Fix minor problems in Windows emulation of getloadavg.

 src/w32.c (getloadavg): Don't index samples[] array with negative
 indices.  Recover from wall-clock time being set backwards.

2 files changed, 23 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index aaa8788c2ba..0fe25e6fd63 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,8 @@
 2013-12-17  Eli Zaretskii  <eliz@gnu.org>
 
+        * w32.c (getloadavg): Don't index samples[] array with negative
+        indices.  Recover from wall-clock time being set backwards.
+
         * w32term.c (w32_initialize): Declare the argument of
         set_user_model as const.
 
diff --git a/src/w32.c b/src/w32.c
index e4678637cbb..159085e7f50 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -1732,9 +1732,28 @@ getloadavg (double loadavg[], int nelem)
   ULONGLONG idle, kernel, user;
   time_t now = time (NULL);
 
+  /* If system time jumped back for some reason, delete all samples
+     whose time is later than the current wall-clock time.  This
+     prevents load average figures from becoming frozen for prolonged
+     periods of time, when system time is reset backwards.  */
+  if (last_idx >= 0)
+    {
+      while (difftime (now, samples[last_idx].sample_time) < -1.0)
+        {
+          if (last_idx == first_idx)
+            {
+              first_idx = last_idx = -1;
+              break;
+            }
+          last_idx = buf_prev (last_idx);
+        }
+    }
+
   /* Store another sample.  We ignore samples that are less than 1 sec
      apart.  */
-  if (difftime (now, samples[last_idx].sample_time) >= 1.0 - 2*DBL_EPSILON*now)
+  if (last_idx < 0
+      || (difftime (now, samples[last_idx].sample_time)
+          >= 1.0 - 2*DBL_EPSILON*now))
     {
       sample_system_load (&idle, &kernel, &user);
       last_idx = buf_next (last_idx);