Subject: lisp_string_width and strings wider than INT_MAX
From: Paul Eggert <[email-masked]>
To: [email-masked]
Date: Sun, 15 May 2011 22:07:36 -0700
List-Id: <debbugs-submit.debbugs.gnu.org>

lisp_string_width requires that the precision be less than INT_MAX,
and if no precision is given, misbehaves badly when dealing with
strings whose widths are greater than INT_MAX.  To address this, I
plan to install the following patch (PATCH 3) after some more testing.
PATCH 3 depends on two obvious patches: PATCH 2 introduces a helper
no-return function string_overflow, and PATCH 1 updates to the latest
version of gnulib.

One thing about PATCH 3: when used in Emacs, the new lisp_string_width
correctly signals an overflow when the string's width cannot be
represented, but when used outside Emacs (in mulelib) it silently
ignores the problem, just as before.  I don't know much about mulelib
and so don't know how to address this.  But anyway, mulelib uses
should be no worse off than before.

PATCH 3 ---------------------------------------------------
=== modified file 'src/ChangeLog'
--- src/ChangeLog	2011-05-16 01:11:54 +0000
+++ src/ChangeLog	2011-05-16 01:25:38 +0000
@@ -1,5 +1,14 @@
 2011-05-16  Paul Eggert  <[email-masked]>
 
+	* character.c (lisp_string_width): Check for string overflow.
+	Use EMACS_INT, not int, for string indexes and lengths; in
+	particular, 2nd arg is now EMACS_INT, not int.  Do not crash if
+	the resulting string length overflows an EMACS_INT; instead,
+	report a string overflow if no precision given.  When checking for
+	precision exhaustion, use a check that cannot possibly have
+	integer overflow.
+	* character.h (lisp_string_width): Adjust to new signature.
+
 	* alloc.c (string_overflow): New function.
 	(Fmake_string): Use it.  This doesn't change behavior, but saves
 	a few bytes and will simplify future changes.

=== modified file 'src/character.c'
--- src/character.c	2011-05-16 01:11:54 +0000
+++ src/character.c	2011-05-16 01:17:19 +0000
@@ -35,6 +35,7 @@
 
 #include <sys/types.h>
 #include <setjmp.h>
+#include <intprops.h>
 #include "lisp.h"
 #include "character.h"
 #include "buffer.h"
@@ -404,7 +405,7 @@
    in *NCHARS and *NBYTES respectively.  */
 
 EMACS_INT
-lisp_string_width (Lisp_Object string, int precision,
+lisp_string_width (Lisp_Object string, EMACS_INT precision,
 		   EMACS_INT *nchars, EMACS_INT *nbytes)
 {
   EMACS_INT len = SCHARS (string);
@@ -419,7 +420,7 @@
 
   while (i < len)
     {
-      int chars, bytes, thiswidth;
+      EMACS_INT chars, bytes, thiswidth;
       Lisp_Object val;
       int cmp_id;
       EMACS_INT ignore, end;
@@ -437,7 +438,11 @@
 	  int c;
 
 	  if (multibyte)
-	    c = STRING_CHAR_AND_LENGTH (str + i_byte, bytes);
+	    {
+	      int cbytes;
+	      c = STRING_CHAR_AND_LENGTH (str + i_byte, cbytes);
+	      bytes = cbytes;
+	    }
 	  else
 	    c = str[i_byte], bytes = 1;
 	  chars = 1;
@@ -455,8 +460,14 @@
 	    }
 	}
 
-      if (precision > 0
-	  && (width + thiswidth > precision))
+      if (precision <= 0)
+	{
+#ifdef emacs
+	  if (INT_ADD_OVERFLOW (width, thiswidth))
+	    string_overflow ();
+#endif
+	}
+      else if (precision - width < thiswidth)
 	{
 	  *nchars = i;
 	  *nbytes = i_byte;

