Levenshtein distance in PHP with multibyte support

levenshtein.php

<?php
// Levenshtein distance with multibyte support
// Improved from https://gist.github.com/santhoshtr/1710925
function mb_levenshtein($str1, $str2, $encoding = 'UTF-8', $return_lengths = false){
        $length1 = mb_strlen($str1, $encoding);
        $length2 = mb_strlen($str2, $encoding);
        if( $str1 === $str2) {
                if ($return_lengths) {
                        return array(0, $length1, $length2);
                } else {
                        return 0;
                }
        }
        if ($length1 < $length2) {
                return mb_levenshtein($str2, $str1, $encoding, $return_lengths);
        }
        if ($length1 == 0) {
                if ($return_lengths) {
                        return array(0, $length1, $length2);
                } else {
                        return $length2;
                }
        }
        $prevRow = range(0, $length2);
        $currentRow = array();
        $str1_array = mb_str_to_array($str1, $encoding);
        $str2_array = mb_str_to_array($str2, $encoding);
        for ($i = 0; $i < $length1; $i++) {
                $currentRow = array();
                $currentRow[0] = $i + 1;
                $c1 = $str1_array[$i];
                for ($j = 0; $j < $length2; $j++) {
                        $c2 = $str2_array[$j];
                        $insertions = $prevRow[$j+1] + 1;
                        $deletions = $currentRow[$j] + 1;
                        $substitutions = $prevRow[$j] + (($c1 != $c2)? 1 : 0);
                        $currentRow[] = min($insertions, $deletions, $substitutions);
                }
                $prevRow = $currentRow;
        }
        if ($return_lengths) {
                return array($prevRow[$length2], $length1, $length2);
        } else {
                return $prevRow[$length2];
        }
}

function mb_str_to_array($str, $encoding = 'UTF-8') {
        if ($encoding == 'UTF-8') {
                $array = preg_split('//u', $str, null, PREG_SPLIT_NO_EMPTY);
        } else {
                $array = array();
                for ($i = 0; $i < mb_strlen($str, $encoding); $i++) {
                        $array[] = mb_substr($str, $i, 1, $encoding);
                }
        }
        return $array;
}