Math Functions
PHP Manual

mt_srand

Seeds the Mersenne Twister Random Number Generator

Description

void mt_srand ([ int $seed [, int $mode = MT_RAND_MT19937 ]] )

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.

Parameters

seed

An arbitrary integer seed value.

mode

Use 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.

Return Values

No value is returned.

Changelog

Version Description
7.1.0 srand has been made an alias of mt_srand.
7.1.0 mt_randhas 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 paramter.
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.

Examples

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();
?>

See Also

  • mt_rand
  • mt_getrandmax
  • srand