Bug #67043 [Opn]: substr_compare falsely reports equality on negative offset

From: Date: Tue, 08 Apr 2014 09:53:26 +0000
Subject: Bug #67043 [Opn]: substr_compare falsely reports equality on negative offset
References: 1  Groups: php.bugs 
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Edit report at https://bugs.php.net/bug.php?id=67043&edit=1

 ID:                 67043
 User updated by:    php at kirk dot at
 Reported by:        php at kirk dot at
 Summary:            substr_compare falsely reports equality on negative
                     offset
 Status:             Open
 Type:               Bug
 Package:            Strings related
-Operating System:   OS X
+Operating System:   any
 PHP Version:        5.5.11
 Block user comment: N
 Private report:     N

 New Comment:

Saw this bug on multiple OSes, therefore changing OS to any.


Previous Comments:
------------------------------------------------------------------------
[2014-04-08 09:40:19] php at kirk dot at

Description:
------------
Since version 5.5.11 a substr_compare with a negative 3rd parameter (=offset, thus it should start
counting from the end of the string) incorrectly reports equality.

See http://3v4l.org/8co5P

I believe the bug could have been introduced in this commit: https://github.com/datibbaw/php-src/commit/e292391b3899ed2d80a8f44dc94074d68328c6ea

What caught my eye is the introduced cast to an unsigned integer but I don't know if this
really is the source of the bug.

Workaround: specify a length (absolute value of the negative offset)

Test script:
---------------
var_dump(substr_compare("template", "_emplate", -8));
var_dump(substr_compare("template", "_emplate", -8, 8));

Expected result:
----------------
int(21)
int(21)

Actual result:
--------------
int(0)
int(21)


------------------------------------------------------------------------



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Edit this bug report at https://bugs.php.net/bug.php?id=67043&edit=1

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