Correct GMT offsets for New Zealand and the Kingdom of Tonga, bug 591845. r=brendan, CLOSED TREE

js/src/prmjtime.cpp

@@ -98,6 +98,21 @@ extern int gettimeofday(struct timeval *tv);
 #define PRMJ_YEAR_SECONDS (PRMJ_DAY_SECONDS * PRMJ_YEAR_DAYS)
 #define PRMJ_MAX_UNIX_TIMET 2145859200L /*time_t value equiv. to 12/31/2037 */
 
+/* Get the local time. localtime_r is preferred as it is reentrant. */
+static inline bool
+ComputeLocalTime(time_t local, struct tm *ptm)
+{
+#ifdef HAVE_LOCALTIME_R
+    return localtime_r(&local, ptm);
+#else
+    struct tm *otm = localtime(&local);
+    if (!otm)
+        return false;
+    *ptm = *otm;
+    return true;
+#endif
+}
+
 /*
  * get the difference in seconds between this time zone and UTC (GMT)
  */
@@ -115,26 +130,25 @@ PRMJ_LocalGMTDifference()
 
     /*
      * Get the difference between this time zone and GMT, by checking the local
-     * time at the epoch.
+     * time for days 0 and 180 of 1970, using a date for which daylight savings
+     * time was not in effect.
      */
-    time_t local = 0;
+    int day = 0;
     struct tm tm;
-#ifndef HAVE_LOCALTIME_R
-    struct tm *ptm = localtime(&local);
-    if (!ptm)
+
+    if (!ComputeLocalTime(0, &tm))
         return 0;
-    tm = *ptm;
-#else
-    localtime_r(&local, &tm);
-#endif
+    if (tm.tm_isdst > 0) {
+        day = 180;
+        if (!ComputeLocalTime(PRMJ_DAY_SECONDS * day, &tm))
+            return 0;
+    }
 
-    JSInt32 time = (tm.tm_hour * 3600)
-                 + (tm.tm_min * 60)
-                 + tm.tm_sec;
-    time = (24 * 3600) - time;
+    int time = (tm.tm_hour * 3600) + (tm.tm_min * 60) + tm.tm_sec;
+    time = PRMJ_DAY_SECONDS - time;
 
-    if (time >= (12 * 3600))
-        time -= (24 * 3600);
+    if (tm.tm_yday == day)
+        time -= PRMJ_DAY_SECONDS;
 
     return time;
 }
@@ -684,16 +698,9 @@ DSTOffsetCache::computeDSTOffsetMilliseconds(int64 localTimeSeconds)
     _tzset();
 #endif
 
-    time_t local = static_cast<time_t>(localTimeSeconds);
     struct tm tm;
-#ifndef HAVE_LOCALTIME_R
-    struct tm *ptm = localtime(&local);
-    if (!ptm)
+    if (!ComputeLocalTime(static_cast<time_t>(localTimeSeconds), &tm))
         return 0;
-    tm = *ptm;
-#else
-    localtime_r(&local, &tm); /* get dst information */
-#endif
 
     JSInt32 base = PRMJ_LocalGMTDifference();