X-Git-Url: https://code.delx.au/gnu-emacs/blobdiff_plain/e61d39cddfd015032a6419ce75c36ecdf1e9fe9f..dc294483af221066724f1007a595016b47fb5814:/lib/timespec-sub.c

diff --git a/lib/timespec-sub.c b/lib/timespec-sub.c
index 7c4c781b7f..63cc142c1b 100644
--- a/lib/timespec-sub.c
+++ b/lib/timespec-sub.c
@@ -1,6 +1,6 @@
 /* Subtract two struct timespec values.
 
-   Copyright (C) 2011-2012 Free Software Foundation, Inc.
+   Copyright (C) 2011-2016 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -18,8 +18,8 @@
 /* Written by Paul Eggert.  */
 
 /* Return the difference between two timespec values A and B.  On
-   overflow, return an extremal value.  This assumes 0 <= tv_nsec <=
-   999999999.  */
+   overflow, return an extremal value.  This assumes 0 <= tv_nsec <
+   TIMESPEC_RESOLUTION.  */
 
 #include <config.h>
 #include "timespec.h"
@@ -29,43 +29,43 @@
 struct timespec
 timespec_sub (struct timespec a, struct timespec b)
 {
-  struct timespec r;
   time_t rs = a.tv_sec;
   time_t bs = b.tv_sec;
   int ns = a.tv_nsec - b.tv_nsec;
   int rns = ns;
+  time_t tmin = TYPE_MINIMUM (time_t);
+  time_t tmax = TYPE_MAXIMUM (time_t);
 
   if (ns < 0)
     {
-      rns = ns + 1000000000;
-      if (rs == TYPE_MINIMUM (time_t))
-        {
-          if (bs <= 0)
-            goto low_overflow;
-          bs--;
-        }
-      else
+      rns = ns + TIMESPEC_RESOLUTION;
+      if (bs < tmax)
+        bs++;
+      else if (- TYPE_SIGNED (time_t) < rs)
         rs--;
+      else
+        goto low_overflow;
     }
 
-  if (INT_SUBTRACT_OVERFLOW (rs, bs))
+  /* INT_SUBTRACT_WRAPV is not appropriate since time_t might be unsigned.
+     In theory time_t might be narrower than int, so plain
+     INT_SUBTRACT_OVERFLOW does not suffice.  */
+  if (! INT_SUBTRACT_OVERFLOW (rs, bs) && tmin <= rs - bs && rs - bs <= tmax)
+    rs -= bs;
+  else
     {
       if (rs < 0)
         {
         low_overflow:
-          rs = TYPE_MINIMUM (time_t);
+          rs = tmin;
           rns = 0;
         }
       else
         {
-          rs = TYPE_MAXIMUM (time_t);
-          rns = 999999999;
+          rs = tmax;
+          rns = TIMESPEC_RESOLUTION - 1;
         }
     }
-  else
-    rs -= bs;
 
-  r.tv_sec = rs;
-  r.tv_nsec = rns;
-  return r;
+  return make_timespec (rs, rns);
 }