private function _parseCrontab($sDatetime, $sCrontab)
        {

            $aTime    = explode(' ', date('i G j n w', strtotime($sDatetime)));
            $sCrontab = explode(' ', $sCrontab);
            foreach ($sCrontab as $k => &$v) {
                $v = explode(',', $v);
                foreach ($v as &$v1) {
                    $v1 = preg_replace(array(
                                           '/^\*$/',
                                           '/^\d+$/',
                                           '/^(\d+)\-(\d+)$/',
                                           '/^\*\/(\d+)$/'
                                       ), array(
                                           'true',
                                           intval($aTime[$k]) . '===\0',
                                           '(\1<=' . intval($aTime[$k]) . ' and ' . intval($aTime[$k]) . '<=\2)',
                                           intval($aTime[$k]) . '%\1===0'
                                       ), $v1);
                }
                $v = '(' . implode(' or ', $v) . ')';
            }
            $sCrontab = implode(' and ', $sCrontab);

            return eval('return ' . $sCrontab . ';');
        }