=== modified file 'src/character.h'
--- src/character.h	2011-04-11 03:39:45 +0000
+++ src/character.h	2011-05-16 01:13:28 +0000
@@ -612,7 +612,7 @@
 extern EMACS_INT strwidth (const char *, EMACS_INT);
 extern EMACS_INT c_string_width (const unsigned char *, EMACS_INT, int,
 				 EMACS_INT *, EMACS_INT *);
-extern EMACS_INT lisp_string_width (Lisp_Object, int,
+extern EMACS_INT lisp_string_width (Lisp_Object, EMACS_INT,
 				    EMACS_INT *, EMACS_INT *);
 
 extern Lisp_Object Qcharacterp;

PATCH 2 ---------------------------------------------------
=== modified file 'src/ChangeLog'
--- src/ChangeLog	2011-05-15 17:17:44 +0000
+++ src/ChangeLog	2011-05-16 01:11:54 +0000
@@ -1,3 +1,11 @@
+2011-05-16  Paul Eggert  <[email-masked]>
+
+	* alloc.c (string_overflow): New function.
+	(Fmake_string): Use it.  This doesn't change behavior, but saves
+	a few bytes and will simplify future changes.
+	* character.c (string_escape_byte8): Likewise.
+	* lisp.h (string_overflow): New decl.
+
 2011-05-15  Paul Eggert  <[email-masked]>
 
 	Fixups, following up to the user-interface timestamp change.

=== modified file 'src/alloc.c'
--- src/alloc.c	2011-05-12 07:07:06 +0000
+++ src/alloc.c	2011-05-16 01:11:54 +0000
@@ -2174,6 +2174,11 @@
   current_sblock = tb;
 }
 
+void
+string_overflow (void)
+{
+  error ("Maximum string size exceeded");
+}
 
 DEFUN ("make-string", Fmake_string, Smake_string, 2, 2, 0,
        doc: /* Return a newly created string of length LENGTH, with INIT in each element.
@@ -2206,7 +2211,7 @@
       EMACS_INT string_len = XINT (length);
 
       if (string_len > MOST_POSITIVE_FIXNUM / len)
-	error ("Maximum string size exceeded");
+	string_overflow ();
       nbytes = len * string_len;
       val = make_uninit_multibyte_string (string_len, nbytes);
       p = SDATA (val);

=== modified file 'src/character.c'
--- src/character.c	2011-05-12 07:07:06 +0000
+++ src/character.c	2011-05-16 01:11:54 +0000
@@ -823,7 +823,7 @@
     {
       if ((MOST_POSITIVE_FIXNUM - nchars) / 3 < byte8_count
 	  || (MOST_POSITIVE_FIXNUM - nbytes) / 2 < byte8_count)
-	error ("Maximum string size exceeded");
+	string_overflow ();
 
       /* Convert 2-byte sequence of byte8 chars to 4-byte octal.  */
       val = make_uninit_multibyte_string (nchars + byte8_count * 3,
@@ -832,7 +832,7 @@
   else
     {
       if ((MOST_POSITIVE_FIXNUM - nchars) / 3 < byte8_count)
-	error ("Maximum string size exceeded");
+	string_overflow ();
       /* Convert 1-byte sequence of byte8 chars to 4-byte octal.  */
       val = make_uninit_string (nbytes + byte8_count * 3);
     }

=== modified file 'src/lisp.h'
--- src/lisp.h	2011-05-15 17:17:44 +0000
+++ src/lisp.h	2011-05-16 01:11:54 +0000
@@ -2710,6 +2710,7 @@
 EXFUN (Fvector, MANY);
 EXFUN (Fmake_symbol, 1);
 EXFUN (Fmake_marker, 0);
+extern void string_overflow (void) NO_RETURN;
 EXFUN (Fmake_string, 2);
 extern Lisp_Object build_string (const char *);
 extern Lisp_Object make_string (const char *, EMACS_INT);

