#43171 [NEW]: nonrandom rand() results in lower bits
From: bdew at druzya dot org
Operating system: windows xp sp2
PHP version: 5.2.4
PHP Bug Type: Math related
Bug description: nonrandom rand() results in lower bits
Description:
------------
Under windows xp cli version, rand() seems to return cycling values in
lower bits.
If i use rand(x,y) the bug does happen only when max_rand+2>y>max_rand+2
mt_rand() is unaffected
Tested same code under linux cli and the bug doesn't happen.
possibly related to http://bugs.php.net/bug.php?id=43108
Reproduce code:
---------------
$a=rand() & 0xff;
for ($k=0;$k<10;$k++) {
$i=0;
do {
$i++;
$b=rand() & 0xff;
} while ($a!=$b);
echo("cycle: $i\n");
};
Expected result:
----------------
10 lines with "cycle: x", x being different every line
Actual result:
--------------
cycle: 256
cycle: 256
cycle: 256
cycle: 256
cycle: 256
cycle: 256
cycle: 256
cycle: 256
cycle: 256
cycle: 256
every time
--
Edit bug report at http://bugs.php.net/?id=43171&edit=1
--
Try a CVS snapshot (PHP 4.4): http://bugs.php.net/fix.php?id=43171&r=trysnapshot44
Try a CVS snapshot (PHP 5.2): http://bugs.php.net/fix.php?id=43171&r=trysnapshot52
Try a CVS snapshot (PHP 5.3): http://bugs.php.net/fix.php?id=43171&r=trysnapshot53
Try a CVS snapshot (PHP 6.0): http://bugs.php.net/fix.php?id=43171&r=trysnapshot60
Fixed in CVS: http://bugs.php.net/fix.php?id=43171&r=fixedcvs
Fixed in release: http://bugs.php.net/fix.php?id=43171&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=43171&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=43171&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=43171&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=43171&r=support
Expected behavior: http://bugs.php.net/fix.php?id=43171&r=notwrong
Not enough info: http://bugs.php.net/fix.php?id=43171&r=notenoughinfo
Submitted twice: http://bugs.php.net/fix.php?id=43171&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=43171&r=globals
PHP 3 support discontinued: http://bugs.php.net/fix.php?id=43171&r=php3
Daylight Savings: http://bugs.php.net/fix.php?id=43171&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=43171&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=43171&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=43171&r=float
No Zend Extensions: http://bugs.php.net/fix.php?id=43171&r=nozend
MySQL Configuration Error: http://bugs.php.net/fix.php?id=43171&r=mysqlcfg
Thread (3 messages)
- bdew at druzya dot org