new file mode 100644
--- /dev/null
+++ b/lib/utimecmp.c
@@ -0,0 +1,340 @@
+/* utimecmp.c -- compare file time stamps
+
+   Copyright (C) 2004 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 2, 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, write to the Free Software Foundation,
+   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+/* Written by Paul Eggert.  */
+
+#if HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "utimecmp.h"
+
+#if HAVE_INTTYPES_H
+# include <inttypes.h>
+#endif
+#if HAVE_STDINT_H
+# include <stdint.h>
+#endif
+
+#include <limits.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include "hash.h"
+#include "timespec.h"
+#include "utimens.h"
+#include "xalloc.h"
+
+/* Verify a requirement at compile-time (unlike assert, which is runtime).  */
+#define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
+
+#ifndef MAX
+# define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
+#ifndef SIZE_MAX
+# define SIZE_MAX ((size_t) -1)
+#endif
+
+/* The extra casts work around common compiler bugs.  */
+#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
+/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
+   It is necessary at least when t == time_t.  */
+#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
+			      ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
+#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
+
+enum { BILLION = 1000 * 1000 * 1000 };
+
+/* Best possible resolution that utimens can set and stat can return,
+   due to system-call limitations.  It must be a power of 10 that is
+   no greater than 1 billion.  */
+#if HAVE_WORKING_UTIMES && defined ST_MTIM_NSEC
+enum { SYSCALL_RESOLUTION = 1000 };
+#else
+enum { SYSCALL_RESOLUTION = BILLION };
+#endif
+
+/* Describe a file system and its time stamp resolution in nanoseconds.  */
+struct fs_res
+{
+  /* Device number of file system.  */
+  dev_t dev;
+
+  /* An upper bound on the time stamp resolution of this file system,
+     ignoring any resolution that cannot be set via utimens.  It is
+     represented by an integer count of nanoseconds.  It must be
+     either 2 billion, or a power of 10 that is no greater than a
+     billion and is no less than SYSCALL_RESOLUTION.  */
+  int resolution;
+
+  /* True if RESOLUTION is known to be exact, and is not merely an
+     upper bound on the true resolution.  */
+  bool exact;
+};
+
+/* Hash some device info.  */
+static size_t
+dev_info_hash (void const *x, size_t table_size)
+{
+  struct fs_res const *p = x;
+
+  /* Beware signed arithmetic gotchas.  */
+  if (TYPE_SIGNED (dev_t) && SIZE_MAX < MAX (INT_MAX, TYPE_MAXIMUM (dev_t)))
+    {
+      uintmax_t dev = p->dev;
+      return dev % table_size;
+    }
+
+  return p->dev % table_size;
+}
+
+/* Compare two dev_info structs.  */
+static bool
+dev_info_compare (void const *x, void const *y)
+{
+  struct fs_res const *a = x;
+  struct fs_res const *b = y;
+  return a->dev == b->dev;
+}
+
+/* Return -1, 0, 1 based on whether the destination file (with name
+   DST_NAME and status DST_STAT) is older than SRC_STAT, the same age
+   as SRC_STAT, or newer than SRC_STAT, respectively.
+
+   If OPTIONS & UTIMECMP_TRUNCATE_SOURCE, do the comparison after SRC is
+   converted to the destination's timestamp resolution as filtered through
+   utimens.  In this case, return -2 if the exact answer cannot be
+   determined; this can happen only if the time stamps are very close and
+   there is some trouble accessing the file system (e.g., the user does not
+   have permission to futz with the destination's time stamps).  */
+
+int
+utimecmp (char const *dst_name,
+	  struct stat const *dst_stat,
+	  struct stat const *src_stat,
+	  int options)
+{
+  /* Things to watch out for:
+
+     The code uses a static hash table internally and is not safe in the
+     presence of signals, multiple threads, etc.
+
+     int and long int might be 32 bits.  Many of the calculations store
+     numbers up to 2 billion, and multiply by 10; they have to avoid
+     multiplying 2 billion by 10, as this exceeds 32-bit capabilities.
