CRC16-CCITT计算

Question

这是代码

func crc16ccitt(data: [UInt8],seed: UInt16 = 0x1d0f, final: UInt16 = 0xffff)->UInt16{
    var crc = final
    data.forEach { (byte) in
        crc ^= UInt16(byte) << 8
        (0..<8).forEach({ _ in
            if (crc & UInt16(0x8000)) != 0 {
                crc = (crc << 1) ^ 0x1021
            }
            else {
                crc = crc << 1
            }
        })
    }
    return UInt16(crc)
}

更新的答案

func crc16ccitt(data: [UInt8],seed: UInt16 = 0x1d0f, final: UInt16 = 0xffff) -> UInt16{
    var crc = final
    data.forEach { (byte) in
        crc ^= UInt16(byte) << 8
        (0..<8).forEach({ _ in
            if (crc & UInt16(0x8000)) != 0 {
                crc = (crc << 1) ^ 0x1021
            }
            else {
                crc = crc << 1
            }
            //crc = (crc & UInt16(0x8000)) != 0 ? (crc << 1) ^ 0x1021 : crc << 1
        })
    }
    return UInt16(crc ^ final)
}

Answer 1

CRC的初始化应该是

var crc = final

《儿童权利公约》的更新应该是

    crc ^= UInt16(byte) << 8

通过这些更改，代码将为输入0xaa生成校验和0xf550。请注意，0xF550应该是0x0AAF，位顺序相反，因此这是计算中缺少的步骤。

func crc16ccitt_false() -> UInt16 {
    return crc16(data_order: straight_8, remainder_order: reverse_16, remainder: 0xffff, polynomial: 0x1021)
}

let tData = Data([0xAA])
print(String(format: "crc16ccitt_false:  %04X", tData.crc16ccitt_false())) // 0AAF