Home » PHP » PHP_Compat » Bug #9043

[2006-10-15 10:49 UTC] jo at durchholz dot org

Description:
------------
There are two things wrong with str_shuffle:
1) It shouldn't seed mt_srand. For PHP < 4.2, people should be seeding the random number generators in the main program, and for PHP > 4.2, it's unnecessary (actually bad on a fast machine because it may reseed within the same microsecond).
2) Appending to the result string ($new) causes quadratic behavior. Either append to an array and implode() it on return, or create a string and swap characters inside it.

Here's code that swaps characters (drop-in replacement for the function's body).
Warning: Untested.

$result = (string) $str;
for ($i = strlen ($str) - 1; $i >= 0; $i--) {
// Swap random character from [0..$i] to position [$i].
$j = mt_rand (0, $i);
$tmp = $str [$i];
$str [$i] = $str [$j];
$str [$j] = $tmp;
}
return $result;

[2006-12-14 11:12 UTC] jo at durchholz dot org

Hope you fixed my mistake.
(The loop should be reading and updating $result instead of $str.)