这是bug吗？该如何处理

function my_bcmod( $x, $y ) {
    $take = 5;
    $mod = '';
    do{
        $a = (int)$mod.substr( $x, 0, $take );
        $x = substr( $x, $take );
        $mod = $a % $y;
		echo $a.'-'.$x.'-'.$mod.'
';
    }
    while ( strlen($x) ); 
    return (int)$mod; 
}

echo my_bcmod( "7044060001970316212900", 150 );//50

/*
070440-60001970316212900-90
9060001-970316212900-1
197031-6212900-81
8162129-00-29
2900--50
*/