A quick and dirty copy of a C routine for generating a CRC16-CCITT with an intial value of 0xFFFF in Javascript

CRC16-CCITT.js

// 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);

}

document.write("CRC16 of test is 0x" + crc16('test').toString(16) + "<br>");

i think this is giving wrong value

I compared to the results of an implementation in Delphi: the result is the same, so I would vote that this is giving the right value. Thanks for the code!

@rishcd There are a few variants of CRC16

I made a slight adjustment on this (working with an array, not a string) and can confirm this gives me the correct CRC.

great!

Thanks for the code. FYI, if using the buffer type in node.js , you would need to change from charCodeAt to readUInt8(). There might be a way to auto detect this.

function crc16_ccitt(s) {
    var crc = 0xFFFF;
    var j, i;
    for (i = 0; i < s.length; i++) {
        let c = s.readUInt8(i);
        if (c > 255) {
            throw new RangeError();
        }
        j = (c ^ (crc >> 8)) & 0xFF;
        crc = crcTable[j] ^ (crc << 8);
    }
    return ((crc ^ 0) & 0xFFFF);
}

Also for modbus, I was using

function crc16_modbus(buffer, start, end)
{ // based on https://github.com/yuanxu2017/modbus-crc16/blob/master/crc16.js
    var crc = 0xFFFF;
    var odd;
    if (buffer.length <= end)
      return 0;
    for (var i = start; i < end; i++) {
        crc = crc ^ buffer.readUInt8(i);
        for (var j = 0; j < 8; j++) {
            odd = crc & 0x0001;
            crc = crc >> 1;
            if (odd) {
                crc = crc ^ 0xA001;
            }
        }
    }
    return crc;
};

@chitchcock

I just wanted to thank you for this JS script.

I was searching online for a [CRC-16 XMODEM] JS script to get me thru a task and found yours, which can be modified to meet the XMODEM CRC by doing the following:

... just change var crc = 0xFFFF; to var crc = 0x0000;

NOTE: As far as I know CRC16-CCITT-FALSE(which is what the change above does) is "%100" equivalent to CRC16-XMODEM

Again: Thank you!

Thanks, working well!

In case of CRC-16/AUG-CCITT initial value should be
var crc = 0x1d0f;

// CCITT-FALSE
// var crc = 0xFFFF;
// https://crates.io/crates/crc16

If you need to pass hex (as i do )

        function crc16Hex(...s) {
                var crc = 0x1D0F;
                var j, i;
                for (let c of s) {
                    if (c > 255) {
                        throw new RangeError();
                    }
                    j = (c ^ (crc >> 8)) & 0xFF;
                    crc = crcTable[j] ^ (crc << 8);
                }
                return ((crc ^ 0) & 0xFFFF).toString(16);
            }

this works, too, with no lookup table, for buffers & strings:

export const crc16ccitt = (regInit, message) => {
  if (typeof message === 'undefined') {
    message = regInit
    regInit = 0xFFFF
  }

  if (typeof message === 'string') {
    message = message.split('').map(c => c.charCodeAt(0))
  }

  let crc = regInit + 0
  const polynomial = 0x1021

  for (const b of message) {
    for (let i = 0; i < 8; i++) {
      const bit = ((b >> (7 - i) & 1) === 1)
      const c15 = ((crc >> 15 & 1) === 1)
      crc <<= 1
      if (c15 ^ bit) crc ^= polynomial
    }
  }

  crc &= 0xffff
  return crc
}

code run success and correct, thank you.