PATCH 1 ---------------------------------------------------
=== modified file 'doc/misc/texinfo.tex'
--- doc/misc/texinfo.tex	2011-04-06 05:07:27 +0000
+++ doc/misc/texinfo.tex	2011-05-16 00:51:54 +0000
@@ -3,7 +3,7 @@
 % Load plain if necessary, i.e., if running under initex.
 \expandafter\ifx\csname fmtname\endcsname\relax\input plain\fi
 %
-\def\texinfoversion{2011-03-25.11}
+\def\texinfoversion{2011-05-11.16}
 %
 % Copyright 1985, 1986, 1988, 1990, 1991, 1992, 1993, 1994, 1995,
 % 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
@@ -8424,7 +8424,7 @@
 %
 % Latin1 (ISO-8859-1) character definitions.
 \def\latonechardefs{%
-  \gdef^^a0{~}
+  \gdef^^a0{\tie}
   \gdef^^a1{\exclamdown}
   \gdef^^a2{\missingcharmsg{CENT SIGN}}
   \gdef^^a3{{\pounds}}
@@ -8546,7 +8546,7 @@
 
 % Latin2 (ISO-8859-2) character definitions.
 \def\lattwochardefs{%
-  \gdef^^a0{~}
+  \gdef^^a0{\tie}
   \gdef^^a1{\ogonek{A}}
   \gdef^^a2{\u{}}
   \gdef^^a3{\L}
@@ -9395,6 +9395,8 @@
 
 \message{and turning on texinfo input format.}
 
+\def^^L{\par} % remove \outer, so ^L can appear in an @comment
+
 % DEL is a comment character, in case @c does not suffice.
 \catcode`\^^? = 14

=== modified file 'lib/gnulib.mk'
--- lib/gnulib.mk	2011-05-04 07:19:21 +0000
+++ lib/gnulib.mk	2011-05-16 00:51:54 +0000
@@ -167,7 +167,8 @@
 
 ## begin gnulib module ignore-value
 
-libgnu_a_SOURCES += ignore-value.h
+
+EXTRA_DIST += ignore-value.h
 
 ## end   gnulib module ignore-value
 
@@ -779,6 +780,7 @@
 	      -e 's|@''GNULIB_GETLOGIN_R''@|$(GNULIB_GETLOGIN_R)|g' \
 	      -e 's|@''GNULIB_GETPAGESIZE''@|$(GNULIB_GETPAGESIZE)|g' \
 	      -e 's|@''GNULIB_GETUSERSHELL''@|$(GNULIB_GETUSERSHELL)|g' \
+	      -e 's|@''GNULIB_GROUP_MEMBER''@|$(GNULIB_GROUP_MEMBER)|g' \
 	      -e 's|@''GNULIB_LCHOWN''@|$(GNULIB_LCHOWN)|g' \
 	      -e 's|@''GNULIB_LINK''@|$(GNULIB_LINK)|g' \
 	      -e 's|@''GNULIB_LINKAT''@|$(GNULIB_LINKAT)|g' \
@@ -817,6 +819,7 @@
 	      -e 's|@''HAVE_GETHOSTNAME''@|$(HAVE_GETHOSTNAME)|g' \
 	      -e 's|@''HAVE_GETLOGIN''@|$(HAVE_GETLOGIN)|g' \
 	      -e 's|@''HAVE_GETPAGESIZE''@|$(HAVE_GETPAGESIZE)|g' \
+	      -e 's|@''HAVE_GROUP_MEMBER''@|$(HAVE_GROUP_MEMBER)|g' \
 	      -e 's|@''HAVE_LCHOWN''@|$(HAVE_LCHOWN)|g' \
 	      -e 's|@''HAVE_LINK''@|$(HAVE_LINK)|g' \
 	      -e 's|@''HAVE_LINKAT''@|$(HAVE_LINKAT)|g' \
@@ -883,9 +886,10 @@
 ## begin gnulib module verify
 
 if gl_GNULIB_ENABLED_verify
-libgnu_a_SOURCES += verify.h
 
 endif
+EXTRA_DIST += verify.h
+
 ## end   gnulib module verify
 
 ## begin gnulib module warn-on-use

=== modified file 'lib/intprops.h'
--- lib/intprops.h	2011-01-30 19:22:02 +0000
+++ lib/intprops.h	2011-05-16 00:51:54 +0000
@@ -17,70 +17,298 @@
 
