php crc-itu

The CRC-ITU (International Telecommunication Union) algorithm is a cyclic redundancy check (CRC) algorithm that is commonly used in telecommunications systems. It is used to detect errors in data transmission by generating a checksum value that can be compared with the received data.

Here is an example of how to calculate the CRC-ITU checksum in PHP:

function crcITU($data) {
    $crc = 0xFFFF; // Initial CRC value

    for ($i = 0; $i < strlen($data); $i++) {
        $crc ^= ord($data[$i]); // XOR the CRC with the next byte of data

        for ($j = 0; $j < 8; $j++) {
            if ($crc & 0x0001) {
                $crc = ($crc >> 1) ^ 0x8408; // XOR the CRC with the polynomial value (0x8408)
            } else {
                $crc = $crc >> 1; // Shift the CRC one bit to the right
            }
        }
    }

    return $crc;
}

$data = "Hello, world!";
$crc = crcITU($data);
echo "CRC-ITU checksum: " . dechex($crc) . "\n";

This code calculates the CRC-ITU checksum for the string "Hello, world!" and prints the result in hexadecimal format. The CRC-ITU algorithm uses a polynomial value of 0x8408 and an initial CRC value of 0xFFFF. The algorithm XORs the CRC with each byte of data and performs bitwise operations to calculate the checksum value.

Note that the dechex() function is used to convert the CRC value to hexadecimal format for easier readability.