c# - CRC16 ISO 13239 实现

Question

我正尝试在 C# 中实现 Crc16。我已经尝试过许多不同的实现，但其中大多数都给了我不同的值。以下是我已经使用过的一些代码。

    private static int POLYNOMIAL = 0x8408;
    private static int PRESET_VALUE = 0xFFFF;

    public static int crc16(byte[] data)
    {
        int current_crc_value = PRESET_VALUE;
        for (int i = 0; i < data.Length; i++)
        {
            current_crc_value ^= data[i] & 0xFF;
            for (int j = 0; j < 8; j++)
            {
                if ((current_crc_value & 1) != 0)
                {
                    current_crc_value = (current_crc_value >> 1) ^ POLYNOMIAL;
                }
                else
                {
                    current_crc_value = current_crc_value >> 1;
                }
            }
        }
        current_crc_value = ~current_crc_value;

        return current_crc_value & 0xFFFF;
    }

这是我使用的另一个实现，但都给出了不同的值

    const ushort polynomial = 0xA001;
    ushort[] table = new ushort[256];

    public ushort ComputeChecksum(byte[] bytes)
    {
        ushort crc = 0;
        for (int i = 0; i < bytes.Length; ++i)
        {
            byte index = (byte)(crc ^ bytes[i]);
            crc = (ushort)((crc >> 8) ^ table[index]);
        }
        return crc;
    }

    public byte[] ComputeChecksumBytes(byte[] bytes)
    {
        ushort crc = ComputeChecksum(bytes);
        return BitConverter.GetBytes(crc);
    }

    public Crc16()
    {
        ushort value;
        ushort temp;
        for (ushort i = 0; i < table.Length; ++i)
        {
            value = 0;
            temp = i;
            for (byte j = 0; j < 8; ++j)
            {
                if (((value ^ temp) & 0x0001) != 0)
                {
                    value = (ushort)((value >> 1) ^ polynomial);
                }
                else
                {
                    value >>= 1;
                }
                temp >>= 1;
            }
            table[i] = value;
        }
    }

我使用的值是一个Octet String "[jp3]TEST [fl]Flashing[/fl]" 及其预期值为十六进制的 95F9。这是NTCIP协议(protocol)指南上的例子

谢谢

Answer 1

这个:

static readonly ushort[] fcstab = new ushort[] { 
    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 
    0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 
    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 
    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 
    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 
    0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5, 
    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 
    0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974, 
    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, 
    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 
    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 
    0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 
    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 
    0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 
    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 
    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70, 
    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 
    0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff, 
    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 
    0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 
    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 
    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 
    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 
    0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 
    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 
    0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, 
    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 
    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 
    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 
    0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 
    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 
    0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 
};

static ushort compute_fcs(byte[] data)
{
    return compute_fcs(data, 0, data.Length);
}

static ushort compute_fcs(byte[] data, int start, int length)
{
    ushort fcs = 0xFFFF;

    int end = start + length;

    for (int i = start; i < end; i++)
    {
        fcs = (ushort)(((ushort)(fcs >> 8)) ^ fcstab[(fcs ^ data[i]) & 0xFF]);
    }

    return (ushort)(~fcs);
}

static void Main(string[] args)
{
    byte[] pattern = new byte[] { 0x02, 0x07, 0x01, 0x03, 0x01, 0x02, 0x00, 0x34, 0x07, 0x07, 0x1C, 0x59, 0x34, 0x6F, 0xE1, 0x83, 0x00, 0x00, 0x41, 0x06, 0x06, 0x7B, 0x3C, 0xFF, 0xCF, 0x3C, 0xC0 };

    // http://www.ite.org/standards/1203v03-04%20Part%201%20dms2011.pdf
    // Page 158, CRC = 0x52ED
    ushort fcs = compute_fcs(pattern); // 0x52ED
}

将用于此处给出的唯一测试 http://www.ite.org/standards/1203v03-04%20Part%201%20dms2011.pdf (大约第 158 页，CRC = 0x52ED)。

对于 PDF 的字符串示例，如后几页所写:

" Indicates the CRC-16 (polynomial defined in ISO/IEC 3309) value created using the values of the dmsMessageMultiString (MULTI-Message), the dmsMessageBeacon, and the dmsMessagePixelService objects in the order listed, not including the OER type or length fields. Note that the calculation shall assume a value of zero (0) for the dmsMessageBeacon object and/or for the dmsMessagePixelService object if they are not supported

(强调)

所以:

string str = "[jp3]TEST [fl]Flashing[/fl]";
var bytes = Encoding.ASCII.GetBytes(str);
Array.Resize(ref bytes, bytes.Length + 2);

// Note that these two rows are useless, because the Array.Resize will have already filled with 0
bytes[bytes.Length - 2] = 0; // dmsMessageBeacon
bytes[bytes.Length - 1] = 0; // dmsMessagePixelService 

ushort fcs2 = compute_fcs(bytes); // 0xF995
var bytes2 = BitConverter.GetBytes(fcs2); // 0x95 0xF9

这表明该协议(protocol)是小字节序的(因为我的 PC 是 Intel 的)。实际上字符串的 CRC-16 是 0xF995，但是这 16 位在内存中显示为 0x95 0xF9(如示例中所示，显示单个字节)。