 /* Written by Paul Eggert.  */
 
-#ifndef GL_INTPROPS_H
-# define GL_INTPROPS_H
-
-# include <limits.h>
+#ifndef _GL_INTPROPS_H
+#define _GL_INTPROPS_H
+
+#include <limits.h>
+
+/* Return a integer value, converted to the same type as the integer
+   expression E after integer type promotion.  V is the unconverted value.
+   E should not have side effects.  */
+#define _GL_INT_CONVERT(e, v) ((e) - (e) + (v))
 
 /* The extra casts in the following macros work around compiler bugs,
    e.g., in Cray C 5.0.3.0.  */
 
 /* True if the arithmetic type T is an integer type.  bool counts as
    an integer.  */
-# define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
+#define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
 
 /* True if negative values of the signed integer type T use two's
    complement, ones' complement, or signed magnitude representation,
    respectively.  Much GNU code assumes two's complement, but some
    people like to be portable to all possible C hosts.  */
-# define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
-# define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
-# define TYPE_SIGNED_MAGNITUDE(t) ((t) ~ (t) 0 < (t) -1)
+#define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
+#define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
+#define TYPE_SIGNED_MAGNITUDE(t) ((t) ~ (t) 0 < (t) -1)
+
+/* True if the signed integer expression E uses two's complement.  */
+#define _GL_INT_TWOS_COMPLEMENT(e) (~ _GL_INT_CONVERT (e, 0) == -1)
 
 /* True if the arithmetic type T is signed.  */
-# define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
-
-/* The maximum and minimum values for the integer type T.  These
+#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
+
+/* Return 1 if the integer expression E, after integer promotion, has
+   a signed type.  E should not have side effects.  */
+#define _GL_INT_SIGNED(e) (_GL_INT_CONVERT (e, -1) < 0)
+
+
+/* Minimum and maximum values for integer types and expressions.  These
    macros have undefined behavior if T is signed and has padding bits.
    If this is a problem for you, please let us know how to fix it for
    your host.  */
-# define TYPE_MINIMUM(t) \
-  ((t) (! TYPE_SIGNED (t) \
-        ? (t) 0 \
-        : TYPE_SIGNED_MAGNITUDE (t) \
-        ? ~ (t) 0 \
+
+/* The maximum and minimum values for the integer type T.  */
+#define TYPE_MINIMUM(t)                                                 \
+  ((t) (! TYPE_SIGNED (t)                                               \
+        ? (t) 0                                                         \
+        : TYPE_SIGNED_MAGNITUDE (t)                                     \
+        ? ~ (t) 0                                                       \
         : ~ TYPE_MAXIMUM (t)))
-# define TYPE_MAXIMUM(t) \
-  ((t) (! TYPE_SIGNED (t) \
-        ? (t) -1 \
+#define TYPE_MAXIMUM(t)                                                 \
+  ((t) (! TYPE_SIGNED (t)                                               \
+        ? (t) -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.
-   When compiling with GCC, INT_STRLEN_BOUND uses this macro to obtain a
-   tighter bound.  Otherwise, it overestimates the true bound by one byte
-   when applied to unsigned types of size 2, 4, 16, ... bytes.
-   The symbol signed_type_or_expr__ is private to this header file.  */
-# if __GNUC__ >= 2
-#  define signed_type_or_expr__(t) TYPE_SIGNED (__typeof__ (t))
-# else
-#  define signed_type_or_expr__(t) 1
-# endif
+/* The maximum and minimum values for the type of the expression E,
+   after integer promotion.  E should not have side effects.  */
+#define _GL_INT_MINIMUM(e)                                              \
+  (_GL_INT_SIGNED (e)                                                   \
+   ? - _GL_INT_TWOS_COMPLEMENT (e) - _GL_SIGNED_INT_MAXIMUM (e)         \
+   : _GL_INT_CONVERT (e, 0))
+#define _GL_INT_MAXIMUM(e)                                              \
+  (_GL_INT_SIGNED (e)                                                   \
+   ? _GL_SIGNED_INT_MAXIMUM (e)                                         \
+   : _GL_INT_CONVERT (e, -1))
+#define _GL_SIGNED_INT_MAXIMUM(e)                                       \
+  (((_GL_INT_CONVERT (e, 1) << (sizeof ((e) + 0) * CHAR_BIT - 2)) - 1) * 2 + 1)
+
+
+/* Return 1 if the __typeof__ keyword works.  This could be done by
+   'configure', but for now it's easier to do it by hand.  */
+#if 2 <= __GNUC__ || 0x5110 <= __SUNPRO_C
+# define _GL_HAVE___TYPEOF__ 1
+#else
+# define _GL_HAVE___TYPEOF__ 0
+#endif
+
+/* Return 1 if the integer type or expression T might be signed.  Return 0
+   if it is definitely unsigned.  This macro does not evaluate its argument,
+   and expands to an integer constant expression.  */
+#if _GL_HAVE___TYPEOF__
+# define _GL_SIGNED_TYPE_OR_EXPR(t) TYPE_SIGNED (__typeof__ (t))
+#else
+# define _GL_SIGNED_TYPE_OR_EXPR(t) 1
+#endif
 
