c# - 将 CRC 计算从 C# 转换为 C

Question

我目前正在使用串行监视器，以确保某些数据完整性，我正在尝试实现 CRC8 校验和，下面是我在发送消息之前对任何消息所做的计算。

public byte Checksum(params byte[] val)
{
    if (val == null)
        throw new ArgumentNullException("val");
    byte c = 0;
    foreach (byte b in val)
    {
        c = table[c ^ b];
    }
    return c;
}

我使用 0xD8 生成一个表:

public byte[] GenerateTable(CRC8_POLY polynomial)
{
    byte[] csTable = new byte[256];
    for (int i = 0; i < 256; ++i)
    {
        int curr = i;
        for (int j = 0; j < 8; ++j)
        {
            if ((curr & 0x80) != 0)
            {
            curr = (curr << 1) ^ (int)polynomial;
            }
            else
            {
                curr <<= 1;
            }
        }
        csTable[i] = (byte)curr;
    }
    return csTable;
}

这是我用来测试设置的代码:

private void btnSend_Click(object sender, EventArgs e)
{
    ProtoFrame rxFrame = new ProtoFrame();
    if (cboParam.Text == "test")
    {
        rxFrame.Start = 0x73;
        rxFrame.Size = 9;
        rxFrame.Command = 01;
        rxFrame.Unused = 0;
        rxFrame.ParamId = 0x0100;
        rxFrame.Param = 8000;
    }

    byte[] rxBuffer = getBytes(rxFrame); //call to byte array formatter
    rxBuffer[rxBuffer.Length-1] = Checksum(rxBuffer); //append crc at end of array
    ComPort.Write(rxBuffer, 0, rxBuffer.Length);
}
static byte[] getBytes(object str) //input struct
{
    int size = Marshal.SizeOf(str) + 1;
    byte[] arr = new byte[size];
    IntPtr ptr = Marshal.AllocHGlobal(size);

    Marshal.StructureToPtr(str, ptr, true);
    Marshal.Copy(ptr, arr, 0, size);
    Marshal.FreeHGlobal(ptr);

    return arr;
}

据我所知，这段代码按预期工作，我正在使用表格生成器在我的微 Controller 中实现一个硬编码表格，以加快该过程。
我不太明白的是我如何实现一个函数来以与我在这里所做的类似的方式计算 CRC。 任何正确方向的帮助或指导都是值得赞赏的。 到目前为止，我想出了这个功能:

uint8_t crc8(uint8_t *crc)
{
    uint8_t crcVal;
    int m;
    for (m = 0; m < PacketSize ;m++ )startbyte
    {
        *crc = crc8_table[(*crc) ^ m];
        *crc &= 0xFF;        
    }
}

表格在哪里:

uint8_t crc8_table[256] = {0,24,48,40,96,120,80,72,192,216,240,232,160,184,144,136,88,64,104,112,56,32,8,16,
                    152,128,168,176,248,224,200,208,176,168,128,152,208,200,224,248,112,104,64,88,16,8,
                    32,56,232,240,216,192,136,144,184,160,40,48,24,0,72,80,120,96,184,160,136,144,216,
                    192,232,240,120,96,72,80,24,0,40,48,224,248,208,200,128,152,176,168,32,56,16,8,64,
                    88,112,104,8,16,56,32,104,112,88,64,200,208,248,224,168,176,152,128,80,72,96,120,48,
                    40,0,24,144,136,160,184,240,232,192,216,168,176,152,128,200,208,248,224,104,112,88,
                    64,8,16,56,32,240,232,192,216,144,136,160,184,48,40,0,24,80,72,96,120,24,0,40,48,120,
                    96,72,80,216,192,232,240,184,160,136,144,64,88,112,104,32,56,16,8,128,152,176,168,224,
                    248,208,200,16,8,32,56,112,104,64,88,208,200,224,248,176,168,128,152,72,80,120,96,40,
                    48,24,0,136,144,184,160,232,240,216,192,160,184,144,136,192,216,240,232,96,120,80,72,
                    0,24,48,40,248,224,200,208,152,128,168,176,56,32,8,16,88,64,104,112
                    };

PacketSize 是从 rxFrame.Size 中找到的

Answer 1

因此，您只需将 C# 函数移植到 C

public byte Checksum(params byte[] val)
{
    if (val == null)
        throw new ArgumentNullException("val");
    byte c = 0;
    foreach (byte b in val)
    {
        c = table[c ^ b];
    }
    return c;
}

我。 C 中没有异常(exception)。使用返回值指示错误并添加将用作返回值的参数。由您决定是将消息长度作为参数传递还是将其保留在全局范围内:

int checksum(uint8_t const *msg, size_t msglen, uint8_t *result)

二。 foreach循环转换为for循环，其中i是索引，msg[i]是 b 来自 foreach:

int checksum(uint8_t const *msg, size_t msglen, uint8_t *result)
{
    if (msg == NULL || msglen == 0)
        return 0;

    uint8_t crc = 0;
    for (int i = 0; i < msglen; i++)
    {
        crc = table[crc ^ msg[i]];
    }

III。存储结果并返回成功代码:

int checksum(uint8_t const *msg, size_t msglen, uint8_t *result)
{
    if (msg == NULL || msglen == 0)
        return 0;

    uint8_t crc = 0;
    for (int i = 0; i < msglen; i++)
    {
        crc = table[crc ^ msg[i]];
    }

    *result = crc;
    return 1;
}

IV。用法:

uint8_t crc;
if (!checksum(message, PacketSize, &crc))
    report_error();