How to calculate CRC16 CCITT in PHP HEX?

Question

I\'m trying to use a PHP CRC16 CCITT function to calculate the checksum.

A device sends me a PACKET with Checksum included:

10 00 00 00 00 00

Answer 1

So I was looking for how to calculate checksum according to [ISO/IEC 13239] using the polynomial '1021' (hex) and initial value 'FFFF' (hex). I found this link which can calculate many types of CRC. After submitting my input, I wanted the value of the field CRC-CCITT (0xFFFF), which is something like this:

So I took the JS function (in the .js file, the function name is CRCFFFF ) that calculated the CCITT, and created the PHP version of it.

function crcChecksum($str) {
    // The PHP version of the JS str.charCodeAt(i)
    function charCodeAt($str, $i) {
        return ord(substr($str, $i, 1));
    }

    $crc = 0xFFFF;
    $strlen = strlen($str);
    for($c = 0; $c < $strlen; $c++) {
        $crc ^= charCodeAt($str, $c) << 8;
        for($i = 0; $i < 8; $i++) {
            if($crc & 0x8000) {
                $crc = ($crc << 1) ^ 0x1021;
            } else {
                $crc = $crc << 1;
            }
        }
    }
    $hex = $crc & 0xFFFF;
    $hex = dechex($hex);
    $hex = strtoupper($hex);

    return $hex;
}

$result = crcChecksum('replace with your string here');// In my case, this gave me the desired output, which is '627B' (without '0x')

In case you need the '0x', just add it:

$result = '0x' . crcChecksum('replace with your string here');// result = '0x627B'