Edit report at http://bugs.php.net/bug.php?id=46587&edit=1
ID: 46587
Comment by: belov1985 at gmail dot com
Reported by: atomo64 at gmail dot com
Summary: mt_/rand produce out of range numbers when min = 0
and max > get_randmax
Status: Closed
Type: Bug
Package: Math related
Operating System: Debian sid
PHP Version: 5.2.6
Assigned To: iliaa
Block user comment: N
Private report: N
New Comment:
Arr.. I use this feature five years!! ]:->
mt_rand(0, 10) - works, but mt_rand(10, 0) - why no? it's great, that
there is no need to check min & max...
WBR, Konstantin
Previous Comments:
------------------------------------------------------------------------
[2010-11-25 17:44:24] [email protected]
Automatic comment from SVN on behalf of cataphract
Revision: http://svn.php.net/viewvc/?view=revision&revision=305754
Log: - Fixed bug #53403 (use of unitialized values). Fixes the fix for
bug #46587.
- Added test for bug #46587.
------------------------------------------------------------------------
[2010-11-23 14:09:23] [email protected]
This bug has been fixed in SVN.
Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
Thank you for the report, and for helping us make PHP better.
------------------------------------------------------------------------
[2010-11-23 14:09:17] [email protected]
Automatic comment from SVN on behalf of iliaa
Revision: http://svn.php.net/viewvc/?view=revision&revision=305692
Log: Fixed bug #46587 (mt_rand() does not check that max is greater than
min).
------------------------------------------------------------------------
[2009-03-09 14:06:58] mmcnickle at gmail dot com
The problem is that there is an integer overflow on UL:
------------
<?php
define('UL',mt_getrandmax() + 1000);
var_dump(UL, (int)UL);
------------
will produce
------------
float(2147484647)
int(-2147482649)
------------
The $min and $max parameter names on mt_rand() (and rand()) are
misleading, as $min can be larger than $max and mt_rand will produce a
correct value between $min and $max.
In the bug example, the expected result is returned: a random value
between -2147482649 and 0.
If you want to change the integer overflow behaviour, it would be best
to do a check using mt_getrandmax() in the PHP code:
<?php
$max = mt_getrandmax() + 1000;
if ($max > mt_getrandmax()) {
$max = mt_getrandmax();
}
$r = mt_rand(0, $max); // $r is now a number between 0 and
mt_getrandmax()
------------------------------------------------------------------------
[2008-11-17 02:50:20] atomo64 at gmail dot com
Description:
------------
Whenever min is set to 0 and max is set to anything greater than
getrandmax (or the mt_ version) the returned PRN is always (despite
the upper limit check in the example code) a number minor than 0.
Reproduce code:
---------------
define("UL", mt_getrandmax()+1000);
$r=mt_rand(0, UL);
if ($r < 0 || $r > UL)
echo "Random value out of range\n";
Expected result:
----------------
No output
Actual result:
--------------
Random value out of range
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/bug.php?id=46587&edit=1