 /* Bound on length of the string representing an unsigned integer
    value representable in B bits.  log10 (2.0) < 146/485.  The
    smallest value of B where this bound is not tight is 2621.  */
-# define INT_BITS_STRLEN_BOUND(b) (((b) * 146 + 484) / 485)
+#define INT_BITS_STRLEN_BOUND(b) (((b) * 146 + 484) / 485)
 
 /* Bound on length of the string representing an integer type or expression T.
    Subtract 1 for the sign bit if T is signed, and then add 1 more for
-   a minus sign if needed.  */
-# define INT_STRLEN_BOUND(t) \
-  (INT_BITS_STRLEN_BOUND (sizeof (t) * CHAR_BIT - signed_type_or_expr__ (t)) \
-   + signed_type_or_expr__ (t))
+   a minus sign if needed.
+
+   Because _GL_SIGNED_TYPE_OR_EXPR sometimes returns 0 when its argument is
+   signed, this macro may overestimate the true bound by one byte when
+   applied to unsigned types of size 2, 4, 16, ... bytes.  */
+#define INT_STRLEN_BOUND(t)                                     \
+  (INT_BITS_STRLEN_BOUND (sizeof (t) * CHAR_BIT                 \
+                          - _GL_SIGNED_TYPE_OR_EXPR (t))        \
+   + _GL_SIGNED_TYPE_OR_EXPR (t))
 
