php pack 用一个string 保存一个double 的数组

$total = 10;
$double = "";
for ($i = 0; $i < $total; $i++)
{
$double .= pack("d", $i + 0.3);

}

for ($i = 0; $i < $total; $i++)
{
$res = unpack("@" . ($i * 8) . "/d", $double);
//$res = unpack("@" . ($i * 8) . "/d"."*{$i}", $double);
var_dump($res);die;
}