Function UUID v4

    function UUIDv4() {
       return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',

         // 32 bits for "time_low"
         mt_rand(0, 0xffff), mt_rand(0, 0xffff),

         // 16 bits for "time_mid"
         mt_rand(0, 0xffff),

         // 16 bits for "time_hi_and_version",
         // four most significant bits holds version number 4
         mt_rand(0, 0x0fff) | 0x4000,

         // 16 bits, 8 bits for "clk_seq_hi_res",
         // 8 bits for "clk_seq_low",
         // two most significant bits holds zero and one for variant DCE1.1
         mt_rand(0, 0x3fff) | 0x8000,

         // 48 bits for "node"
         mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
       );
     }