Bug #63174 [Asn->Ver]: Magic negative number generated by rand

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 +Status: Verified Type: Bug Package: *Math Functions Operating System: 32bit PHP Version: Irrelevant Assigned To: bishop Block user comment: N Private report: N Previous Comments: ------------------------------------------------------------------------ [2015-07-09 16:12:04] bishop@php.net Duplicated by #70003. ------------------------------------------------------------------------ [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