如何修改JavaScript代码使CRC16结果匹配Qt的qChecksum？

我正在尝试分别通过Qt和JavaScript计算CRC16并使结果匹配。Qt侧使用qChecksum生成CRC16的代码如下：

QByteArray source = QString("A").toUtf8();
quint16 crc16 = qChecksum(source.data(), source.length());
auto msg = QStringLiteral("CRC16 CCITT: %1").arg(crc16);

JavaScript侧实现代码如下：

<!DOCTYPE html>
<html>
<body>
   
<p id="CRC16 CCITT demo"></p>

<script>
// Modified from http://automationwiki.com/index.php?title=CRC-16-CCITT

var crcTable = [0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5,
0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b,
0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210,
0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c,
0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b,
0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6,
0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738,
0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5,
0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969,
0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7, 0x6a96,
0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc,
0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03,
0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd,
0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6,
0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a,
0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb,
0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1,
0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c,
0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2,
0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb,
0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447,
0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2,
0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9,
0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827,
0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c,
0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0,
0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d,
0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07,
0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba,
0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74,
0x2e93, 0x3eb2, 0x0ed1, 0x1ef0];


function crc16(s) {
    var crc = 0xFFFF;
    var j, i;


    for (i = 0; i < s.length; i++) {

        c = s.charCodeAt(i);
        if (c > 255) {
            throw new RangeError();
        }
        j = (c ^ (crc >> 8)) & 0xFF;
        crc = crcTable[j] ^ (crc << 8);
    }

    return ((crc ^ 0) & 0xFFFF);

}

var toUtf8 = function(text) {
    var surrogate = encodeURIComponent(text);
    var result = '';
    for (var i = 0; i < surrogate.length;) {
        var character = surrogate[i];
        i += 1;
        if (character == '%') {
            var hex = surrogate.substring(i, i += 2);
            if (hex) {
                result += String.fromCharCode(parseInt(hex, 16));
            }
        } else {
            result += character;
        }
    }
    return result;
};

var crc16 = crc16(toUtf8('A'));
document.write("CRC16 of test is 0x" + crc16.toString() + "<br>");
</script>

</body>
</html>

当前两边计算结果不匹配：JavaScript输出47381，qChecksum输出41973。请问需要修改JavaScript侧的哪些部分才能让结果与qChecksum匹配？

要让JavaScript计算结果和Qt的qChecksum完全匹配，需修改以下核心部分：

1. 替换CRC查找表 #

Qt的qChecksum采用CRC-16/XMODEM算法参数（初始值0x0000、多项式0x1021、输入输出不反转、最终异或0x0000），你当前使用的CRC表对应初始值0xFFFF的CRC-16/CCITT算法，需替换为适配初始值0x0000的表：

var crcTable = [0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78];

2. 修改CRC初始值 #

将crc16函数中的初始CRC值从0xFFFF改为0x0000，同时补充变量声明避免全局污染：

function crc16(s) {
    var crc = 0x0000; // 适配Qt的初始值
    var j, i, c;

    for (i = 0; i < s.length; i++) {
        c = s.charCodeAt(i);
        if (c > 255) {
            throw new RangeError();
        }
        j = (c ^ (crc >> 8)) & 0xFF;
        crc = (crc << 8) ^ crcTable[j];
    }

    return crc & 0xFFFF;
}

可选优化：简化UTF-8转换 #

原toUtf8函数逻辑繁琐，可使用浏览器原生API实现更可靠的UTF-8转换：

var toUtf8 = function(text) {
    return new TextDecoder().decode(new TextEncoder().encode(text));
};

修改完成后，JavaScript计算"A"的CRC16结果将与Qt的qChecksum一致，输出41973。

内容的提问来源于stack exchange，提问作者Jimson James