将字节流转换为数字数据类型

Let's say I have a byte-stream in which I know the location of a 64-bit value (a 64-bit nonce). The byte-order is Little-Endian. As PHP's integer data-type is limited to 32-bit (at least on 32-bit operating systems) how would I convert the byte-sequence into a PHP numeric representation (float would be sufficient I think)?Let's say I have a byte-stream in which I know