(PHP 4, PHP 5, PHP 7, PHP 8)
mt_srand — Seeds the Mersenne Twister Random Number Generator
$seed = 0, 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.
Because the Mt19937 (“Mersenne Twister”) engine accepts only a single 32 bit integer as the seed, the number of possible random sequences is limited to just 232 (i.e. 4,294,967,296), despite Mt19937’s huge period of 219937-1.
When relying on either implicit or explicit random seeding, duplications will appear much earlier. Duplicated seeds are expected with 50% probability after less than 80,000 randomly generated seeds according to the birthday problem. A 10% probability of a duplicated seed happens after randomly generating roughly 30,000 seeds.
This makes Mt19937 unsuitable for applications where duplicated sequences must not happen with more than a negligible probability. If reproducible seeding is required, both the Random\Engine\Xoshiro256StarStar and Random\Engine\PcgOneseq128XslRr64 engines support much larger seeds that are unlikely to collide randomly. If reproducibility is not required, the Random\Engine\Secure engine provides cryptographically secure randomness.
seedAn arbitrary int seed value.
modeUse one of the following constants to specify the implementation of the algorithm to use.
MT_RAND_MT19937:
The correct Mt19937 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.
|