 /* Bound on buffer size needed to represent an integer type or expression T,
    including the terminating null.  */
-# define INT_BUFSIZE_BOUND(t) (INT_STRLEN_BOUND (t) + 1)
-
-#endif /* GL_INTPROPS_H */
+#define INT_BUFSIZE_BOUND(t) (INT_STRLEN_BOUND (t) + 1)
+
+
+/* Range overflow checks.
+
+   The INT_<op>_RANGE_OVERFLOW macros return 1 if the corresponding C
+   operators might not yield numerically correct answers due to
+   arithmetic overflow.  They do not rely on undefined or
+   implementation-defined behavior.  Their implementations are simple
+   and straightforward, but they are a bit harder to use than the
+   INT_<op>_OVERFLOW macros described below.
+
+   Example usage:
+
+     long int i = ...;
+     long int j = ...;
+     if (INT_MULTIPLY_RANGE_OVERFLOW (i, j, LONG_MIN, LONG_MAX))
+       printf ("multiply would overflow");
+     else
+       printf ("product is %ld", i * j);
+
+   Restrictions on *_RANGE_OVERFLOW macros:
+
+   These macros do not check for all possible numerical problems or
+   undefined or unspecified behavior: they do not check for division
+   by zero, for bad shift counts, or for shifting negative numbers.
+
+   These macros may evaluate their arguments zero or multiple times,
+   so the arguments should not have side effects.  The arithmetic
+   arguments (including the MIN and MAX arguments) must be of the same
+   integer type after the usual arithmetic conversions, and the type
+   must have minimum value MIN and maximum MAX.  Unsigned types should
+   use a zero MIN of the proper type.
+
+   These macros are tuned for constant MIN and MAX.  For commutative
+   operations such as A + B, they are also tuned for constant B.  */
+
+/* Return 1 if A + B would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  */
+#define INT_ADD_RANGE_OVERFLOW(a, b, min, max)          \
+  ((b) < 0                                              \
+   ? (a) < (min) - (b)                                  \
+   : (max) - (b) < (a))
+
+/* Return 1 if A - B would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  */
+#define INT_SUBTRACT_RANGE_OVERFLOW(a, b, min, max)     \
+  ((b) < 0                                              \
+   ? (max) + (b) < (a)                                  \
+   : (a) < (min) + (b))
+
+/* Return 1 if - A would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  */
+#define INT_NEGATE_RANGE_OVERFLOW(a, min, max)          \
+  ((min) < 0                                            \
+   ? (a) < - (max)                                      \
+   : 0 < (a))
+
+/* Return 1 if A * B would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  */
+#define INT_MULTIPLY_RANGE_OVERFLOW(a, b, min, max)     \
+  ((b) < 0                                              \
+   ? ((a) < 0                                           \
+      ? (a) < (max) / (b)                               \
+      : (b) < -1 && (min) / (b) < (a))                  \
+   : (0 < (b)                                           \
+      && ((a) < 0                                       \
+          ? (a) < (min) / (b)                           \
+          : (max) / (b) < (a))))
+
+/* Return 1 if A / B would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  Do not check for division by zero.  */
+#define INT_DIVIDE_RANGE_OVERFLOW(a, b, min, max)       \
+  ((min) < 0 && (b) == -1 && (a) < - (max))
+
+/* Return 1 if A % B would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  Do not check for division by zero.
+   Mathematically, % should never overflow, but on x86-like hosts
+   INT_MIN % -1 traps, and the C standard permits this, so treat this
+   as an overflow too.  */
+#define INT_REMAINDER_RANGE_OVERFLOW(a, b, min, max)    \
+  INT_DIVIDE_RANGE_OVERFLOW (a, b, min, max)
+
+/* Return 1 if A << B would overflow in [MIN,MAX] arithmetic.
+   See above for restrictions.  Here, MIN and MAX are for A only, and B need
+   not be of the same type as the other arguments.  The C standard says that
+   behavior is undefined for shifts unless 0 <= B < wordwidth, and that when
+   A is negative then A << B has undefined behavior and A >> B has
+   implementation-defined behavior, but do not check these other
+   restrictions.  */
+#define INT_LEFT_SHIFT_RANGE_OVERFLOW(a, b, min, max)   \
+  ((a) < 0                                              \
+   ? (a) < (min) >> (b)                                 \
+   : (max) >> (b) < (a))
+
+
+/* The _GL*_OVERFLOW macros have the same restrictions as the
+   *_RANGE_OVERFLOW macros, except that they do not assume that operands
+   (e.g., A and B) have the same type as MIN and MAX.  Instead, they assume
