From: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri, 22 Dec 2006 08:42:17 +0000 (+0000)
Subject: * lib/autoconf/functions.m4 (AC_FUNC_MKTIME):
X-Git-Tag: v2.62~380
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7bd79987b05c64647c168df92c6151adbfb1b283;p=thirdparty%2Fautoconf.git

* lib/autoconf/functions.m4 (AC_FUNC_MKTIME):
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.
---

diff --git a/ChangeLog b/ChangeLog
index 50086131..94cfae32 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2006-12-22  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* lib/autoconf/functions.m4 (AC_FUNC_MKTIME):
+	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.
+
 2006-12-20  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
 
 	* tests/torture.at (Substitute a 2000-byte string): Avoid using
diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index 185376e9..a34c9f0e 100644
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -984,6 +984,7 @@ AC_CACHE_CHECK([for working mktime], ac_cv_func_working_mktime,
 # endif
 #endif
 
+#include <limits.h>
 #include <stdlib.h>
 
 #ifdef HAVE_UNISTD_H
@@ -1132,12 +1133,15 @@ 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++)
     {
@@ -1152,10 +1156,12 @@ 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 ());