Search and replace words (using random characters) contained in a text, using blacklists - Optimized version

Search and replace words with blacklist - v2

<?php

	/**
	 *	Search and replace words with blacklist - v. 0.2
	 *	------------------------------------------------------------
	 *	Optimized version - Thanks to my friend:
	 *	Flavio 'darkjoker' Giobergia - https://github.com/darkjoker
	 *	------------------------------------------------------------
	 *
	 *	The generation of random characters, has been eliminated, to make
	 *	the script faster and more functional, and possibly to make the
	 *	text fit in case of checksum on the text (for example: a file
	 *	contained in an archive)
	 *
	 *	------------------------------------------------------------
	 *
	 *	@param String $text_to_check - Text to be analyzed and eventually to be replace
	 *	@param Array $blacklist_words - List of words to be find and replace
	 */

	$text_to_check = "Lorem ipsum DOLOR Bullshit";
	$blacklist_words = array("God", "em", "shit", "pig");

	function filtro($str) {
		global $blacklist_words;
		foreach ($blacklist_words as $w) {
			$len = strlen($w);
			$new = $w[0].str_repeat("*",$len-2).$w[$len-1];
			$str = str_ireplace($w,$new,$str);
		}
		return $str;
	}

	echo filtro($text_to_check);