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

Edit report at https://bugs.php.net/bug.php?id=63174&edit=1 ID: 63174 Updated by: cmb@php.net Reported by: ub dot x7b8 at gmail dot com Summary: Magic negative number generated by rand Status: Verified Type: Bug Package: *Math Functions Operating System: 32bit PHP Version: Irrelevant Assigned To: bishop Block user comment: N Private report: N New Comment: > This problem only manifests when there's overflow on 32-bit > platforms. ACK. However, on 64bit platforms there's a closely related problem if $max-$min > PHP_INT_MAX, in which case rand() unevenly distributes, e.g. running <?php for ($i = 0; $i < 1000000; $i++) { if (rand(PHP_INT_MIN, PHP_INT_MAX) > 0) { echo "Never\n"; break; } } ?> never prints "Never". The problem is in RAND_RANGE() where only the offset is calculated as double, instead of the whole expression (see the attached patch "rand-range-double"). This change would also fix the behavior on 32bit architectures. However, changing the results of (mt_)rand() for $max-$min > PHP_INT_MAX and with regard to inexact double to integer conversion on 64bit architectures would be a BC break, so I'm not sure whether we should apply that for PHP 5. IMHO, changing PHP 7 in this regard would be acceptable even though it's in feature freeze. Anyway, I would suggest to better document the behavior for non default ranges. Previous Comments: ------------------------------------------------------------------------ [2015-07-15 22:32:49] cmb@php.net The following patch has been added/updated: Patch Name: rand-range-double Revision: 1436999569 URL: https://bugs.php.net/patch-display.php?bug=63174&patch=rand-range-double&revision=1436999569 ------------------------------------------------------------------------ [2015-07-13 20:06:48] bishop@php.net https://github.com/php/php-src/pull/1416 ------------------------------------------------------------------------ [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 ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=63174 -- Edit this bug report at https://bugs.php.net/bug.php?id=63174&edit=1