pocketmine\entity\Human::getLevelFromXp PHP Method

    public static function getLevelFromXp(int $xp) : array
    {
        $xp &= 0x7fffffff;
        /** These values are correct up to and including level 16 */
        $a = 1;
        $b = 6;
        $c = -$xp;
        if ($xp > self::getTotalXpRequirement(16)) {
            /** Modify the coefficients to fit the relevant equation */
            if ($xp <= self::getTotalXpRequirement(31)) {
                /** Levels 16-31 */
                $a = 2.5;
                $b = -40.5;
                $c += 360;
            } else {
                /** Level 32+ */
                $a = 4.5;
                $b = -162.5;
                $c += 2220;
            }
        }
        $answer = max(Math::solveQuadratic($a, $b, $c));
        //Use largest result value
        $level = floor($answer);
        $progress = $answer - $level;
        return [$level, $progress];
    }