javascript - 需要帮助纠正用 Javascript (node.js) 编写的 CRC-ITU 检查方法中的问题

Question

我们正尝试在 Javascript 上编写 GPS 设备监听器。

在执行此操作时，我们无法为 CRC-ITU 错误检查开发正确的脚本。从协议(protocol)文档生成crc码的解释如下

A check code may be used by the terminal or the server to distinguish whether the received information is error or not. To prevent errors occur during data transmission, error check is added to against data misoperation, so as to increase the security and efficiency of the system. The check code is generated by the CRC-ITU checking method. The check codes of data in the structure of the protocol, from the Packet Length to the Information Serial Number (including “Packet Length” and “Information Serial Number”) , are values of CRC-ITU. CRC error occur when the received information is calculated, the receiver will ignore and discard the data packet.

我们引用了协议(protocol)文档中给出的C代码示例-

// calculate the 16-bit CRC of data with predetermined length. 

U16 GetCrc16(const U8* pData, int nLength) 
{ 
   U16 fcs = 0xffff; // initialization 
   while(nLength>0)
   { 
     fcs = (fcs >> 8) ^ crctab16[(fcs ^ *pData) & 0xff]; 
     nLength--; 
     pData++; 
   } 
   return ~fcs; // negated 
}

数组 crctab16 与我们的代码示例中提到的数组相同

    Incoming data string comes in following format

    Example of data packet sent by the terminal 78 78 0D 01 01 23 45 67 89 01 23 45 00 01 8C DD 0D 0A

    Explanation

    Start Bit - 0x78 0x78
    Length - 0x0D
    Protocol - 0x01
    Terminal ID - 0x01 0x23 0x45 0x67 0x89 0x01 0x23 0x45
    Serial No - 0x00 0x01
    Error - 0x8C 0xDD
    Stop Bit - 0x0D 0x0A

下面是我们的 Javascript 代码

var net = require('net');

net.createServer(function(socket) 
{

    socket.setEncoding('hex');

    // New client connection event
    socket.on('connect', function(data)

    // Incoming data event
    socket.on('data', function(data) 
    {
        console.log("Client said: " + data); // server log
        data_p = data.substring(4,28);
        err_code = crc16(data_p);
        console.log("error: " + err_code);
    });


    // Disconnect event
    socket.on('end', function()
    {
        //Log it to the server output
        console.log("someone left us." + socket.remoteAddress);
    });

}).listen(3006);

console.log("TCP ECHO SERVER STARTED ON 3006");





function crc16(buf)
{

    var crcTable = 
    [
        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
    ];


    crcX = parseInt("FFFF",16);
    cr1 = parseInt("FF",16);
    cr2 = parseInt("FFFF",16);
    i = 0;

    while(i < buf.length)
    {
        str = buf.substring(i,i+4);
        console.log("str "+str);
        str_hex = parseInt(str,16);

        j = (crcX ^ str_hex) & cr1;
        crcX = (crcX >> 8) ^ crcTable[j] ;

        i = i + 4;
    }

    crcX = ~crcX;

    console.log("crcX - " + crcX.toString(16));
    return crcX;
}

请在下面找到输入字符串对和应该由函数 crc16 生成的相应代码

    78780d01035889905017664600267bf90d0a - 7bf9
    78780d010358899050176646002ab1950d0a - b195
    78780d010358899050176646002ba01c0d0a - a01c

请帮助我们找出代码中的错误。

非常感谢。

Answer 1

原始代码中的 ~ 之所以有效，是因为它是 16 位类型。您应该使用 crcX = crcX ^ 0xffff 而不是 crcX = ~crcX。

您的 buf.substring(i,i+4) 和 i = i + 4 也是错误的。您需要一次处理一个字节，即两个十六进制数字。它们都应该是 i+2。