Move quoting of a JSON string to a specialized runtime function.

src/json.js

 // Copyright 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 48 matching lines @@
 
 function JSONParse(text, reviver) {
   var unfiltered = ParseJSONUnfiltered(text);
   if (IS_FUNCTION(reviver)) {
     return Revive({'': unfiltered}, '', reviver);
   } else {
     return unfiltered;
   }
 }
 
-var characterQuoteCache = {
-  '\b': '\\b',  // ASCII 8, Backspace
-  '\t': '\\t',  // ASCII 9, Tab
-  '\n': '\\n',  // ASCII 10, Newline
-  '\f': '\\f',  // ASCII 12, Formfeed
-  '\r': '\\r',  // ASCII 13, Carriage Return
-  '\"': '\\"',
-  '\\': '\\\\'
-};
-
-function QuoteSingleJSONCharacter(c) {
-  if (c in characterQuoteCache) {
-    return characterQuoteCache[c];
-  }
-  var charCode = c.charCodeAt(0);
-  var result;
-  if (charCode < 16) result = '\\u000';
-  else if (charCode < 256) result = '\\u00';
-  else if (charCode < 4096) result = '\\u0';
-  else result = '\\u';
-  result += charCode.toString(16);
-  characterQuoteCache[c] = result;
-  return result;
-}
-
 function QuoteJSONString(str) {
-  var quotable = /[\\\"\x00-\x1f]/g;
-  return '"' + str.replace(quotable, QuoteSingleJSONCharacter) + '"';
+  var quoted_str = %QuoteJSONString(str);
+  if (IS_STRING(quoted_str)) return quoted_str;
+  return '"' + str + '"';
 }
 
 function StackContains(stack, val) {
   var length = stack.length;
   for (var i = 0; i < length; i++) {
     if (stack[i] === val) {
       return true;
     }
   }
   return false;
@@ skipping 149 matching lines @@
 }
 
 function SetupJSON() {
   InstallFunctions($JSON, DONT_ENUM, $Array(
     "parse", JSONParse,
     "stringify", JSONStringify
   ));
 }
 
 SetupJSON();