Update gnulib files.

10 files changed, 554 insertions, 0 deletions

diff --git a/gl/Makefile.am b/gl/Makefile.am
index c6c10ea680..0ec3251f58 100644
--- a/gl/Makefile.am
+++ b/gl/Makefile.am
@@ -358,6 +358,15 @@ EXTRA_DIST += $(top_srcdir)/maint.mk
 
 ## end   gnulib module maintainer-makefile
 
+## begin gnulib module memchr
+
+
+EXTRA_DIST += memchr.c
+
+EXTRA_libgnu_la_SOURCES += memchr.c
+
+## end   gnulib module memchr
+
 ## begin gnulib module minmax
 
 libgnu_la_SOURCES += minmax.h
diff --git a/gl/m4/getpagesize.m4 b/gl/m4/getpagesize.m4
new file mode 100644
index 0000000000..0d07a3a53b
--- /dev/null
+++ b/gl/m4/getpagesize.m4
@@ -0,0 +1,29 @@
+# getpagesize.m4 serial 7
+dnl Copyright (C) 2002, 2004-2005, 2007 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_GETPAGESIZE],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_CHECK_FUNCS([getpagesize])
+  if test $ac_cv_func_getpagesize = no; then
+    HAVE_GETPAGESIZE=0
+    AC_CHECK_HEADERS([OS.h])
+    if test $ac_cv_header_OS_h = yes; then
+      HAVE_OS_H=1
+    fi
+    AC_CHECK_HEADERS([sys/param.h])
+    if test $ac_cv_header_sys_param_h = yes; then
+      HAVE_SYS_PARAM_H=1
+    fi
+  fi
+  case "$host_os" in
+    mingw*)
+      REPLACE_GETPAGESIZE=1
+      AC_LIBOBJ([getpagesize])
+      ;;
+  esac
+])
diff --git a/gl/m4/gnulib-comp.m4 b/gl/m4/gnulib-comp.m4
index 91cf94c439..fec57a6ca0 100644
--- a/gl/m4/gnulib-comp.m4
+++ b/gl/m4/gnulib-comp.m4
@@ -113,6 +113,7 @@ AC_SUBST([LTALLOCA])
   gl_SYS_SOCKET_MODULE_INDICATOR([listen])
   gl_FUNC_LSEEK
   gl_UNISTD_MODULE_INDICATOR([lseek])
+  gl_FUNC_MEMCHR
   gl_MINMAX
   gl_MULTIARCH
   gl_HEADER_NETDB
@@ -220,6 +221,8 @@ AC_SUBST([LTALLOCA])
   gl_COMMON
   gl_source_base='gl/tests'
   gl_FUNC_UNGETC_WORKS
+  gl_FUNC_GETPAGESIZE
+  gl_UNISTD_MODULE_INDICATOR([getpagesize])
   gl_FUNC_GETTIMEOFDAY
   AC_REQUIRE([gl_HEADER_SYS_SOCKET])
   if test "$ac_cv_header_winsock2_h" = yes; then
@@ -228,6 +231,9 @@ AC_SUBST([LTALLOCA])
   fi
   gl_SYS_IOCTL_MODULE_INDICATOR([ioctl])
   gl_MODULE_INDICATOR([ioctl])
+  gl_FUNC_MMAP_ANON
+  AC_CHECK_HEADERS_ONCE([sys/mman.h])
+  AC_CHECK_FUNCS_ONCE([mprotect])
   AC_CHECK_HEADERS_ONCE([unistd.h sys/wait.h])
   gt_TYPE_WCHAR_T
   gt_TYPE_WINT_T
@@ -371,6 +377,7 @@ AC_DEFUN([gl_FILE_LIST], [
   lib/intprops.h
   lib/listen.c
   lib/lseek.c
+  lib/memchr.c
   lib/minmax.h
   lib/netdb.in.h
   lib/netinet_in.in.h
@@ -432,6 +439,7 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/getaddrinfo.m4
   m4/getdelim.m4
   m4/getline.m4
+  m4/getpagesize.m4
   m4/getpass.m4
   m4/gettimeofday.m4
   m4/gnulib-common.m4
@@ -448,7 +456,9 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/lseek.m4
   m4/malloc.m4
   m4/manywarnings.m4
+  m4/memchr.m4
   m4/minmax.m4
+  m4/mmap-anon.m4
   m4/multiarch.m4
   m4/netdb_h.m4
   m4/netinet_in_h.m4
@@ -501,6 +511,7 @@ AC_DEFUN([gl_FILE_LIST], [
   tests/test-gettimeofday.c
   tests/test-lseek.c
   tests/test-lseek.sh
+  tests/test-memchr.c
   tests/test-netdb.c
   tests/test-netinet_in.c
   tests/test-perror.c
@@ -528,7 +539,9 @@ AC_DEFUN([gl_FILE_LIST], [
   tests/test-vc-list-files-cvs.sh
   tests/test-vc-list-files-git.sh
   tests/test-wchar.c
+  tests/zerosize-ptr.h
   tests=lib/dummy.c
+  tests=lib/getpagesize.c
   tests=lib/gettimeofday.c
   tests=lib/ioctl.c
   tests=lib/sys_ioctl.in.h
diff --git a/gl/m4/memchr.m4 b/gl/m4/memchr.m4
new file mode 100644
index 0000000000..53c5380281
--- /dev/null
+++ b/gl/m4/memchr.m4
@@ -0,0 +1,18 @@
+# memchr.m4 serial 5
+dnl Copyright (C) 2002, 2003, 2004, 2009 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_MEMCHR],
+[
+  AC_REPLACE_FUNCS([memchr])
+  if test $ac_cv_func_memchr = no; then
+    gl_PREREQ_MEMCHR
+  fi
+])
+
+# Prerequisites of lib/memchr.c.
+AC_DEFUN([gl_PREREQ_MEMCHR], [
+  AC_CHECK_HEADERS([bp-sym.h])
+])
diff --git a/gl/m4/mmap-anon.m4 b/gl/m4/mmap-anon.m4
new file mode 100644
index 0000000000..14b6270d28
--- /dev/null
