Reference this program :
$aa=3123456789;
$bb = $aa % 1000000000;
echo "$aa,$bb<br>\n";
$aa=3123456789;
$cc = $aa - floor($aa/1000000000)*1000000000;
echo "$aa,$cc<br>\n";

The result like the following :
3123456789,-147483648
3123456789,123456789

Because $aa is a bigint, so $bb will return a negative,
but the $cc is a normal result.