One element cache for localtime.

src/date.js

 // Copyright 2006-2008 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 220 matching lines @@
   return Modulo(DAY(time) + 4, 7);
 }
 
 
 function LocalTime(time) {
   if (NUMBER_IS_NAN(time)) return time;
   // DaylightSavingsOffset called before local_time_offset used.
   return time + DaylightSavingsOffset(time) + local_time_offset;
 }
 
+
+var ltcache = {
+  key: null, 
+  val: null
+};
+
 function LocalTimeNoCheck(time) {
+  var ltc = ltcache;
+  if (%_ObjectEquals(time, ltc.key)) return ltc.val;
   if (time < -MAX_TIME_MS || time > MAX_TIME_MS) {
     return $NaN;
   }
 
   // Inline the DST offset cache checks for speed.
   // The cache is hit, or DaylightSavingsOffset is called,
   // before local_time_offset is used.
   var cache = DST_offset_cache;
   if (cache.start <= time && time <= cache.end) {
     var dst_offset = cache.offset;
   } else {
     var dst_offset = DaylightSavingsOffset(time);
   }
-  return time + local_time_offset + dst_offset;
+  ltc.key = time;
+  return (ltc.val = time + local_time_offset + dst_offset);
 }
 
 
 function UTC(time) {
   if (NUMBER_IS_NAN(time)) return time;
   // local_time_offset is needed before the call to DaylightSavingsOffset,
   // so it may be uninitialized.
   if (IS_UNDEFINED(local_time_offset)) {
     local_time_offset = %DateLocalTimeOffset();
   }
@@ skipping 853 matching lines @@
     "toGMTString", DateToGMTString,
     "toUTCString", DateToUTCString,
     "getYear", DateGetYear,
     "setYear", DateSetYear,
     "toISOString", DateToISOString,
     "toJSON", DateToJSON
   ));
 }
 
 SetupDate();