+++ b/gl/m4/mmap-anon.m4
@@ -0,0 +1,59 @@
+# mmap-anon.m4 serial 8
+dnl Copyright (C) 2005, 2007, 2009 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+# Detect how mmap can be used to create anonymous (not file-backed) memory
+# mappings.
+# - On Linux, AIX, OSF/1, Solaris, Cygwin, Interix, Haiku, both MAP_ANONYMOUS
+#   and MAP_ANON exist and have the same value.
+# - On HP-UX, only MAP_ANONYMOUS exists.
+# - On MacOS X, FreeBSD, NetBSD, OpenBSD, only MAP_ANON exists.
+# - On IRIX, neither exists, and a file descriptor opened to /dev/zero must be
+#   used.
+
+AC_DEFUN([gl_FUNC_MMAP_ANON],
+[
+  dnl Work around a bug of AC_EGREP_CPP in autoconf-2.57.
+  AC_REQUIRE([AC_PROG_CPP])
+  AC_REQUIRE([AC_PROG_EGREP])
+
+  dnl Persuade glibc <sys/mman.h> to define MAP_ANONYMOUS.
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  # Check for mmap(). Don't use AC_FUNC_MMAP, because it checks too much: it
+  # fails on HP-UX 11, because MAP_FIXED mappings do not work. But this is
+  # irrelevant for anonymous mappings.
+  AC_CHECK_FUNC([mmap], [gl_have_mmap=yes], [gl_have_mmap=no])
+
+  # Try to allow MAP_ANONYMOUS.
+  gl_have_mmap_anonymous=no
+  if test $gl_have_mmap = yes; then
+    AC_MSG_CHECKING([for MAP_ANONYMOUS])
+    AC_EGREP_CPP([I cant identify this map.], [
+#include <sys/mman.h>
+#ifdef MAP_ANONYMOUS
+    I cant identify this map.
+#endif
+],
+      [gl_have_mmap_anonymous=yes])
+    if test $gl_have_mmap_anonymous != yes; then
+      AC_EGREP_CPP([I cant identify this map.], [
+#include <sys/mman.h>
+#ifdef MAP_ANON
+    I cant identify this map.
+#endif
+],
+        [AC_DEFINE([MAP_ANONYMOUS], [MAP_ANON],
+          [Define to a substitute value for mmap()'s MAP_ANONYMOUS flag.])
+         gl_have_mmap_anonymous=yes])
+    fi
+    AC_MSG_RESULT([$gl_have_mmap_anonymous])
+    if test $gl_have_mmap_anonymous = yes; then
+      AC_DEFINE([HAVE_MAP_ANONYMOUS], [1],
+        [Define to 1 if mmap()'s MAP_ANONYMOUS flag is available after including
+         config.h and <sys/mman.h>.])
+    fi
+  fi
+])
diff --git a/gl/memchr.c b/gl/memchr.c
new file mode 100644
index 0000000000..2253d2d651
--- /dev/null
+++ b/gl/memchr.c
@@ -0,0 +1,172 @@
+/* Copyright (C) 1991, 1993, 1996, 1997, 1999, 2000, 2003, 2004, 2006, 2008
+   Free Software Foundation, Inc.
+
+   Based on strlen implementation by Torbjorn Granlund (tege@sics.se),
+   with help from Dan Sahlin (dan@sics.se) and
+   commentary by Jim Blandy (jimb@ai.mit.edu);
+   adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu),
+   and implemented by Roland McGrath (roland@ai.mit.edu).
+
+NOTE: The canonical source of this file is maintained with the GNU C Library.
+Bugs can be reported to bug-glibc@prep.ai.mit.edu.
+
+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 the
+Free Software Foundation; either version 3 of the License, or any
+later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef _LIBC
+# include <config.h>
+#endif
+
+#include <string.h>
+
+#include <stddef.h>
+
+#if defined _LIBC
+# include <memcopy.h>
+#else
+# define reg_char char
+#endif
+
+#include <limits.h>
+
+#if HAVE_BP_SYM_H || defined _LIBC
+# include <bp-sym.h>
+#else
+# define BP_SYM(sym) sym
+#endif
+
+#undef __memchr
+#ifdef _LIBC
+# undef memchr
+#endif
+
+#ifndef weak_alias
+# define __memchr memchr
+#endif
+
+/* Search no more than N bytes of S for C.  */
+void *
+__memchr (void const *s, int c_in, size_t n)
+{
+  /* On 32-bit hardware, choosing longword to be a 32-bit unsigned
+     long instead of a 64-bit uintmax_t tends to give better
+     performance.  On 64-bit hardware, unsigned long is generally 64
+     bits already.  Change this typedef to experiment with
+     performance.  */
+  typedef unsigned long int longword;
+
+  const unsigned char *char_ptr;
+  const longword *longword_ptr;
+  longword repeated_one;
+  longword repeated_c;
+  unsigned reg_char c;
+
+  c = (unsigned char) c_in;
+
