TYPE_MAXIMUM: avoid theoretically undefined behavior

* lib/intprops.h (TYPE_MINIMUM, TYPE_MAXIMUM): Do not shift a
negative number, which the C Standard says has undefined behavior.
In practice this is not a problem, but might as well do it by the book.
Reported by Rich Felker and Eric Blake; see
<http://lists.gnu.org/archive/html/bug-gnulib/2011-01/msg00493.html>.
* lib/strtol.c (TYPE_MINIMUM, TYPE_MAXIMUM): Likewise.
* m4/mktime.m4 (AC_FUNC_MKTIME): Likewise.
* m4/nanosleep.m4 (gl_FUNC_NANOSLEEP): Likewise.
* m4/parse-datetime.m4 (gl_PARSE_DATETIME): Likewise.
* m4/stdint.m4 (gl_STDINT_H): Likewise.
* lib/mktime.c (TYPE_MAXIMUM): Redo slightly to match the others.

diff --git a/ChangeLog b/ChangeLog
index f6454e83418a7aa1ce0652858576e22059235a3c..da526748a56e97391ac4e911bd0412ddc422b6c6 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,18 @@
 2011-01-29  Paul Eggert  <eggert@cs.ucla.edu>
 
+       TYPE_MAXIMUM: avoid theoretically undefined behavior
+       * lib/intprops.h (TYPE_MINIMUM, TYPE_MAXIMUM): Do not shift a
+       negative number, which the C Standard says has undefined behavior.
+       In practice this is not a problem, but might as well do it by the book.
+       Reported by Rich Felker and Eric Blake; see
+       <http://lists.gnu.org/archive/html/bug-gnulib/2011-01/msg00493.html>.
+       * lib/strtol.c (TYPE_MINIMUM, TYPE_MAXIMUM): Likewise.
+       * m4/mktime.m4 (AC_FUNC_MKTIME): Likewise.
+       * m4/nanosleep.m4 (gl_FUNC_NANOSLEEP): Likewise.
+       * m4/parse-datetime.m4 (gl_PARSE_DATETIME): Likewise.
+       * m4/stdint.m4 (gl_STDINT_H): Likewise.
+       * lib/mktime.c (TYPE_MAXIMUM): Redo slightly to match the others.
+
        mktime: #undef mktime before #defining it
        * lib/mktime.c (mktime) [DEBUG]: #undef mktime before #defining it.
 

diff --git a/lib/intprops.h b/lib/intprops.h
index 511a5aa98907c5dd94edfb1b7936bbe02190f105..58b1b3fbf449ea6e36edc1b4301d54d3103d9030 100644 (file)
--- a/lib/intprops.h
+++ b/lib/intprops.h
@@ -49,11 +49,11 @@
         ? (t) 0 \
         : TYPE_SIGNED_MAGNITUDE (t) \
         ? ~ (t) 0 \
-        : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
+        : ~ TYPE_MAXIMUM (t)))
 # define TYPE_MAXIMUM(t) \
   ((t) (! TYPE_SIGNED (t) \
         ? (t) -1 \
-        : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+        : ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 
 /* Return zero if T can be determined to be an unsigned type.
    Otherwise, return 1.

diff --git a/lib/mktime.c b/lib/mktime.c
index d35bdd0441b85e8a24e82cd0928623a0a9fba662..2486514065aa22a93239063f0a388746b6cb587b 100644 (file)
--- a/lib/mktime.c
+++ b/lib/mktime.c
@@ -113,7 +113,7 @@ typedef long long int long_int;
 #define TYPE_MAXIMUM(t) \
   ((t) (! TYPE_SIGNED (t) \
         ? (t) -1 \
-        : (((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) << 1) + 1)))
+        : ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 
 #ifndef TIME_T_MIN
 # define TIME_T_MIN TYPE_MINIMUM (time_t)

diff --git a/lib/strtol.c b/lib/strtol.c
index 747d70ed3ff4db3b6a13f0255266b5324a61f307..b6a761ecb9c0299ec1ab208c9cdd6e59203b6469 100644 (file)
--- a/lib/strtol.c
+++ b/lib/strtol.c
@@ -141,11 +141,11 @@
          ? (t) 0 \
          : TYPE_SIGNED_MAGNITUDE (t) \
          ? ~ (t) 0 \
-         : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
+         : ~ TYPE_MAXIMUM (t)))
 # define TYPE_MAXIMUM(t) \
    ((t) (! TYPE_SIGNED (t) \
          ? (t) -1 \
-         : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+         : ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 
 # ifndef ULLONG_MAX
 #  define ULLONG_MAX TYPE_MAXIMUM (unsigned long long)