+   that the result (e.g., A + B) has that type.  */
+#define _GL_ADD_OVERFLOW(a, b, min, max)                                \
+  ((min) < 0 ? INT_ADD_RANGE_OVERFLOW (a, b, min, max)                  \
+   : (a) < 0 ? (b) <= (a) + (b)                                         \
+   : (b) < 0 ? (a) <= (a) + (b)                                         \
+   : (a) + (b) < (b))
+#define _GL_SUBTRACT_OVERFLOW(a, b, min, max)                           \
+  ((min) < 0 ? INT_SUBTRACT_RANGE_OVERFLOW (a, b, min, max)             \
+   : (a) < 0 ? 1                                                        \
+   : (b) < 0 ? (a) - (b) <= (a)                                         \
+   : (a) < (b))
+#define _GL_MULTIPLY_OVERFLOW(a, b, min, max)                           \
+  (((min) == 0 && (((a) < 0 && 0 < (b)) || ((b) < 0 && 0 < (a))))       \
+   || INT_MULTIPLY_RANGE_OVERFLOW (a, b, min, max))
+#define _GL_DIVIDE_OVERFLOW(a, b, min, max)                             \
+  ((min) < 0 ? (b) == _GL_INT_CONVERT (min, -1) && (a) < - (max)        \
+   : (a) < 0 ? (b) <= (a) + (b) - 1                                     \
+   : (b) < 0 && (a) + (b) <= (a))
+#define _GL_REMAINDER_OVERFLOW(a, b, min, max)                          \
+  ((min) < 0 ? (b) == _GL_INT_CONVERT (min, -1) && (a) < - (max)        \
+   : (a) < 0 ? (a) % (b) != ((max) - (b) + 1) % (b)                     \
+   : (b) < 0 && ! _GL_UNSIGNED_NEG_MULTIPLE (a, b, max))
+
+/* Return a nonzero value if A is a mathematical multiple of B, where
+   A is unsigned, B is negative, and MAX is the maximum value of A's
+   type.  A's type must be the same as (A % B)'s type.  Normally (A %
+   -B == 0) suffices, but things get tricky if -B would overflow.  */
+#define _GL_UNSIGNED_NEG_MULTIPLE(a, b, max)                            \
+  (((b) < -_GL_SIGNED_INT_MAXIMUM (b)                                   \
+    ? (_GL_SIGNED_INT_MAXIMUM (b) == (max)                              \
+       ? (a)                                                            \
+       : (a) % (_GL_INT_CONVERT (a, _GL_SIGNED_INT_MAXIMUM (b)) + 1))   \
+    : (a) % - (b))                                                      \
+   == 0)
+
+
+/* Integer overflow checks.
+
+   The INT_<op>_OVERFLOW macros return 1 if the corresponding C operators
+   might not yield numerically correct answers due to arithmetic overflow.
+   They work correctly on all known practical hosts, and do not rely
+   on undefined behavior due to signed arithmetic overflow.
+
+   Example usage:
+
+     long int i = ...;
+     long int j = ...;
+     if (INT_MULTIPLY_OVERFLOW (i, j))
+       printf ("multiply would overflow");
+     else
+       printf ("product is %ld", i * j);
+
+   These macros do not check for all possible numerical problems or
+   undefined or unspecified behavior: they do not check for division
+   by zero, for bad shift counts, or for shifting negative numbers.
+
+   These macros may evaluate their arguments zero or multiple times, so the
+   arguments should not have side effects.
+
+   These macros are tuned for their last argument being a constant.
+
+   Return 1 if the integer expressions A * B, A - B, -A, A * B, A / B,
+   A % B, and A << B would overflow, respectively.  */
+
+#define INT_ADD_OVERFLOW(a, b) \
+  _GL_BINARY_OP_OVERFLOW (a, b, _GL_ADD_OVERFLOW)
+#define INT_SUBTRACT_OVERFLOW(a, b) \
+  _GL_BINARY_OP_OVERFLOW (a, b, _GL_SUBTRACT_OVERFLOW)
+#define INT_NEGATE_OVERFLOW(a) \
+  INT_NEGATE_RANGE_OVERFLOW (a, _GL_INT_MINIMUM (a), _GL_INT_MAXIMUM (a))
+#define INT_MULTIPLY_OVERFLOW(a, b) \
+  _GL_BINARY_OP_OVERFLOW (a, b, _GL_MULTIPLY_OVERFLOW)
+#define INT_DIVIDE_OVERFLOW(a, b) \
+  _GL_BINARY_OP_OVERFLOW (a, b, _GL_DIVIDE_OVERFLOW)
+#define INT_REMAINDER_OVERFLOW(a, b) \
+  _GL_BINARY_OP_OVERFLOW (a, b, _GL_REMAINDER_OVERFLOW)
+#define INT_LEFT_SHIFT_OVERFLOW(a, b) \
+  INT_LEFT_SHIFT_RANGE_OVERFLOW (a, b, \
+                                 _GL_INT_MINIMUM (a), _GL_INT_MAXIMUM (a))
+
+/* Return 1 if the expression A <op> B would overflow,
+   where OP_RESULT_OVERFLOW (A, B, MIN, MAX) does the actual test,
+   assuming MIN and MAX are the minimum and maximum for the result type.
+
+   This macro assumes that A | B is a valid integer if both A and B are,
+   which is true of all known practical hosts.  If this is a problem
+   for you, please let us know how to fix it for your host.  */
+#define _GL_BINARY_OP_OVERFLOW(a, b, op_result_overflow)        \
+  op_result_overflow (a, b,                                     \
+                      _GL_INT_MINIMUM ((a) | (b)),              \
+                      _GL_INT_MAXIMUM ((a) | (b)))
+
+#endif /* _GL_INTPROPS_H */

