not found anywhere crc64 based on http://bioinfadmin.cs.ucl.ac.uk/downloads/crc64/crc64.c .

(use gmp module)

<?php

/* OLDCRC */
define('POLY64REV', "d800000000000000");
define('INITIALCRC', "0000000000000000");
define('TABLELEN', 256);
/* NEWCRC */
// define('POLY64REV', "95AC9329AC4BC9B5");
// define('INITIALCRC', "FFFFFFFFFFFFFFFF");

if(function_exists('gmp_init')){
        class CRC64{

                private static $CRCTable = array();

                public static function encode($seq){

                        $crc = gmp_init(INITIALCRC, 16);
                        $init = FALSE;
                        $poly64rev = gmp_init(POLY64REV, 16);

                        if (!$init)
                        {
                                $init = TRUE;
                                for ($i = 0; $i < TABLELEN; $i++)
                                {
                                        $part = gmp_init($i, 10);
                                        for ($j = 0; $j < 8; $j++)
                                        {
                                                if (gmp_strval(gmp_and($part, "0x1")) != "0"){
                                                        // if (gmp_testbit($part, 1)){ /* PHP 5 >= 5.3.0, untested */
                                                        $part = gmp_xor(gmp_div_q($part, "2"), $poly64rev);
                                                } else {
                                                        $part = gmp_div_q($part, "2");
                                                }
                                        }
                                        self::$CRCTable[$i] = $part;
                                }
                        }

                        for($k = 0; $k < strlen($seq); $k++){
                                $tmp_gmp_val = gmp_init(ord($seq[$k]), 10);
                                $tableindex = gmp_xor(gmp_and($crc, "0xff"), $tmp_gmp_val);
                                $crc = gmp_div_q($crc, "256");
                                $crc = gmp_xor($crc, self::$CRCTable[gmp_strval($tableindex, 10)]);
                        }

                        $res = gmp_strval($crc, 16);

                        return $res;
                }
        }
} else {
        die("Please install php-gmp package!!!");
}
?>