CRC 校验算法

--- 计算 hj212 CRC
--- @param str string 212 字符串
--- @return string 四位crc校验值
local function crcCal(str)
    local crcReg = 0xFFFF
    for i = 1, str:len() do
        crcReg = bit.bxor(bit.rshift(crcReg, 8), string.byte(str, i))
        for j = 1, 8 do
            local check = bit.band(crcReg, 0x0001)
            crcReg = bit.rshift(crcReg, 1)
            if check == 0x0001 then crcReg = bit.bxor(crcReg, 0xA001) end
        end
    end
    return string.format("%04X", crcReg)
end