+
+     time_t might be unsigned.  */
+
+  verify (time_t_is_integer, (time_t) 0.5 == 0);
+  verify (twos_complement_arithmetic, -1 == ~1 + 1);
+
+  /* Destination and source time stamps.  */
+  time_t dst_s = dst_stat->st_mtime;
+  time_t src_s = src_stat->st_mtime;
+  int dst_ns = TIMESPEC_NS (dst_stat->st_mtim);
+  int src_ns = TIMESPEC_NS (src_stat->st_mtim);
+
+  if (options & UTIMECMP_TRUNCATE_SOURCE)
+    {
+      /* Look up the time stamp resolution for the destination device.  */
+
+      /* Hash table for devices.  */
+      static Hash_table *ht;
+
+      /* Information about the destination file system.  */
+      static struct fs_res *new_dst_res;
+      struct fs_res *dst_res;
+
+      /* Time stamp resolution in nanoseconds.  */
+      int res;
+
+      if (! ht)
+	ht = hash_initialize (16, NULL, dev_info_hash, dev_info_compare, free);
+      if (! new_dst_res)
+	{
+	  new_dst_res = xmalloc (sizeof *new_dst_res);
+	  new_dst_res->resolution = 2 * BILLION;
+	  new_dst_res->exact = false;
+	}
+      new_dst_res->dev = dst_stat->st_dev;
+      dst_res = hash_insert (ht, new_dst_res);
+      if (! dst_res)
+	xalloc_die ();
+
+      if (dst_res == new_dst_res)
+	{
+	  /* NEW_DST_RES is now in use in the hash table, so allocate a
+	     new entry next time.  */
+	  new_dst_res = NULL;
+	}
+
+      res = dst_res->resolution;
+
+      if (! dst_res->exact)
+	{
+	  /* This file system's resolution is not known exactly.
+	     Deduce it, and store the result in the hash table.  */
+
+	  time_t dst_a_s = dst_stat->st_atime;
+	  time_t dst_c_s = dst_stat->st_ctime;
+	  time_t dst_m_s = dst_s;
+	  int dst_a_ns = TIMESPEC_NS (dst_stat->st_atim);
+	  int dst_c_ns = TIMESPEC_NS (dst_stat->st_ctim);
+	  int dst_m_ns = dst_ns;
+
+	  /* Set RES to an upper bound on the file system resolution
+	     (after truncation due to SYSCALL_RESOLUTION) by inspecting
+	     the atime, ctime and mtime of the existing destination.
+	     We don't know of any file system that stores atime or
+	     ctime with a higher precision than mtime, so it's valid to
+	     look at them too.  */
+	  {
+	    bool odd_second = (dst_a_s | dst_c_s | dst_m_s) & 1;
+
+	    if (SYSCALL_RESOLUTION == BILLION)
+	      {
+		if (odd_second | dst_a_ns | dst_c_ns | dst_m_ns)
+		  res = BILLION;
+	      }
+	    else
+	      {
+		int a = dst_a_ns;
+		int c = dst_c_ns;
+		int m = dst_m_ns;
+
+		/* Write it this way to avoid mistaken GCC warning
+		   about integer overflow in constant expression.  */
+		int SR10 = SYSCALL_RESOLUTION;  SR10 *= 10;
+
+		if ((a % SR10 | c % SR10 | m % SR10) != 0)
+		  res = SYSCALL_RESOLUTION;
+		else
+		  for (res = SR10, a /= SR10, c /= SR10, m /= SR10;
+		       (res < dst_res->resolution
+			&& (a % 10 | c % 10 | m % 10) == 0);
+		       res *= 10, a /= 10, c /= 10, m /= 10)
+		    if (res == BILLION)
+		      {
+			if (! odd_second)
+			  res *= 2;
+			break;
+		      }
+	      }
+
+	    dst_res->resolution = res;
+	  }
+
+	  if (SYSCALL_RESOLUTION < res)
+	    {
+	      struct timespec timespec[2];
+	      struct stat dst_status;
+
+	      /* Ignore source time stamp information that must necessarily
+		 be lost when filtered through utimens.  */
+	      src_ns -= src_ns % SYSCALL_RESOLUTION;
+
+	      /* If the time stamps disagree widely enough, there's no need
+		 to interrogate the file system to deduce the exact time
+		 stamp resolution; return the answer directly.  */
+	      {
+		time_t s = src_s & ~ (res == 2 * BILLION);
+		if (src_s < dst_s || (src_s == dst_s && src_ns <= dst_ns))
+		  return 1;
+		if (dst_s < s
+		    || (dst_s == s && dst_ns < src_ns - src_ns % res))
+		  return -1;
+	      }
+
+	      /* Determine the actual time stamp resolution for the
+		 destination file system (after truncation due to
+		 SYSCALL_RESOLUTION) by setting the access time stamp of the
+		 destination to the existing access time, except with
