the first example shifted by the positive number and the result is 4, but the second example shifted by the negative number and the result is ArithmeticError(this example is the same for left shift)
<?php
$shif =1;
$number = 8;
$result = $number >> $shif;
echo $result; //// 1000 >> 01000 = 4
$shif =-1;
$number = 8;
$result = $number >> $shif;
////result is ArithmeticError
?>