/**
  * 程序执行时间
  *
  * @return  int 单位ms
  */
 function execute_time() {
     $stime = explode ( ' ', SYS_START_TIME );
     $etime = explode ( ' ', microtime () );
     return number_format ( ($etime [1] + $etime [0] - $stime [1] - $stime [0]), 6 );
 }