/** 获取当前时间戳，精确到毫秒 */
function microtime_float()
{
list($usec, $sec) = explode(" ", microtime());
return ((float)$usec + (float)$sec);
}
/** 格式化时间戳，精确到毫秒，x代表毫秒 */
function microtime_format($tag, $time)
{
list($usec, $sec) = explode(".", $time);
$date = date($tag,$usec);
return str_replace('x', $sec, $date);
}