Working with big integer values in ZF2

Code
<?php

use Zend\Math\BigInteger\BigInteger;

$i 100000000000000000000 1;
var_dump($i);

$bcmath BigInteger::factory('Gmp');
$i $bcmath->add('100000000000000000000''1');
var_dump($i);
Result
float(1.0E+20)
string(21) "100000000000000000001"
Used Versions
PHP 7.1, Zend 3.0, Symfony 3.2, Laravel 5.2, PHPUnit 5.6, Doctrine 2.6