Brute-force attack for php's crypt

decrypt.php

<?php

$hash = "encrypted hash";
$salt = "salt";
$digits = 8;
$thread_n = 4;

$threads = [];
for ($i = 0; $i < $thread_n; $i++) {
	$threads[$i] = new AttackThread($i, $thread_n, $hash, $salt, $digits);
	$threads[$i]->start();
}

$finished = false;
while (!$finished) {

	sleep(1);

	$finished = true;
	for ($i = 0; $i < $thread_n; $i++) {
		$finished &= !$threads[$i]->isRunning();
	}
}

echo "done\n";


class AttackThread extends Thread {
	public $id;
	public $from;
	public $to;

	private $table = ['', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'n', 'm', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];
	private $char_qty;

	private $pows = [];
	private $hash;
	private $salt;
	private $digits;

	public function __construct($id, $thread_n, $hash, $salt, $digits) {
		$this->id   = $id;
		$this->hash = $hash;
		$this->salt = $salt;
		$this->digits = $digits;

		$this->char_qty = count($this->table);

		// WORK AROUND
		$pows = [];

		for ($i = 0; $i <= $this->digits; $i++) {
			$pows[] = pow($this->char_qty, $i);
		}

		$this->pows = $pows;

		$per = intval($this->pows[$this->digits]/$thread_n);
		$this->from = $per*$this->id;
		$this->to   = $per*($this->id+1);
	}

	public function run() {
		$attempt = [];

		$count = 0;
		$per   = ($this->to - $this->from) / 100;

		echo "Thread#$this->id started From:$this->from To:$this->to\n";

		for ($i = $this->from; $i < $this->to; $i++) {
		
			if (($i - $this->from) % $per == 0) {
				echo "Thread#$this->id -- $count %\n";
				$count++;
			}
		
			for ($j = 0; $j < $this->digits; $j++) {
				$attempt[$j] = $this->table[($i / $this->pows[$j]) % $this->char_qty];
			}
		
			if (crypt(implode($attempt), $this->salt) == $this->hash) {
				echo "Thread#$this->id -- Solved: ".implode($attempt)."\n";
				exit(1);
			}
		}

		echo "Thread#$this->id finished\n";

	}
}