=== modified file 'lib/unistd.in.h'
--- lib/unistd.in.h	2011-04-18 04:03:18 +0000
+++ lib/unistd.in.h	2011-05-16 00:51:54 +0000
@@ -871,6 +871,22 @@
 #endif

+#if @GNULIB_GROUP_MEMBER@
+/* Determine whether group id is in calling user's group list.  */
+# if !@HAVE_GROUP_MEMBER@
+_GL_FUNCDECL_SYS (group_member, int, (gid_t gid));
+# endif
+_GL_CXXALIAS_SYS (group_member, int, (gid_t gid));
+_GL_CXXALIASWARN (group_member);
+#elif defined GNULIB_POSIXCHECK
+# undef group_member
+# if HAVE_RAW_DECL_GROUP_MEMBER
+_GL_WARN_ON_USE (group_member, "group_member is unportable - "
+                 "use gnulib module group-member for portability");
+# endif
+#endif
+
+
 #if @GNULIB_LCHOWN@
 /* Change the owner of FILE to UID (if UID is not -1) and the group of FILE
    to GID (if GID is not -1).  Do not follow symbolic links.

=== modified file 'm4/unistd_h.m4'
--- m4/unistd_h.m4	2011-04-18 04:03:18 +0000
+++ m4/unistd_h.m4	2011-05-16 00:51:54 +0000
@@ -1,4 +1,4 @@
-# unistd_h.m4 serial 55
+# unistd_h.m4 serial 56
 dnl Copyright (C) 2006-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -36,8 +36,8 @@
     ]], [chown dup2 dup3 environ euidaccess faccessat fchdir fchownat
     fsync ftruncate getcwd getdomainname getdtablesize getgroups
     gethostname getlogin getlogin_r getpagesize getusershell setusershell
-    endusershell lchown link linkat lseek pipe pipe2 pread pwrite readlink
-    readlinkat rmdir sleep symlink symlinkat ttyname_r unlink unlinkat
+    endusershell group_member lchown link linkat lseek pipe pipe2 pread pwrite
+    readlink readlinkat rmdir sleep symlink symlinkat ttyname_r unlink unlinkat
     usleep])
 ])
 
@@ -72,6 +72,7 @@
   GNULIB_GETLOGIN_R=0;           AC_SUBST([GNULIB_GETLOGIN_R])
   GNULIB_GETPAGESIZE=0;          AC_SUBST([GNULIB_GETPAGESIZE])
   GNULIB_GETUSERSHELL=0;         AC_SUBST([GNULIB_GETUSERSHELL])
+  GNULIB_GROUP_MEMBER=0;         AC_SUBST([GNULIB_GROUP_MEMBER])
   GNULIB_LCHOWN=0;               AC_SUBST([GNULIB_LCHOWN])
   GNULIB_LINK=0;                 AC_SUBST([GNULIB_LINK])
   GNULIB_LINKAT=0;               AC_SUBST([GNULIB_LINKAT])
@@ -110,6 +111,7 @@
   HAVE_GETHOSTNAME=1;     AC_SUBST([HAVE_GETHOSTNAME])
   HAVE_GETLOGIN=1;        AC_SUBST([HAVE_GETLOGIN])
   HAVE_GETPAGESIZE=1;     AC_SUBST([HAVE_GETPAGESIZE])
+  HAVE_GROUP_MEMBER=1;    AC_SUBST([HAVE_GROUP_MEMBER])
   HAVE_LCHOWN=1;          AC_SUBST([HAVE_LCHOWN])
   HAVE_LINK=1;            AC_SUBST([HAVE_LINK])
   HAVE_LINKAT=1;          AC_SUBST([HAVE_LINKAT])