Support for 5 param signature in levenshtein

This fixes issue locutusjs#166
The implementation is direct port of PHP's source code (except for param handling)

Author: kukawski

functions/strings/levenshtein.js

@@ -1,25 +1,42 @@
-function levenshtein(s1, s2) {
+function levenshtein(s1, s2, cost_ins, cost_rep, cost_del) {
   //       discuss at: http://phpjs.org/functions/levenshtein/
   //      original by: Carlos R. L. Rodrigues (http://www.jsfromhell.com)
   //      bugfixed by: Onno Marsman
   //       revised by: Andrea Giammarchi (http://webreflection.blogspot.com)
   // reimplemented by: Brett Zamir (http://brett-zamir.me)
   // reimplemented by: Alexander M Beedie
+  // reimplemented by: Rafał Kukawski
   //        example 1: levenshtein('Kevin van Zonneveld', 'Kevin van Sommeveld');
   //        returns 1: 3
+  //        example 2: levenshtein("carrrot", "carrots");
+  //        returns 2: 2
+  //        example 3: levenshtein("carrrot", "carrots", 2, 3, 4);
+  //        returns 3: 6
+  
+  var LEVENSHTEIN_MAX_LENGTH = 255; // PHP limits the function to max 255 character-long strings
+  
+  cost_ins = cost_ins == null ? 1 : +cost_ins;
+  cost_rep = cost_rep == null ? 1 : +cost_rep;
+  cost_del = cost_del == null ? 1 : +cost_del;
 
   if (s1 == s2) {
     return 0;
   }
 
-  var s1_len = s1.length;
-  var s2_len = s2.length;
-  if (s1_len === 0) {
-    return s2_len;
+  var l1 = s1.length;
+  var l2 = s2.length;
+  
+  if (l1 === 0) {
+    return l2 * cost_ins;
   }
-  if (s2_len === 0) {
-    return s1_len;
+  if (l2 === 0) {
+    return l1 * cost_del;
   }
+  
+  // Enable the 3 lines below to set the same limits on string length as PHP does
+  /*if (l1 > LEVENSHTEIN_MAX_LENGTH || l2 > LEVENSHTEIN_MAX_LENGTH) {
+    return -1;
+  }*/
 
   // BEGIN STATIC
   var split = false;
@@ -35,38 +52,41 @@ function levenshtein(s1, s2) {
     s2 = s2.split('');
   }
 
-  var v0 = new Array(s1_len + 1);
-  var v1 = new Array(s1_len + 1);
+  var p1 = new Array(l2 + 1);
+  var p2 = new Array(l2 + 1);
 
-  var s1_idx = 0,
-    s2_idx = 0,
-    cost = 0;
-  for (s1_idx = 0; s1_idx < s1_len + 1; s1_idx++) {
-    v0[s1_idx] = s1_idx;
+  var i1, i2, c0, c1, c2, tmp;
+  
+  for (i2 = 0; i2 <= l2; i2++) {
+    p1[i2] = i2 * cost_ins;
   }
-  var char_s1 = '',
-    char_s2 = '';
-  for (s2_idx = 1; s2_idx <= s2_len; s2_idx++) {
-    v1[0] = s2_idx;
-    char_s2 = s2[s2_idx - 1];
-
-    for (s1_idx = 0; s1_idx < s1_len; s1_idx++) {
-      char_s1 = s1[s1_idx];
-      cost = (char_s1 == char_s2) ? 0 : 1;
-      var m_min = v0[s1_idx + 1] + 1;
-      var b = v1[s1_idx] + 1;
-      var c = v0[s1_idx] + cost;
-      if (b < m_min) {
-        m_min = b;
+  
+  for (i1 = 0; i1 < l1 ; i1++) {
+    p2[0] = p1[0] + cost_del;
+    
+    for (i2 = 0; i2 < l2; i2++) {
+      c0 = p1[i2] + ((s1[i1] == s2[i2]) ? 0 : cost_rep);
+      c1 = p1[i2 + 1] + cost_del;
+      
+      if (c1 < c0) {
+        c0 = c1;
       }
-      if (c < m_min) {
-        m_min = c;
+      
+      c2 = p2[i2] + cost_ins;
+      
+      if (c2 < c0) {
+        c0 = c2;
       }
-      v1[s1_idx + 1] = m_min;
+      
+      p2[i2 + 1] = c0;
     }
-    var v_tmp = v0;
-    v0 = v1;
-    v1 = v_tmp;
+    
+    tmp = p1;
+    p1 = p2;
+    p2 = tmp;
   }
-  return v0[s1_len];
-}
+  
+  c0 = p1[l2];
+  
+  return c0;
+}