* m4/mktime.m4 (AC_FUNC_MKTIME): Sync from Autoconf.

Include <limits.h>, and use its INT_MAX to rewrite the
j loop so that it does not overflow 'int'.  Problem reported by
Ralf Wildenhues in
<http://lists.gnu.org/archive/html/bug-gnulib/2006-12/msg00084.html>.
Play it safe by shifting left by 1 rather than multiplying by 2,
as GCC is less likely to optimize this away when the value
is signed (when it assumes overflow leads to undefined behavior).
Also, don't assume time_t uses two's complement.

1 files changed, 17 insertions, 11 deletions

diff --git a/m4/mktime.m4 b/m4/mktime.m4
index ffc05e4417..a65a369b19 100644
--- a/m4/mktime.m4
+++ b/m4/mktime.m4
@@ -1,4 +1,4 @@
-#serial 8
+#serial 9
 dnl Copyright (C) 2002, 2003, 2005, 2006 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,10 +6,10 @@ dnl with or without modifications, as long as this notice is preserved.
 
 dnl From Jim Meyering.
 
-# Redefine AC_FUNC_MKTIME, to fix a bug in Autoconf 2.60a and earlier.
+# Redefine AC_FUNC_MKTIME, to fix a bug in Autoconf 2.61a and earlier.
 # This redefinition can be removed once a new version of Autoconf is assumed.
 # The redefinition is taken from
-# <http://cvs.sv.gnu.org/viewcvs/*checkout*/autoconf/lib/autoconf/functions.m4?rev=1.108&root=autoconf>.
+# <http://cvs.sv.gnu.org/viewcvs/*checkout*/autoconf/autoconf/lib/autoconf/functions.m4?rev=1.119>.
 # AC_FUNC_MKTIME
 # --------------
 AC_DEFUN([AC_FUNC_MKTIME],
@@ -30,6 +30,7 @@ AC_CACHE_CHECK([for working mktime], ac_cv_func_working_mktime,
 # endif
 #endif
 
+#include <limits.h>
 #include <stdlib.h>
 
 #ifdef HAVE_UNISTD_H
@@ -178,12 +179,15 @@ main ()
      isn't worth using anyway.  */
   alarm (60);
 
-  for (time_t_max = 1; 0 < time_t_max; time_t_max *= 2)
-    continue;
-  time_t_max--;
-  if ((time_t) -1 < 0)
-    for (time_t_min = -1; (time_t) (time_t_min * 2) < 0; time_t_min *= 2)
-      continue;
+  for (;;)
+    {
+      t = (time_t_max << 1) + 1;
+      if (t <= time_t_max)
+	break;
+      time_t_max = t;
+    }
+  time_t_min = - ((time_t) ~ (time_t) 0 == (time_t) -1) - time_t_max;
+
   delta = time_t_max / 997; /* a suitable prime number */
   for (i = 0; i < N_STRINGS; i++)
     {
@@ -198,10 +202,12 @@ main ()
 	     && mktime_test ((time_t) (60 * 60 * 24))))
 	return 1;
 
-      for (j = 1; 0 < j; j *= 2)
+      for (j = 1; ; j <<= 1)
 	if (! bigtime_test (j))
 	  return 1;
-      if (! bigtime_test (j - 1))
+	else if (INT_MAX / 2 < j)
+	  break;
+      if (! bigtime_test (INT_MAX))
 	return 1;
     }
   return ! (irix_6_4_bug () && spring_forward_gap () && year_2050_test ());