php中的时间函数DateDiff和DateAdd

<?php
function DateDiff($part, $begin, $end)
{
 $diff = strtotime($end) - strtotime($begin);
 switch($part)
 {
  case "y": $retval = bcdiv($diff, (60 * 60 * 24 * 365)); break;
  case "m": $retval = bcdiv($diff, (60 * 60 * 24 * 30)); break;
  case "w": $retval = bcdiv($diff, (60 * 60 * 24 * 7)); break;
  case "d": $retval = bcdiv($diff, (60 * 60 * 24)); break;
  case "h": $retval = bcdiv($diff, (60 * 60)); break;
  case "n": $retval = bcdiv($diff, 60); break;
  case "s": $retval = $diff; break;
 }
 return $retval;
}

function DateAdd($part, $number, $date)
{
 $date_array = getdate(strtotime($date));
 $hor = $date_array["hours"];
 $min = $date_array["minutes"];
 $sec = $date_array["seconds"];
 $mon = $date_array["mon"];
 $day = $date_array["mday"];
 $yar = $date_array["year"];
 switch($part)
 {
  case "y": $yar += $number; break;
  case "q": $mon += ($number * 3); break;
  case "m": $mon += $number; break;
  case "w": $day += ($number * 7); break;
  case "d": $day += $number; break;
  case "h": $hor += $number; break;
  case "n": $min += $number; break;
  case "s": $sec += $number; break;
 }
 return date("Y-m-d H:i:s", mktime($hor, $min, $sec, $mon, $day, $yar));
}

Function DateAdd($part, $n, $date)
{
 switch($part)
 {
  case "y": $val = date("Y-m-d H:i:s", strtotime($date ." +$n year")); break;
  case "m": $val = date("Y-m-d H:i:s", strtotime($date ." +$n month")); break;
  case "w": $val = date("Y-m-d H:i:s", strtotime($date ." +$n week")); break;
  case "d": $val = date("Y-m-d H:i:s", strtotime($date ." +$n day")); break;
  case "h": $val = date("Y-m-d H:i:s", strtotime($date ." +$n hour")); break;
  case "n": $val = date("Y-m-d H:i:s", strtotime($date ." +$n minute")); break;
  case "s": $val = date("Y-m-d H:i:s", strtotime($date ." +$n second")); break;
 }
 return $val;
}
?>