Edit report at https://bugs.php.net/bug.php?id=63174&edit=1
ID: 63174
Updated by: bishop@php.net
Reported by: ub dot x7b8 at gmail dot com
Summary: Magic negative number generated by rand
Status: Assigned
Type: Bug
Package: *Math Functions
PHP Version: Irrelevant
Assigned To: bishop
Block user comment: N
Private report: N
New Comment:
Duplicated by #70003.
Previous Comments:
------------------------------------------------------------------------
[2015-07-09 15:52:03] bishop@php.net
@yohgaki That's because 3v4l runs 64-bit: http://3v4l.org/a8KaY
This problem only manifests when there's overflow on 32-bit platforms.
------------------------------------------------------------------------
[2015-07-08 21:50:55] yohgaki@php.net
It seems working well on 3v4l.
http://3v4l.org/BqqSr
------------------------------------------------------------------------
[2015-07-07 10:55:14] cmb@php.net
Related To: Bug #70003
------------------------------------------------------------------------
[2012-09-27 16:38:48] ub dot x7b8 at gmail dot com
Description:
------------
rand ( $min, getrandmax());
if $min < 0 then function generates number = getrandmax () - abs ( $min ) + 1 with very high
probability.
REPRODUCED: PHP 5.2.6-1 Debian 5.0.10 i386 under VmWare
REPRODUCED: PHP 5.2.6-1 Debian 5.0.5 i386
REPRODUCED: PHP 5.2.3, 5.2.8, 5.2.9, 5.4.7 Debian 6.0.4 i386 under VirtualBox
NOT REPRODUCED: PHP 5.2.1 Solaris 5.10 sparc
NOT REPRODUCED: PHP 5.2.9 Solaris 5.10 sparc
NOT REPRODUCED: PHP 4.4.4-8 Debian 4.0 i386 under VmWare
Test script:
---------------
<?php
$rand_min = -getrandmax (); # 2137483647
$rand_max = getrandmax ();
$c = 1000;
for ( $min = $rand_min; $min < 0; $min+=10000000 ) {
$diff = $rand_max - abs ( $min ) + 1;
$cnt = 0;
for ( $i = 0; $i < $c; $i++ ) {
$super_random_value = rand ( $min, $rand_max );
if ( $super_random_value == $diff ) $cnt++;
}
$per = $cnt * 100 / $c;
echo "Number '$diff' was generated $cnt times, " . $per . "%, minimum =
$min\n";
}
?>
Expected result:
----------------
Number '1' was generated 0 times, 0%, minimum = -2147483647
Number '10000001' was generated 0 times, 0%, minimum = -2137483647
Number '20000001' was generated 0 times, 0%, minimum = -2127483647
Number '30000001' was generated 0 times, 0%, minimum = -2117483647
Number '40000001' was generated 0 times, 0%, minimum = -2107483647
...skipped....
Number '2100000001' was generated 0 times, 0%, minimum = -47483647
Number '2110000001' was generated 0 times, 0%, minimum = -37483647
Number '2120000001' was generated 0 times, 0%, minimum = -27483647
Number '2130000001' was generated 0 times, 0%, minimum = -17483647
Number '2140000001' was generated 0 times, 0%, minimum = -7483647
Actual result:
--------------
Number '1' was generated 514 times, 51.4%, minimum = -2147483647
Number '10000001' was generated 507 times, 50.7%, minimum = -2137483647
Number '20000001' was generated 522 times, 52.2%, minimum = -2127483647
Number '30000001' was generated 520 times, 52%, minimum = -2117483647
Number '40000001' was generated 502 times, 50.2%, minimum = -2107483647
...skipped...
Number '2100000001' was generated 12 times, 1.2%, minimum = -47483647
Number '2110000001' was generated 14 times, 1.4%, minimum = -37483647
Number '2120000001' was generated 10 times, 1%, minimum = -27483647
Number '2130000001' was generated 11 times, 1.1%, minimum = -17483647
Number '2140000001' was generated 2 times, 0.2%, minimum = -7483647
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=63174&edit=1