+  /* Handle the first few bytes by reading one byte at a time.
+     Do this until CHAR_PTR is aligned on a longword boundary.  */
+  for (char_ptr = (const unsigned char *) s;
+       n > 0 && (size_t) char_ptr % sizeof (longword) != 0;
+       --n, ++char_ptr)
+    if (*char_ptr == c)
+      return (void *) char_ptr;
+
+  longword_ptr = (const longword *) char_ptr;
+
+  /* All these elucidatory comments refer to 4-byte longwords,
+     but the theory applies equally well to any size longwords.  */
+
+  /* Compute auxiliary longword values:
+     repeated_one is a value which has a 1 in every byte.
+     repeated_c has c in every byte.  */
+  repeated_one = 0x01010101;
+  repeated_c = c | (c << 8);
+  repeated_c |= repeated_c << 16;
+  if (0xffffffffU < (longword) -1)
+    {
+      repeated_one |= repeated_one << 31 << 1;
+      repeated_c |= repeated_c << 31 << 1;
+      if (8 < sizeof (longword))
+	{
+	  size_t i;
+
+	  for (i = 64; i < sizeof (longword) * 8; i *= 2)
+	    {
+	      repeated_one |= repeated_one << i;
+	      repeated_c |= repeated_c << i;
+	    }
+	}
+    }
+
+  /* Instead of the traditional loop which tests each byte, we will test a
+     longword at a time.  The tricky part is testing if *any of the four*
+     bytes in the longword in question are equal to c.  We first use an xor
+     with repeated_c.  This reduces the task to testing whether *any of the
+     four* bytes in longword1 is zero.
+
+     We compute tmp =
+       ((longword1 - repeated_one) & ~longword1) & (repeated_one << 7).
+     That is, we perform the following operations:
+       1. Subtract repeated_one.
+       2. & ~longword1.
+       3. & a mask consisting of 0x80 in every byte.
+     Consider what happens in each byte:
+       - If a byte of longword1 is zero, step 1 and 2 transform it into 0xff,
+         and step 3 transforms it into 0x80.  A carry can also be propagated
+         to more significant bytes.
+       - If a byte of longword1 is nonzero, let its lowest 1 bit be at
+         position k (0 <= k <= 7); so the lowest k bits are 0.  After step 1,
+         the byte ends in a single bit of value 0 and k bits of value 1.
+         After step 2, the result is just k bits of value 1: 2^k - 1.  After
+         step 3, the result is 0.  And no carry is produced.
+     So, if longword1 has only non-zero bytes, tmp is zero.
+     Whereas if longword1 has a zero byte, call j the position of the least
+     significant zero byte.  Then the result has a zero at positions 0, ...,
+     j-1 and a 0x80 at position j.  We cannot predict the result at the more
+     significant bytes (positions j+1..3), but it does not matter since we
+     already have a non-zero bit at position 8*j+7.
+
+     So, the test whether any byte in longword1 is zero is equivalent to
+     testing whether tmp is nonzero.  */
+
+  while (n >= sizeof (longword))
+    {
+      longword longword1 = *longword_ptr ^ repeated_c;
+
+      if ((((longword1 - repeated_one) & ~longword1)
+	   & (repeated_one << 7)) != 0)
+	break;
+      longword_ptr++;
+      n -= sizeof (longword);
+    }
+
+  char_ptr = (const unsigned char *) longword_ptr;
+
+  /* At this point, we know that either n < sizeof (longword), or one of the
+     sizeof (longword) bytes starting at char_ptr is == c.  On little-endian
+     machines, we could determine the first such byte without any further
+     memory accesses, just by looking at the tmp result from the last loop
+     iteration.  But this does not work on big-endian machines.  Choose code
+     that works in both cases.  */
+
+  for (; n > 0; --n, ++char_ptr)
+    {
+      if (*char_ptr == c)
+	return (void *) char_ptr;
+    }
+
+  return NULL;
+}
+#ifdef weak_alias
+weak_alias (__memchr, BP_SYM (memchr))
+#endif
diff --git a/gl/tests/Makefile.am b/gl/tests/Makefile.am
index a37a580ca7..698e89bd3d 100644
--- a/gl/tests/Makefile.am
+++ b/gl/tests/Makefile.am
@@ -124,6 +124,15 @@ EXTRA_DIST += test-getline.c
 
