buffer = new Buffer [0xAA,0xBB, 0xAA,0xBB,0xCC,0xDD]
big =
Buffer::pos = -1
Buffer::unpack = (struct) ->
    packet = {}
    for field of struct
        val = 0
        for i in [struct[field].size-1..0]
            val|=(@[@pos+=1]<<(i<<3))
        packet[field] =
            if not struct[field].signed or not struct[field].signed?
                val &((1<<(struct[field].size<<2))-1)
            else (((~val&((1<<(struct[field].size<<2))-1))+1)*-1)
    packet


packet = buffer.unpack
    itemID      : (size:2)
    interfaceID : (size:4)

console.log packet.itemID.toString 16
console.log packet.interfaceID.toString 16