Check dates interval function

function okdata($date1,$date2)
{
// split date into day,month,year vars with separators / or . or -. U can add more seps
	$splited1=split ('[/.-]', $date1);
	$splited2=split ('[/.-]', $date2);

	$day1=$splited1[0];
	$month1=$splited1[1];
	$year1=$splited1[2];

	$day2=$splited2[0];
	$month2=$splited2[1];
	$year2=$splited2[2];

//extract last day from given month

	$daymonth1=mktime(0,0,0,$month1+1,0,$year1);
	$daymonth2=mktime(0,0,0,$month2+1,0,$year2);


	$lastday1=strftime("%d",$daymonth1);
	$lastday2=strftime("%d",$daymonth2);

//validate last day from given month
	if ($day1>$lastday1)
	{
	$error=-1;
	$outerr.="Invalid day of month for first field!";
	}

	if ($day2>$lastday2)
	{
	$error=-1;
	$outerr.="Invalid day of month for second field!";
	}


	$mktime1=mktime (0,0,0,$month1,$day1,$year1);
	$mktime2=mktime (0,0,0,$month2,$day2,$year2);

//calculate difference between dates
	$diff=$mktime1-$mktime2;


	if ($diff<0)

	{
	$error=-1;
	$outerr.="First date cannot be greater than second date!<br>";
	}

	if ($diff==0)

	{
	$error=-1;
	$outerr.="Second date cannot be equal with first date!<br>";
	}


	if ($error==-1)
	{
	return $outerr;
	}
	else
	{
	return "Date interval succesfully validated!";
	}

}