 ## end   gnulib module getline-tests
 
+## begin gnulib module getpagesize
+
+
+EXTRA_DIST += getpagesize.c
+
+EXTRA_libtests_a_SOURCES += getpagesize.c
+
+## end   gnulib module getpagesize
+
 ## begin gnulib module gettimeofday
 
 
@@ -160,6 +169,14 @@ EXTRA_DIST += test-lseek.c test-lseek.sh
 
 ## end   gnulib module lseek-tests
 
+## begin gnulib module memchr-tests
+
+TESTS += test-memchr
+check_PROGRAMS += test-memchr
+EXTRA_DIST += test-memchr.c zerosize-ptr.h
+
+## end   gnulib module memchr-tests
+
 ## begin gnulib module netdb-tests
 
 TESTS += test-netdb
diff --git a/gl/tests/getpagesize.c b/gl/tests/getpagesize.c
new file mode 100644
index 0000000000..5498aa9483
--- /dev/null
+++ b/gl/tests/getpagesize.c
@@ -0,0 +1,39 @@
+/* getpagesize emulation for systems where it cannot be done in a C macro.
+
+   Copyright (C) 2007 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
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible and Martin Lambers.  */
+
+#include <config.h>
+
+/* Specification. */
+#include <unistd.h>
+
+/* This implementation is only for native Win32 systems.  */
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+
+int
+getpagesize (void)
+{
+  SYSTEM_INFO system_info;
+  GetSystemInfo (&system_info);
+  return system_info.dwPageSize;
+}
+
+#endif
diff --git a/gl/tests/test-memchr.c b/gl/tests/test-memchr.c
new file mode 100644
index 0000000000..1124f8b587
--- /dev/null
+++ b/gl/tests/test-memchr.c
@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2008-2009 Free Software Foundation
+ * Written by Eric Blake and Bruno Haible
+ *
+ * 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
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <string.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "zerosize-ptr.h"
+
+#define ASSERT(expr) \
+  do									     \
+    {									     \
+      if (!(expr))							     \
+	{								     \
+	  fprintf (stderr, "%s:%d: assertion failed\n", __FILE__, __LINE__); \
+	  fflush (stderr);						     \
+	  abort ();							     \
+	}								     \
+    }									     \
+  while (0)
+
+/* Calculating void * + int is not portable, so this wrapper converts
+   to char * to make the tests easier to write.  */
+#define MEMCHR (char *) memchr
+
+int
+main ()
+{
+  size_t n = 0x100000;
+  char *input = malloc (n);
+  ASSERT (input);
+
+  input[0] = 'a';
+  input[1] = 'b';
+  memset (input + 2, 'c', 1024);
+  memset (input + 1026, 'd', n - 1028);
+  input[n - 2] = 'e';
+  input[n - 1] = 'a';
+
+  /* Basic behavior tests.  */
+  ASSERT (MEMCHR (input, 'a', n) == input);
+
+  ASSERT (MEMCHR (input, 'a', 0) == NULL);
+  ASSERT (MEMCHR (zerosize_ptr (), 'a', 0) == NULL);
+
+  ASSERT (MEMCHR (input, 'b', n) == input + 1);
+  ASSERT (MEMCHR (input, 'c', n) == input + 2);
+  ASSERT (MEMCHR (input, 'd', n) == input + 1026);
+
+  ASSERT (MEMCHR (input + 1, 'a', n - 1) == input + n - 1);
+  ASSERT (MEMCHR (input + 1, 'e', n - 1) == input + n - 2);
+
+  ASSERT (MEMCHR (input, 'f', n) == NULL);
+  ASSERT (MEMCHR (input, '\0', n) == NULL);
+
+  /* Check that a very long haystack is handled quickly if the byte is
+     found near the beginning.  */
+  {
+    size_t repeat = 10000;
