Easy substr for paragraph in PHP

substr_paragraph.php

<?php 

	function substr_paragraph($string, $length = 520, $html = false) {

		$pos = strpos($string, "</p>",$length);
		$tag_len = 4;

		if(empty($pos)){
			$pos = strpos($string, "</div>",$length);
		  	$tag_len = 5;
		}

		if(empty($pos)){
			// No usable html found
			$pos = $length-$tag_len;
		}
	
	    	$string = substr($string,0, $pos+$tag_len);
	
		if($html != true){
			 $string = strip_tags($string);
		}
	
		  return $string;

	}