about NAN comparison.
 [2013-10-07 17:48 UTC] chalkerx at gmail dot com 
Whoops, browser-saved title from the old bug.
 [2013-10-09 09:23 UTC] phpmpan at mpan dot pl 
As documentation states, conversion from NaN to boolean should yield TRUE, and hence TRUE == TRUE will be TRUE too.

I believe the wording is just not precise and "value" means "numeric value" in this case. Of course this needs to be fixed.
 [2017-01-28 16:29 UTC] cmb@php.net
-Summary: Wrong documentation about NAN comparison. +Summary: Wrong documentation about NAN comparison -Status: Open +Status: Verified -Assigned To: +Assigned To: cmb
 [2017-01-28 16:29 UTC] cmb@php.net 
> I believe the wording is just not precise and "value" means
> "numeric value" in this case.

Even comparing non-numeric strings with NAN yields FALSE[1]. The
sole exception appears to be TRUE[2].

[1] <https://3v4l.org/orCLn>
[2] <https://3v4l.org/VY7oe>
 [2017-01-28 16:32 UTC] cmb@php.net 
Automatic comment from SVN on behalf of cmb
Revision: http://svn.php.net/viewvc/?view=revision&amp;revision=341793
Log: Fix #65852: Wrong documentation about NAN comparison
 [2017-01-28 16:33 UTC] cmb@php.net
-Status: Verified +Status: Closed
 [2017-01-28 16:33 UTC] cmb@php.net 
This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.
 [2020-02-07 06:06 UTC] phpdocbot@php.net 
Automatic comment on behalf of cmb
Revision: http://git.php.net/?p=doc/en.git;a=commit;h=0ade9d91c1e45a8afef45c9ee514fccdc1900ca1
Log: Fix #65852: Wrong documentation about NAN comparison
 
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