+    for (; repeat > 0; repeat--)
+      {
+	ASSERT (MEMCHR (input, 'c', n) == input + 2);
+      }
+  }
+
+  /* Alignment tests.  */
+  {
+    int i, j;
+    for (i = 0; i < 32; i++)
+      {
+	for (j = 0; j < 256; j++)
+	  input[i + j] = j;
+	for (j = 0; j < 256; j++)
+	  {
+	    ASSERT (MEMCHR (input + i, j, 256) == input + i + j);
+	  }
+      }
+  }
+
+  /* Check that memchr() does not read past the first occurrence of the
+     byte being searched.  See the Austin Group's clarification
+     <http://www.opengroup.org/austin/docs/austin_454.txt>.  */
+  {
+    char *page_boundary = (char *) zerosize_ptr ();
+
+    if (page_boundary != NULL)
+      {
+	int n;
+
+	for (n = 1; n <= 500; n++)
+	  {
+	    char *mem = page_boundary - n;
+	    memset (mem, 'X', n);
+	    ASSERT (MEMCHR (mem, 'U', n) == NULL);
+
+	    {
+	      int i;
+
+	      for (i = 0; i < n; i++)
+		{
+		  mem[i] = 'U';
+		  ASSERT (MEMCHR (mem, 'U', 4000) == mem + i);
+		  mem[i] = 'X';
+		}
+	    }
+	  }
+      }
+  }
+
+  free (input);
+
+  return 0;
+}
diff --git a/gl/tests/zerosize-ptr.h b/gl/tests/zerosize-ptr.h
new file mode 100644
index 0000000000..a38a2cf494
--- /dev/null
+++ b/gl/tests/zerosize-ptr.h
@@ -0,0 +1,68 @@
+/* Return a pointer to a zero-size object in memory.
+   Copyright (C) 2009 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
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* ISO C 99 does not allow memcmp(), memchr() etc. to be invoked with a NULL
+   argument.  Therefore this file produces a non-NULL pointer which cannot
+   be dereferenced, if possible.  */
+
+#include <stdlib.h>
+
+/* Test whether mmap() and mprotect() are available.
+   We don't use HAVE_MMAP, because AC_FUNC_MMAP would not define it on HP-UX.
+   HAVE_MPROTECT is not enough, because mingw does not have mmap() but has an
+   mprotect() function in libgcc.a.  */
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# include <fcntl.h>
+# include <unistd.h>
+# include <sys/types.h>
+# include <sys/mman.h>
+/* Define MAP_FILE when it isn't otherwise.  */
+# ifndef MAP_FILE
+#  define MAP_FILE 0
+# endif
+#endif
+
+/* Return a pointer to a zero-size object in memory (that is, actually, a
+   pointer to a page boundary where the previous page is readable and writable
+   and the next page is neither readable not writable), if possible.
+   Return NULL otherwise.  */
+
+static void *
+zerosize_ptr (void)
+{
+/* Use mmap and mprotect when they exist.  Don't test HAVE_MMAP, because it is
+   not defined on HP-UX 11 (since it does not support MAP_FIXED).  */
+#if HAVE_SYS_MMAN_H && HAVE_MPROTECT
+# if HAVE_MAP_ANONYMOUS
+  const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+  const int fd = -1;
+# else /* !HAVE_MAP_ANONYMOUS */
+  const int flags = MAP_FILE | MAP_PRIVATE;
+  int fd = open ("/dev/zero", O_RDONLY, 0666);
+  if (fd >= 0)
+# endif
+    {
+      int pagesize = getpagesize ();
+      char *two_pages =
+	(char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
+		       flags, fd, 0);
+      if (two_pages != (char *)(-1)
+	  && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
+	return two_pages + pagesize;
+    }
+#endif
+  return NULL;
+}