Improve performance of Array.prototype.join and String.prototype.substring...

src/string.js

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 487 matching lines @@
   if (num_c < 0)
     num_c = 0;
 
   return SubString(s, start_i, start_i + num_c);
 }
 
 
 // ECMA-262 section 15.5.4.14
 function StringSplit(separator, limit) {
   var subject = ToString(this);
-  limit = (limit === void 0) ? 0xffffffff : ToUint32(limit);
+  limit = (IS_UNDEFINED(limit)) ? 0xffffffff : TO_UINT32(limit);
   if (limit === 0) return [];
 
   // ECMA-262 says that if separator is undefined, the result should
   // be an array of size 1 containing the entire string.  SpiderMonkey
   // and KJS have this behaviour only when no separator is given.  If
   // undefined is explicitly given, they convert it to a string and
   // use that.  We do as SpiderMonkey and KJS.
   if (%_ArgumentsLength() === 0) {
     return [subject];
   }
@@ skipping 78 matching lines @@
   if (separatorIndex === -1) return null;
 
   reusableMatchInfo[CAPTURE0] = separatorIndex;
   reusableMatchInfo[CAPTURE1] = separatorIndex + separator.length;
   return reusableMatchInfo;
 };
 
 
 // ECMA-262 section 15.5.4.15
 function StringSubstring(start, end) {
-  var s = ToString(this);
+  var s = this;
+  if (!IS_STRING(s)) s = ToString(s);
   var s_len = s.length;
+
   var start_i = TO_INTEGER(start);
+  if (start_i < 0) {
+    start_i = 0;
+  } else if (start_i > s_len) {
+    start_i = s_len;
+  }
+
   var end_i = s_len;
-  if (!IS_UNDEFINED(end))
+  if (!IS_UNDEFINED(end)) {
     end_i = TO_INTEGER(end);
-
-  if (start_i < 0) start_i = 0;
-  if (start_i > s_len) start_i = s_len;
-  if (end_i < 0) end_i = 0;
-  if (end_i > s_len) end_i = s_len;
-
-  if (start_i > end_i) {
-    var tmp = end_i;
-    end_i = start_i;
-    start_i = tmp;
+    if (end_i > s_len) {
+      end_i = s_len;
+    } else {
+      if (end_i < 0) end_i = 0;
+      if (start_i > end_i) {
+        var tmp = end_i;
+        end_i = start_i;
+        start_i = tmp;
+      }
+    }
   }
 
   return SubString(s, start_i, end_i);
 }
 
 
 // This is not a part of ECMA-262.
 function StringSubstr(start, n) {
   var s = ToString(this);
   var len;
@@ skipping 150 matching lines @@
 function StringSub() {
   return "<sub>" + this + "</sub>";
 }
 
 
 function StringSup() {
   return "<sup>" + this + "</sup>";
 }
 
 
-// StringBuilder support.
-
-function StringBuilder() {
-  this.elements = new $Array();
-}
-
-
+// ReplaceResultBuilder support.
 function ReplaceResultBuilder(str) {
   this.elements = new $Array();
   this.special_string = str;
 }
 
 
-ReplaceResultBuilder.prototype.add =
-StringBuilder.prototype.add = function(str) {
+ReplaceResultBuilder.prototype.add = function(str) {
   if (!IS_STRING(str)) str = ToString(str);
   if (str.length > 0) {
     var elements = this.elements;
     elements[elements.length] = str;
   }
 }
 
 
 ReplaceResultBuilder.prototype.addSpecialSlice = function(start, end) {
   var len = end - start;
   if (len == 0) return;
   var elements = this.elements;
   if (start < 0x80000 && len < 0x800) {
     elements[elements.length] = (start << 11) + len;
   } else {
     // 0 < len <= String::kMaxLength and Smi::kMaxValue >= String::kMaxLength,
     // so -len is a smi.
     elements[elements.length] = -len;
     elements[elements.length] = start;
   }
 }
 
 
-StringBuilder.prototype.generate = function() {
-  return %StringBuilderConcat(this.elements, "");
-}
-
-
 ReplaceResultBuilder.prototype.generate = function() {
-  return %StringBuilderConcat(this.elements, this.special_string);
+  var elements = this.elements;
+  return %StringBuilderConcat(elements, elements.length, this.special_string);
 }
 
 
 function StringToJSON(key) {
   return CheckJSONPrimitive(this.valueOf());
 }
 
 
 // -------------------------------------------------------------------
 
@@ skipping 44 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();