--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2007-09-27  Jim Meyering  <jim@meyering.net>
 
+	New module, file-set.
+	* modules/file-set: Define it.
+	* lib/file-set.c, lib/file-set.h: Implement.
+
 	New module, hash-triple.
 	* modules/hash-triple: Define it.
 	* lib/hash-triple.c, lib/hash-triple.h: Implement.

new file mode 100644
--- /dev/null
+++ b/lib/file-set.c
@@ -0,0 +1,75 @@
+/* Specialized functions to manipulate a set of files.
+   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 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* written by Jim Meyering */
+
+#include <config.h>
+#include "file-set.h"
+
+#include "hash-triple.h"
+#include "xalloc.h"
+
+/* Record file, FILE, and dev/ino from *STATS, in the hash table, HT.
+   If HT is NULL, return immediately.
+   If memory allocation fails, exit immediately.  */
+void
+record_file (Hash_table *ht, char const *file, struct stat const *stats)
+{
+  struct F_triple *ent;
+
+  if (ht == NULL)
+    return;
+
+  ent = xmalloc (sizeof *ent);
+  ent->name = xstrdup (file);
+  ent->st_ino = stats->st_ino;
+  ent->st_dev = stats->st_dev;
+
+  {
+    struct F_triple *ent_from_table = hash_insert (ht, ent);
+    if (ent_from_table == NULL)
+      {
+	/* Insertion failed due to lack of memory.  */
+	xalloc_die ();
+      }
+
+    if (ent_from_table != ent)
+      {
+	/* There was alread a matching entry in the table, so ENT was
+	   not inserted.  Free it.  */
+	triple_free (ent);
+      }
+  }
+}
+
+/* Return true if there is an entry in hash table, HT,
+   for the file described by FILE and STATS.  */
+bool
+seen_file (Hash_table const *ht, char const *file,
+	   struct stat const *stats)
+{
+  struct F_triple new_ent;
+
+  if (ht == NULL)
+    return false;
+
+  new_ent.name = (char *) file;
+  new_ent.st_ino = stats->st_ino;
+  new_ent.st_dev = stats->st_dev;
+
+  return !!hash_lookup (ht, &new_ent);
+}

new file mode 100644
--- /dev/null
+++ b/lib/file-set.h
@@ -0,0 +1,12 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <stdbool.h>
+
+#include "hash.h"
+
+extern void record_file (Hash_table *ht, char const *file,
+			 struct stat const *stats)
+  __attribute__((nonnull(2, 3)));
+
+extern bool seen_file (Hash_table const *ht, char const *file,
+		       struct stat const *stats);

new file mode 100644
--- /dev/null
+++ b/modules/file-set
@@ -0,0 +1,27 @@
+Description:
+Very specialized set-of-files code.
+
+Files:
+lib/file-set.c
+lib/file-set.h
+
+Depends-on:
+hash
+hash-triple
+stdbool
+xalloc
+xalloc-die
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += file-set.c
+
+Include:
+"file-set.h"
+
+License:
+GPL
+
+Maintainer:
+Jim Meyering