Simplify JSON stringify and add special case for default replacer and space.

src/runtime.cc

 // 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 4601 matching lines @@
   int length = characters.length();
   int quoted_length = 0;
   for (int i = 0; i < length; i++) {
     unsigned int c = characters[i];
     if (sizeof(Char) > 1u) {
       quoted_length += (c >= kQuoteTableLength) ? 1 : JsonQuoteLengths[c];
     } else {
       quoted_length += JsonQuoteLengths[c];
     }
   }
-  if (quoted_length == length) {
-    return Heap::undefined_value();
-  }
   Counters::quote_json_char_count.Increment(length);
 
   // Add space for quotes.
   quoted_length += 2;
 
   MaybeObject* new_alloc = AllocateRawString<StringType>(quoted_length);
   Object* new_object;
   if (!new_alloc->ToObject(&new_object)) {
     Counters::quote_json_char_recount.Increment(length);
     return new_alloc;
   }
   StringType* new_string = StringType::cast(new_object);
 
 
   STATIC_ASSERT(SeqTwoByteString::kHeaderSize == SeqAsciiString::kHeaderSize);
   Char* write_cursor = reinterpret_cast<Char*>(
       new_string->address() + SeqAsciiString::kHeaderSize);
   *(write_cursor++) = '"';
   const Char* read_cursor = characters.start();
-  const Char* end = read_cursor + length;
-  while (read_cursor < end) {
-    Char c = *(read_cursor++);
-    if (sizeof(Char) > 1u && static_cast<unsigned>(c) >= kQuoteTableLength) {
-      *(write_cursor++) = c;
-    } else {
-      const char* replacement = JsonQuotes[static_cast<unsigned>(c)];
-      if (!replacement) {
+  if (quoted_length == length + 2) {
+    CopyChars(write_cursor, read_cursor, length);
+    write_cursor += length;
+  } else {
+    const Char* end = read_cursor + length;
+    while (read_cursor < end) {
+      Char c = *(read_cursor++);
+      if (sizeof(Char) > 1u && static_cast<unsigned>(c) >= kQuoteTableLength) {
         *(write_cursor++) = c;
       } else {
-        write_cursor = WriteString(write_cursor, replacement);
+        const char* replacement = JsonQuotes[static_cast<unsigned>(c)];
+        if (!replacement) {
+          *(write_cursor++) = c;
+        } else {
+          write_cursor = WriteString(write_cursor, replacement);
+        }
       }
     }
   }
   *(write_cursor++) = '"';
   ASSERT_EQ(SeqAsciiString::kHeaderSize + quoted_length * sizeof(Char),
             reinterpret_cast<Address>(write_cursor) - new_string->address());
   return new_string;
 }
 
 
@@ skipping 10 matching lines @@
     ASSERT(str->IsFlat());
   }
   if (str->IsTwoByteRepresentation()) {
     return QuoteJsonString<uc16, SeqTwoByteString>(str->ToUC16Vector());
   } else {
     return QuoteJsonString<char, SeqAsciiString>(str->ToAsciiVector());
   }
 }
 
 
+
 static MaybeObject* Runtime_StringParseInt(Arguments args) {
   NoHandleAllocation ha;
 
   CONVERT_CHECKED(String, s, args[0]);
   CONVERT_SMI_CHECKED(radix, args[1]);
 
   s->TryFlatten();
 
   RUNTIME_ASSERT(radix == 0 || (2 <= radix && radix <= 36));
   double value = StringToInt(s, radix);
@@ skipping 5788 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal