Last active
November 11, 2015 07:35
-
-
Save natmchugh/064ca5b6baae4cac734e to your computer and use it in GitHub Desktop.
A MersenneTwister implementation that gives the same values as PHP's internal value
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
<?php | |
class MersenneTwister | |
{ | |
// Create a length 624 array to store the state of the generator | |
private $MT; | |
private $index; | |
public function __construct($seed) | |
{ | |
$this->initialize_generator($seed); | |
} | |
public function setInternalState($state, $index) | |
{ | |
$this->MT = $state; | |
$this->index = $index; | |
} | |
// Initialize the generator from a seed | |
function initialize_generator($seed) { | |
$this->MT = new \SplFixedArray(624); | |
$this->index = 0; | |
$this->MT[0] = $seed; | |
for ($i = 1; $i < 624; $i++) { // loop over each other element | |
$this->MT[$i] = (0x6c078965 * ($this->MT[$i-1] ^ ($this->MT[$i-1] >> 30)) + $i) & 0xffffffff;// 0x6c078965 | |
} | |
} | |
// Extract a tempered pseudorandom number based on the index-th value, | |
// calling generate_numbers() every 624 numbers | |
function extract_number() { | |
if ($this->index == 0) { | |
$this->generate_numbers(); | |
} | |
$y = $this->MT[$this->index]; | |
$y = $y ^ ($y >> 11); | |
$y = $y ^ (($y << 7) & 0x9d2c5680); // 0x9d2c5680 | |
$y = $y ^ (($y << 15) & 0xefc60000); // 0xefc60000 | |
$y = $y ^ ($y >> 18); | |
$this->index = ($this->index + 1) % 624; | |
return $y >> 1; | |
} | |
// Generate an array of 624 untempered numbers | |
function generate_numbers() { | |
foreach ($this->MT as $i => $mt) { | |
$z = $mt; | |
$y = ($mt & 0x80000000) + ($this->MT[($i+1) % 624] & 0x7fffffff); // bits 0-30 (first 31 bits) of MT[...] | |
$this->MT[$i] = $this->MT[(($i + 397) % 624)] ^ ($y >> 1); | |
if (($z % 2) != 0) { // z is odd | |
$this->MT[$i] ^= 0x9908b0df; | |
} | |
} | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment