From: Operating system: Linux PHP version: Irrelevant Package: *General Issues Bug Type: Bug Bug description:rand(0,limit) fail to hit the 0 often
Description: ------------ I notices that something in my code not giving expected result and when digging some more I notices that rand(0,limit) don't give the same "opportunity" to that '0'. in other words, the random distribution is very bad. in a 10,000 calls to random like this: rand(0,7), I noticed that the 0 hit only 2000 while 1,2,3,4,5,6,7 all hit about 16300 times. this is a ratio of 770% If the range start with number bigger than 0, it works well. ex. rand(1,8)-1 work correctly but rand(0,7) doesn't --- >From manual page: http://www.php.net/function.rand#refsect1-function.rand- description --- Test script: --------------- $ar =array('AA','BB','CC','DD','EE','FF','GG'); $cnt=array(); $len=count($ar)-1; for($i=0;$i<100000;$i++){ $c = $ar[rand(0,$len)]; @$cnt[$c]++; } print_r($cnt); ---- result: [BB] => 16245 [AA] => 2003 [FF] => 16260 [EE] => 16281 [DD] => 16369 [GG] => 16508 [CC] => 16334 Expected result: ---------------- the expected result of course should be that rand(0,limit) over many calls will distribute the hits evenly between all the range -- Edit bug report at https://bugs.php.net/bug.php?id=60420&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=60420&r=trysnapshot54 Try a snapshot (PHP 5.3): https://bugs.php.net/fix.php?id=60420&r=trysnapshot53 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=60420&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=60420&r=fixed Fixed in SVN and need be documented: https://bugs.php.net/fix.php?id=60420&r=needdocs Fixed in release: https://bugs.php.net/fix.php?id=60420&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=60420&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=60420&r=needscript Try newer version: https://bugs.php.net/fix.php?id=60420&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=60420&r=support Expected behavior: https://bugs.php.net/fix.php?id=60420&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=60420&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=60420&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=60420&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=60420&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=60420&r=dst IIS Stability: https://bugs.php.net/fix.php?id=60420&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=60420&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=60420&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=60420&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=60420&r=mysqlcfg
