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

I was able to produce the same checksum with implementation like below:

define('CRC16POLYN', 0x1021);

function CRC16Normal($buffer) {
    $result = 0xFFFF;
    if (($length = strlen($buffer)) > 0) {
        for ($offset = 0; $offset < $length; $offset++) {
            $result ^= (ord($buffer[$offset]) << 8);
            for ($bitwise = 0; $bitwise < 8; $bitwise++) {
                if (($result <<= 1) & 0x10000) $result ^= CRC16POLYN;
                $result &= 0xFFFF;
            }
        }
    }
    return $result;
}

echo dechex(CRC16Normal(hex2bin('100000000000000012510908001800040214000c000c021c0002000000000000')));

Above gives a077 on output.

Code snippet found on https://forums.digitalpoint.com/threads/php-define-function-calculate-crc-16-ccitt.2584389/