This function is defined in ~/libxorp/selector.cc:117 as inline bool SelectorList::Node::is_empty() { return (_mask[SEL_RD_IDX] == _mask[SEL_WR_IDX] == _mask[SEL_EX_IDX] == 0); } Shoudn't the return statement be return (_mask[SEL_RD_IDX] == 0 && _mask[SEL_WR_IDX] == 0 && _mask[SEL_EX_IDX] == 0); because i. e. 0 == 1 == 2 == 0 returns true, too? Regards, Mark.