Seeds the random number generator with seed or with a random value if no seed is given.
|Since 4.2.0||The seed becomes optional and defaults to a random value if omitted.|
|Since 5.2.1||The Mersenne Twister implementation in PHP now uses a new seeding algorithm by Richard Wagner. Identical seeds no longer produce the same sequence of values they did in previous versions. This behavior is not expected to change again, but it is considered unsafe to rely upon it nonetheless.|
// seed with microseconds
list($usec, $sec) = explode(' ', microtime());
return (float) $sec + ((float) $usec * 100000);
$randval = mt_rand();