API: Correct documentation of String::WriteUtf8, String::Write...

src/api.cc

 // Copyright 2010 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 3109 matching lines @@
   LOG_API("String::Write");
   ENTER_V8;
   ASSERT(start >= 0 && length >= -1);
   i::Handle<i::String> str = Utils::OpenHandle(this);
   StringTracker::RecordWrite(str);
   if (hints & HINT_MANY_WRITES_EXPECTED) {
     // Flatten the string for efficiency.  This applies whether we are
     // using StringInputBuffer or Get(i) to access the characters.
     str->TryFlatten();
   }
-  int end = length;
-  if ( (length == -1) || (length > str->length() - start) )
-    end = str->length() - start;
+  int end = start + length;
+  if ((length == -1) || (length > str->length() - start) )
+    end = str->length();
   if (end < 0) return 0;
   i::String::WriteToFlat(*str, buffer, start, end);
-  if (length == -1 || end < length)
-    buffer[end] = '\0';
-  return end;
+  if (length == -1 || end - start < length) {
+    buffer[end - start] = '\0';
+  }
+  return end - start;
 }
 
 
 bool v8::String::IsExternal() const {
   EnsureInitialized("v8::String::IsExternal()");
   i::Handle<i::String> str = Utils::OpenHandle(this);
   return i::StringShape(*str).IsExternalTwoByte();
 }
 
 
@@ skipping 1957 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* thread_local =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   thread_local->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal