PHP实现指定时间的n月之前的这一天的两种算法

/***根据$endtime,返回指定$monthes月之前的日*/function severalMonthAgo($endtime,$monthes){if (!$endtime) {	return false;}if (!is_int($monthes) || $monthes <=0) {	return false;}$m = date("m",$endtime);$y = date("Y",$endtime);$d = date("d",$endtime);$year = floor($monthes/12);$monthes_mod = $monthes%12;if($year == 0){//<12个月	if($m < $monthes){		//当前月份小于n月前		$res_y = $y-1;		$res_m = 12-($monthes-$m);		$t = date("t",strtotime($res_y."-".$res_m."-01"));		if($d<$t){			$res_d = $d;		}else{			$res_d = $t;		}	}elseif($m == $monthes){		$res_y = $y-1;		$res_m = 12;		$t = date("t",strtotime($res_y."-".$res_m."-01"));		if($d<$t){			$res_d = $d;		}else{			$res_d = $t;		}	}elseif($m>$monthes){		$res_y = $y;		$res_m = $m-$monthes;		$t = date("t",strtotime($res_y."-".$res_m."-01"));		if($d<$t){			$res_d = $d;		}else{			$res_d = $t;		}	}}elseif($year>0){	$y = $y-$year;	$monthes = $monthes_mod;	if($m < $monthes){		//当前月份小于n月前		$res_y = $y-1;		$res_m = 12-($monthes-$m);		$t = date("t",strtotime($res_y."-".$res_m."-01"));		if($d<$t){			$res_d = $d;		}else{			$res_d = $t;		}	}elseif($m == $monthes){		$res_y = $y-1;		$res_m = 12;		$t = date("t",strtotime($res_y."-".$res_m."-01"));		if($d<$t){			$res_d = $d;		}else{			$res_d = $t;		}	}elseif($m>$monthes){		$res_y = $y;		$res_m = $m-$monthes;		$t = date("t",strtotime($res_y."-".$res_m."-01"));		if($d<$t){		$res_d = $d;		}else{			$res_d = $t;		}	}}return strtotime($res_y."-".$res_m."-".$res_d);}/***根据$endtime,返回指定$monthes月之前的日*/function severalMonthAgoEx($endtime,$monthes){if (!$endtime) {	return false;}if (!is_int($monthes) || $monthes <=0) {	return false;}$m = date("m",$endtime);$y = date("Y",$endtime);$d = date("d",$endtime);$year = floor($monthes/12);$monthes_mod = $monthes%12;$y -= $year;//$year =0或>0;//$monthes_mod =0或>0或if ($year>0) {	if ($monthes_mod>0) {		$m_diff = 12+$m-$monthes_mod;		$m_diff_div = floor($m_diff/12);		$m_diff_mod = $m_diff%12;		if ($m_diff_div > 0) {			$res_y = $y;			$res_m = $m_diff_mod;		}elseif ($m_diff_div == 0) {			$res_y = $y -1;			$res_m = $m_diff_mod;		}	}elseif ($monthes_mod==0) {		//整除		$res_y = $y;		$res_m = $m;			}}elseif ($year == 0) {	$m_diff = 12+$m-$monthes_mod;	$m_diff_div = floor($m_diff/12);	$m_diff_mod = $m_diff%12;	if ($m_diff_div > 0) {		$res_y = $y;	}elseif ($m_diff_div == 0) {		$res_y = $y -1;	}	$res_m = $m_diff_mod;}$t = date("t",strtotime($res_y."-".$res_m."-01"));if($d<$t){	$res_d = $d;}else{	$res_d = $t;}return strtotime($res_y."-".$res_m."-".$res_d);}

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