Php MersenneTwister implementation without global state.

MersenneTwister.php

<?php

/**
 * Class BS_MersenneTwister
 * implements MT 19937
 */
class BS_MersenneTwister 
{
	private $seed=null; // Seed
	
	private $r = 0; // number of reseeds
	private $mti=0; // The index to use when selecting a number to randomize
	private $mt=array(); // 624 element array used to get random numbers
	
	const N = 624; /* degree of recurrence */
	const M = 397; /* number of parallel sequences */
	const UPPER_MASK = 0x80000000; /* most significant w-r bits */
	const LOWER_MASK = 0x7fffffff; /* least significant r bits */
	
	const MERSENNE_PRIME = 0x6c078965; /* mersenne prime number */
	const MATRIX_A = 0x9908b0df;   /* constant vector a */
	const TEMPERING_B = 0x9d2c5680; /* tempering bitmasks */
	const TEMPERING_C = 0xefc60000; /* tempering bitmasks */
	const TEMPERING_S = 7; /* tempering bit shift */
	const TEMPERING_T = 15; /* tempering bit shift */
	const TEMPERING_U = 11; /* mt tempering bit shift */
	const TEMPERING_L = 18; /* mt tempering bit shift */
	
	const MASK14 = 0x3FFF;
	const MASK21 = 0x1FFFFF;
	const MASK31 = 0x7FFFFFFF;
	const MASK32 = 0xFFFFFFFF;
	
	public function __construct($seed, $index=0)
	{
		if($index < 0) {
			throw new Exception('The generator can not be initialized with a index below 0.');
		}
		
		if($seed === null) {
			throw new Exception('The generator needs a valid (int)seed to be initialized.');
		}
		
		$this->seed = $seed;
		$this->mti = self::N + $index;
		$this->mt = array(0 => &$seed, self::N => &$seed);

		for($i = 1; $i < self::N; ++$i) {
			$this->mt[$i] = (self::MERSENNE_PRIME * ($this->mt[$i - 1] ^ ($this->mt[$i - 1] >> 30)) + $i) & self::MASK32;
		}
	}

	private function _reseed() 
	{
		static $mag01 = array(0, self::MATRIX_A);

		$mt = &$this->mt;
		$mti = &$this->mti;

		/* generate 0 to 226 */
		for ($kk=0;$kk<self::N-self::M;$kk++) {
			$y = ($mt[$kk]&self::UPPER_MASK)|($mt[$kk+1]&self::LOWER_MASK);
			$mt[$kk] = $mt[$kk+self::M] ^ (($y >> 1) & self::MASK31) ^ $mag01[$y & 1];
		}
		/* generate 227 to 622 */
		for (;$kk<self::N-1;$kk++) {
			$y = ($mt[$kk]&self::UPPER_MASK)|($mt[$kk+1]&self::LOWER_MASK);
			$mt[$kk] = $mt[$kk+(self::M-self::N)] ^ (($y >> 1) & self::MASK31) ^ $mag01[$y & 1];
		}
		/* generate 623 */
		$y = ($mt[self::N-1]&self::UPPER_MASK)|($mt[0]&self::LOWER_MASK);
		$mt[self::N-1] = $mt[self::M-1] ^ (($y >> 1) & self::MASK31) ^ $mag01[$y & 1];

		$mti -= self::N;
		$this->r++;
	}

	private function _clamp($min, $x, $max)
	{
		return max($min, min($max, $x));
	}

	private function _mapIntoRange($src_min, $src_max, $src, $dst_min, $dst_max)
	{
		if ($src_max - $src_min <= 0.0000001) return $dst_min;
		$r = ($this->_clamp($src_min, $src, $src_max) - $src_min) / ($src_max - $src_min);
		return $dst_min + ($dst_max - $dst_min) * $r;
	}
	
	private function _checkRange($min, $max) 
	{
		if($min > $max) {
			throw new Exception('MIN can not be bigger than MAX in a random Range');
		}
	}
	
	public function int32() {
		$mt = &$this->mt;
		$mti = &$this->mti;
		
		while($mti >= self::N) {
			$this->_reseed();
		}

		$y = $mt[$mti++];

		/* Tempering */
		$y ^= ($y >> self::TEMPERING_U) & self::MASK21;
		$y ^= ($y << self::TEMPERING_S) & self::TEMPERING_B;
		$y ^= ($y << self::TEMPERING_T) & self::TEMPERING_C;
		$y ^= ($y >> self::TEMPERING_L) & self::MASK14;

		return $y;
	}

	public function int($min, $max)
	{
		$this->_checkRange($min, $max);
		return $this->int32() % ($max - $min + 1) + $min;
	}

	public function float($min=0, $max=1)
	{
		$this->_checkRange($min, $max);
		$f = $this->int32() / self::MASK32;
		return $this->_mapIntoRange(0,1,$f,$min,$max);
	}
}