/* 
| @param char|int $start_date 一个有效的日期格式，例如：20091016，2009-10-16 
| @param char|int $end_date 同上 
| @return 给定日期之间的周末天数 
*/ 
function get_weekend_days($start_date,$end_date){ 

if (strtotime($start_date) > strtotime($end_date)) list($start_date, $end_date) = array($end_date, $start_date); 

$start_reduce = $end_add = 0; 

$start_N = date('N',strtotime($start_date)); 
$start_reduce = ($start_N == 7) ? 1 : 0; 

$end_N = date('N',strtotime($end_date)); 
in_array($end_N,array(6,7)) && $end_add = ($end_N == 7) ? 2 : 1; 

$days = abs(strtotime($end_date) - strtotime($start_date))/86400 + 1; 

return floor(($days + $start_N - 1 - $end_N) / 7) * 2 - $start_reduce + $end_add; 
}