+		 trailing nonzero digits.  */
+
+	      timespec[0].tv_sec = dst_a_s;
+	      timespec[0].tv_nsec = dst_a_ns;
+	      timespec[1].tv_sec = dst_m_s | (res == 2 * BILLION);
+	      timespec[1].tv_nsec = dst_m_ns + res / 9;
+
+	      /* Set the modification time.  But don't try to set the
+		 modification time of symbolic links; on many hosts this sets
+		 the time of the pointed-to file.  */
+	      if (S_ISLNK (dst_stat->st_mode)
+		  || utimens (dst_name, timespec) != 0)
+		return -2;
+
+	      /* Read the modification time that was set.  It's safe to call
+		 'stat' here instead of worrying about 'lstat'; either the
+		 caller used 'stat', or the caller used 'lstat' and found
+		 something other than a symbolic link.  */
+	      {
+		int stat_result = stat (dst_name, &dst_status);
+
+		if (stat_result
+		    | (dst_status.st_mtime ^ dst_m_s)
+		    | (TIMESPEC_NS (dst_status.st_mtim) ^ dst_m_ns))
+		  {
+		    /* The modification time changed, or we can't tell whether
+		       it changed.  Change it back as best we can.  */
+		    timespec[1].tv_sec = dst_m_s;
+		    timespec[1].tv_nsec = dst_m_ns;
+		    utimens (dst_name, timespec);
+		  }
+
+		if (stat_result != 0)
+		  return -2;
+	      }
+
+	      /* Determine the exact resolution from the modification time
+		 that was read back.  */
+	      {
+		int old_res = res;
+		int a = (BILLION * (dst_status.st_mtime & 1)
+			 + TIMESPEC_NS (dst_status.st_mtim));
+
+		res = SYSCALL_RESOLUTION;
+
+		for (a /= res; a % 10 != 0; a /= 10)
+		  {
+		    if (res == BILLION)
+		      {
+			res *= 2;
+			break;
+		      }
+		    res *= 10;
+		    if (res == old_res)
+		      break;
+		  }
+	      }
+	    }
+
+	  dst_res->resolution = res;
+	  dst_res->exact = true;
+	}
+
+      /* Truncate the source's time stamp according to the resolution.  */
+      src_s &= ~ (res == 2 * BILLION);
+      src_ns -= src_ns % res;
+    }
+
+  /* Compare the time stamps and return -1, 0, 1 accordingly.  */
+  return (dst_s < src_s ? -1
+	  : dst_s > src_s ? 1
+	  : dst_ns < src_ns ? -1
+	  : dst_ns > src_ns);
+}

new file mode 100644
--- /dev/null
+++ b/lib/utimecmp.h
@@ -0,0 +1,38 @@
+/* utimecmp.h -- compare file time stamps
+
+   Copyright (C) 2004 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 2, 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, write to the Free Software Foundation,
+   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+/* Written by Paul Eggert.  */
+
+#ifndef UTIMECMP_H
+#define UTIMECMP_H 1
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+/* Options for utimecmp.  */
+enum
+{
+  /* Before comparing, truncate the source time stamp to the
+     resolution of the destination file system and to the resolution
+     of utimens.  */
+  UTIMECMP_TRUNCATE_SOURCE = 1
+};
+
+int utimecmp (char const *, struct stat const *, struct stat const *, int);
+
+#endif

new file mode 100644
--- /dev/null
+++ b/m4/utimecmp.m4
@@ -0,0 +1,14 @@
+dnl Copyright (C) 2004 Free Software Foundation, Inc.
+dnl This file is free software, distributed under the terms of the GNU
+dnl General Public License.  As a special exception to the GNU General
+dnl Public License, this file may be distributed as part of a program
+dnl that contains a configuration script generated by Autoconf, under
+dnl the same distribution terms as the rest of that program.
+
+AC_DEFUN([gl_UTIMECMP],
+[
+  dnl Prerequisites of lib/utimecmp.c.
+  AC_REQUIRE([gl_TIMESPEC])
+  AC_REQUIRE([gl_FUNC_UTIMES])
+  :
+])

new file mode 100644
--- /dev/null
+++ b/modules/utimecmp
@@ -0,0 +1,26 @@
+Description:
+compare file time stamps
+
+Files:
+lib/utimecmp.h
+lib/utimecmp.c
+m4/utimecmp.m4
+
+Depends-on:
+hash
+timespec
+utimens
+xalloc
+
+configure.ac:
+gl_UTIMECMP
+
+Makefile.am:
+lib_SOURCES += utimecmp.h utimecmp.c
+
+Include:
+"utimecmp.h"
+
+Maintainer:
+Paul Eggert, Jim Meyering
+