(PHP 4, PHP 5, PHP 7)
mt_srand — Seeds the Mersenne Twister Random Number Generator
$seed
[, int $mode = MT_RAND_MT19937
]] ) : void
Seeds the random number generator with
seed or with a random value
if no seed is given.
Note: There is no need to seed the random number generator with srand() or mt_srand() as this is done automatically.
seedAn arbitrary integer seed value.
modeUse one of the following constants to specify the implementation of the algorithm to use.
| Constant | Description |
|---|---|
MT_RAND_MT19937 |
Uses the fixed, correct, Mersenne Twister implementation, available as of PHP 7.1.0. |
MT_RAND_PHP |
Uses an incorrect Mersenne Twister implementation which was used as the default up till PHP 7.1.0. This mode is available for backward compatibility. |
No value is returned.
| Version | Description |
|---|---|
| 7.1.0 | srand() has been made an alias of mt_srand(). |
| 7.1.0 |
mt_rand() has been updated to use the fixed, correct, version of
the Mersenne Twister algorithm. To fall back to the old behaviour, use mt_srand() with MT_RAND_PHP as the second parameter.
|
| 5.2.1 | The Mersenne Twister implementation in PHP now uses a new seeding algorithm by Richard Wagner. Identical seeds no longer produce the same sequence of values they did in previous versions. This behavior is not expected to change again, but it is considered unsafe to rely upon it nonetheless. |
Example #1 mt_srand() example
<?php
// seed with microseconds
function make_seed()
{
list($usec, $sec) = explode(' ', microtime());
return $sec + $usec * 1000000;
}
mt_srand(make_seed());
$randval = mt_rand();
?>