diff --git a/m4/mktime.m4 b/m4/mktime.m4
index 7836b76acb15809c8da863de37a491d4f9f3ee35..56b2416d619302fba98577929692500717d61f3c 100644 (file)
--- a/m4/mktime.m4
+++ b/m4/mktime.m4
@@ -1,4 +1,4 @@
-# serial 18
+# serial 19
 dnl Copyright (C) 2002-2003, 2005-2007, 2009-2011 Free Software Foundation,
 dnl Inc.
 dnl This file is free software; the Free Software Foundation
@@ -175,12 +175,13 @@ main ()
 
   time_t_max = (! time_t_signed
                 ? (time_t) -1
-                : ~ (~ (time_t) 0 << (sizeof (time_t) * CHAR_BIT - 1)));
+                : ((((time_t) 1 << (sizeof (time_t) * CHAR_BIT - 2)) - 1)
+                   * 2 + 1));
   time_t_min = (! time_t_signed
                 ? (time_t) 0
                 : time_t_signed_magnitude
                 ? ~ (time_t) 0
-                : ~ (time_t) 0 << (sizeof (time_t) * CHAR_BIT - 1));
+                : ~ time_t_max);
 
   delta = time_t_max / 997; /* a suitable prime number */
   for (i = 0; i < N_STRINGS; i++)

diff --git a/m4/nanosleep.m4 b/m4/nanosleep.m4
index 233f1c19042f756fd540cf665dbc4dd712b922dd..34493bb3a632d8cf031a1eec04c7069d717a4763 100644 (file)
--- a/m4/nanosleep.m4
+++ b/m4/nanosleep.m4
@@ -1,4 +1,4 @@
-# serial 32
+# serial 33
 
 dnl From Jim Meyering.
 dnl Check for the nanosleep function.
@@ -58,7 +58,7 @@ AC_DEFUN([gl_FUNC_NANOSLEEP],
           #define TYPE_MAXIMUM(t) \
             ((t) (! TYPE_SIGNED (t) \
                   ? (t) -1 \
-                  : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+                  : ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 
           static void
           check_for_SIGALRM (int sig)

diff --git a/m4/parse-datetime.m4 b/m4/parse-datetime.m4
index 2341de95051f15c0bb2465e82b457cb4bd81f9f3..e665ef37042c66a2cda7478a6b6b80b0e0038fd6 100644 (file)
--- a/m4/parse-datetime.m4
+++ b/m4/parse-datetime.m4
@@ -1,4 +1,4 @@
-# parse-datetime.m4 serial 18
+# parse-datetime.m4 serial 19
 dnl Copyright (C) 2002-2006, 2008-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -41,9 +41,11 @@ AC_DEFUN([gl_PARSE_DATETIME],
 #include <time.h> /* for time_t */
 #include <limits.h> /* for CHAR_BIT, LONG_MIN, LONG_MAX */
 #define TYPE_MINIMUM(t) \
-  ((t) ((t) 0 < (t) -1 ? (t) 0 : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
+  ((t) ((t) 0 < (t) -1 ? (t) 0 : ~ TYPE_MAXIMUM (t)))
 #define TYPE_MAXIMUM(t) \
-  ((t) ((t) 0 < (t) -1 ? (t) -1 : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+  ((t) ((t) 0 < (t) -1 \
+        ? (t) -1 \
+        : ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 typedef int verify_min[2 * (LONG_MIN <= TYPE_MINIMUM (time_t)) - 1];
 typedef int verify_max[2 * (TYPE_MAXIMUM (time_t) <= LONG_MAX) - 1];
        ]])],

diff --git a/m4/stdint.m4 b/m4/stdint.m4
index 43e1f702122722b898739d91e488825b16ed1044..26654c68e09d49637c384066875caad156b83cb6 100644 (file)
--- a/m4/stdint.m4
+++ b/m4/stdint.m4
@@ -1,4 +1,4 @@
-# stdint.m4 serial 36
+# stdint.m4 serial 37
 dnl Copyright (C) 2001-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -145,9 +145,11 @@ uintmax_t j = UINTMAX_MAX;
 
 #include <limits.h> /* for CHAR_BIT */
 #define TYPE_MINIMUM(t) \
-  ((t) ((t) 0 < (t) -1 ? (t) 0 : ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
+  ((t) ((t) 0 < (t) -1 ? (t) 0 : ~ TYPE_MAXIMUM (t)))
 #define TYPE_MAXIMUM(t) \
-  ((t) ((t) 0 < (t) -1 ? (t) -1 : ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+  ((t) ((t) 0 < (t) -1 \
+        ? (t) -1 \
+        : ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 struct s {
   int check_PTRDIFF:
       PTRDIFF_MIN == TYPE_MINIMUM (ptrdiff_t)