ParagonIE_Sodium_Core32_Int64::mask64

    public function mask64($hi = 0, $lo = 0)
    {
        /** @var int $a */
        $a = ($hi >> 16) & 0xffff;
        /** @var int $b */
        $b = ($hi) & 0xffff;
        /** @var int $c */
        $c = ($lo >> 16) & 0xffff;
        /** @var int $d */
        $d = ($lo & 0xffff);
        return new ParagonIE_Sodium_Core32_Int64(
            array(
                $this->limbs[0] & $a,
                $this->limbs[1] & $b,
                $this->limbs[2] & $c,
                $this->limbs[3] & $d
            ),
            $this->unsignedInt
        );
    }