setUnsignedInt example

public function __construct($key = '')
    {
        if (self::strlen($key) < 32) {
            throw new InvalidArgumentException(
                'Poly1305 requires a 32-byte key'
            );
        }
        /* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
        $this->r = array(
            // st->r[0] = ...             ParagonIE_Sodium_Core32_Int32::fromReverseString(self::substr($key, 0, 4))
                ->setUnsignedInt(true)
                ->mask(0x3ffffff),
            // st->r[1] = ...             ParagonIE_Sodium_Core32_Int32::fromReverseString(self::substr($key, 3, 4))
                ->setUnsignedInt(true)
                ->shiftRight(2)
                ->mask(0x3ffff03),
            // st->r[2] = ...             ParagonIE_Sodium_Core32_Int32::fromReverseString(self::substr($key, 6, 4))
                ->setUnsignedInt(true)
                ->shiftRight(4)
                ->mask(0x3ffc0ff),