diff --git a/ChangeLog b/ChangeLog
index 81a1348614..67279cedbb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+1999-09-06  Andreas Schwab  <schwab@suse.de>
+
+	* time/tzset.c (compute_change): Replace slow loop to compute T by
+	simple algorithm.
+
 1999-09-06  Ulrich Drepper  <drepper@cygnus.com>
 
 	* iconvdata/iso-2022-jp.c: When translating to ISO-2022-JP* write
diff --git a/time/tzset.c b/time/tzset.c
index 24624fa188..6af2fbaf00 100644
--- a/time/tzset.c
+++ b/time/tzset.c
@@ -418,16 +418,23 @@ compute_change (rule, year)
      int year;
 {
   register time_t t;
-  int y;
 
   if (year != -1 && rule->computed_for == year)
-    /* Operations on times in 1969 will be slower.  Oh well.  */
+    /* Operations on times in 2 BC will be slower.  Oh well.  */
     return 1;
 
   /* First set T to January 1st, 0:00:00 GMT in YEAR.  */
-  t = 0;
-  for (y = 1970; y < year; ++y)
-    t += SECSPERDAY * (__isleap (y) ? 366 : 365);
+  if (year > 1970)
+    t = ((year - 1970) * 365
+	 + /* Compute the number of leapdays between 1970 and YEAR
+	      (exclusive).  There is a leapday every 4th year ...  */
+	 + ((year - 1) / 4 - 1970 / 4)
+	 /* ... except every 100th year ... */
+	 - ((year - 1) / 100 - 1970 / 100)
+	 /* ... but still every 400th year.  */
+	 + ((year - 1) / 400 - 1970 / 400)) * SECSPERDAY;
+  else
+    t = 0;
 
   switch (rule->type)
     {