Implementation crc64() in php 64bit

<?php

/**
 * @return array
 */
function crc64Table()
{
    $crc64tab = [];

    // ECMA polynomial
    $poly64rev = (0xC96C5795 << 32) | 0xD7870F42;

    // ISO polynomial
    // $poly64rev = (0xD8 << 56);

    for ($i = 0; $i < 256; $i++)
    {
        for ($part = $i, $bit = 0; $bit < 8; $bit++) {
            if ($part & 1) {
                $part = (($part >> 1) & ~(0x8 << 60)) ^ $poly64rev;
            } else {
                $part = ($part >> 1) & ~(0x8 << 60);
            }
        }

       $crc64tab[$i] = $part;
    }

    return $crc64tab;
}

/**
 * @param string $string
 * @param string $format
 * @return mixed
 * 
 * Formats:
 *  crc64('php'); // afe4e823e7cef190
 *  crc64('php', '0x%x'); // 0xafe4e823e7cef190
 *  crc64('php', '0x%X'); // 0xAFE4E823E7CEF190
 *  crc64('php', '%d'); // -5772233581471534704 signed int
 *  crc64('php', '%u'); // 12674510492238016912 unsigned int
 */
function crc64($string, $format = '%x')
{
    static $crc64tab;

    if ($crc64tab === null) {
        $crc64tab = crc64Table();
    }

    $crc = 0;

    for ($i = 0; $i < strlen($string); $i++) {
        $crc = $crc64tab[($crc ^ ord($string[$i])) & 0xff] ^ (($crc >> 8) & ~(0xff << 56));
    }

    return sprintf($format, $crc);
}