Remove dependency on _mkgmtime to determine local timezone offset

src/platform-win32.cc

 // Copyright 2012 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 @@
 }
 
 
 int fopen_s(FILE** pFile, const char* filename, const char* mode) {
   *pFile = fopen(filename, mode);
   return *pFile != NULL ? 0 : 1;
 }
 
 
 #ifndef __MINGW64_VERSION_MAJOR
-
-// Not sure this the correct interpretation of _mkgmtime
-time_t _mkgmtime(tm* timeptr) {
-  return mktime(timeptr);
-}
-
-
 #define _TRUNCATE 0
 #define STRUNCATE 80
-
 #endif  // __MINGW64_VERSION_MAJOR
 
 
 int _vsnprintf_s(char* buffer, size_t sizeOfBuffer, size_t count,
                  const char* format, va_list argptr) {
   ASSERT(count == _TRUNCATE);
   return _vsnprintf(buffer, sizeOfBuffer, format, argptr);
 }
 
 
@@ skipping 420 matching lines @@
   double unchecked_posix_time = rounded_to_second.ToJSTime() / 1000;
   if (unchecked_posix_time > INT_MAX || unchecked_posix_time < 0) {
     return 0;
   }
   // Because _USE_32BIT_TIME_T is defined, time_t is a 32-bit int.
   time_t posix_time = static_cast<time_t>(unchecked_posix_time);
 
   // Convert to local time, as struct with fields for day, hour, year, etc.
   tm posix_local_time_struct;
   if (localtime_s(&posix_local_time_struct, &posix_time)) return 0;
-  // Convert local time in struct to POSIX time as if it were a UTC time.
-  time_t local_posix_time = _mkgmtime(&posix_local_time_struct);
-  Time localtime(1000.0 * local_posix_time);
 
-  return localtime.Diff(&rounded_to_second);
+  if (posix_local_time_struct.tm_isdst > 0)
+      return (tzinfo_.Bias + tzinfo_.DaylightBias) * -kMsPerMinute;
+  else if (posix_local_time_struct.tm_isdst == 0)
+      return (tzinfo_.Bias + tzinfo_.StandardBias) * -kMsPerMinute;
+  else
+      return tzinfo_.Bias * -kMsPerMinute;
 }
 
 
 // Return whether or not daylight savings time is in effect at this time.
 bool Time::InDST() {
   // Initialize timezone information, if needed.
   TzSet();
 
   // Determine if DST is in effect at the specified time.
   bool in_dst = false;
@@ skipping 1560 matching lines @@
 
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SamplerThread::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 
 } }  // namespace v8::internal