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MersenneTwister.php
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MersenneTwister.php
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<?php
namespace Eris\Random;
use RuntimeException;
class MersenneTwister implements Source
{
private $seed;
private $index;
private $mt = [];
private $w = 32;
private $n = 624;
private $m = 397;
private $f = 1812433253;
private $wMask = 0xffffffff;
// corresponds to $r = 31
private $lowerMask = 0x7fffffff;
private $upperMask = 0x80000000;
// recurrence matrix
private $a = 0x9908b0df;
// tempering
private $u = 11;
private $d = 0xffffffff;
private $s = 7;
private $b = 0x9d2c5680;
private $t = 15;
private $c = 0xefc60000;
private $l = 18;
public function __construct()
{
if (defined('HHVM_VERSION')) {
throw new RuntimeException("Pure PHP random implemnentation segfaults HHVM, so it's not available for this platform");
}
}
public function seed($seed)
{
$this->seed = $seed;
$this->index = $this->n;
$this->mt[0] = $seed & $this->wMask;
for ($i = 1; $i <= $this->n - 1; $i++) {
$this->mt[$i] = ($this->f * (
$this->mt[$i - 1] ^ (($this->mt[$i - 1] >> ($this->w - 2)) & 0b11)
) + $i) & $this->wMask;
assert($this->mt[$i] <= $this->wMask);
}
assert(count($this->mt) === 624);
return $this;
}
public function extractNumber()
{
assert($this->index <= $this->n);
if ($this->index >= $this->n) {
$this->twist();
}
$y = $this->mt[$this->index];
$y = $y ^ (($y >> $this->u) & $this->d);
assert($y <= 0xffffffff);
$y = $y ^ (($y << $this->s) & $this->b);
assert($y <= 0xffffffff);
$y = $y ^ (($y << $this->t) & $this->c);
assert($y <= 0xffffffff);
$y = $y ^ ($y >> $this->l);
assert($y <= 0xffffffff);
$this->index = $this->index + 1;
return $y & $this->wMask;
}
public function max()
{
return 0xffffffff;
}
private function twist()
{
for ($i = 0; $i <= $this->n - 1; $i++) {
$x = ($this->mt[$i] & $this->upperMask)
+ (($this->mt[($i+1) % $this->n]) & $this->lowerMask);
assert($x <= 0xffffffff);
$xA = $x >> 1;
assert($xA <= 0x7fffffff);
if (($x % 2) != 0) {
$xA = $xA ^ $this->a;
}
$this->mt[$i] = $this->mt[($i + $this->m) % $this->n] ^ $xA;
}
$this->index = 0;
}
}

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text/x-php
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Sat, May 16, 18:45 (4 h, 53 m)
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MersenneTwister.php (2 KB)

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