1 files changed, 260 insertions, 0 deletions
diff --git a/lib/di-set.c b/lib/di-set.c
new file mode 100644
index 0000000..f8d2558
--- /dev/null
+++ b/lib/di-set.c
@@ -0,0 +1,260 @@
+/* Set operations for device-inode pairs stored in a space-efficient manner.
+
+   Copyright 2009-2022 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 <https://www.gnu.org/licenses/>.  */
+
+/* written by Paul Eggert and Jim Meyering */
+
+#include <config.h>
+#include "di-set.h"
+
+#include "hash.h"
+#include "ino-map.h"
+
+#include <limits.h>
+#include <stdlib.h>
+
+/* The hash package hashes "void *", but this package wants to hash
+   integers.  Use integers that are as large as possible, but no
+   larger than void *, so that they can be cast to void * and back
+   without losing information.  */
+typedef size_t hashint;
+#define HASHINT_MAX ((hashint) -1)
+
+/* Integers represent inode numbers.  Integers in the range
+   1..(LARGE_INO_MIN-1) represent inode numbers directly.  (The hash
+   package does not work with null pointers, so inode 0 cannot be used
+   as a key.)  To find the representations of other inode numbers, map
+   them through INO_MAP.  */
+#define LARGE_INO_MIN (HASHINT_MAX / 2)
+
+/* Set operations for device-inode pairs stored in a space-efficient
+   manner.  Use a two-level hash table.  The top level hashes by
+   device number, as there are typically a small number of devices.
+   The lower level hashes by mapped inode numbers.  In the typical
+   case where the inode number is positive and small, the inode number
+   maps to itself, masquerading as a void * value; otherwise, its
+   value is the result of hashing the inode value through INO_MAP.  */
+
+/* A pair that maps a device number to a set of inode numbers.  */
+struct di_ent
+{
+  dev_t dev;
+  struct hash_table *ino_set;
+};
+
+/* A two-level hash table that manages and indexes these pairs.  */
+struct di_set
+{
+  /* Map device numbers to sets of inode number representatives.  */
+  struct hash_table *dev_map;
+
+  /* If nonnull, map large inode numbers to their small
+     representatives.  If null, there are no large inode numbers in
+     this set.  */
+  struct ino_map *ino_map;
+
+  /* Cache of the most recently allocated and otherwise-unused storage
+     for probing this table.  */
+  struct di_ent *probe;
+};
+
+/* Hash a device-inode-set entry.  */
+static size_t
+di_ent_hash (void const *x, size_t table_size)
+{
+  struct di_ent const *p = x;
+  dev_t dev = p->dev;
+
+  /* When DEV is wider than size_t, exclusive-OR the words of DEV into H.
+     This avoids loss of info, without applying % to the wider type,
+     which could be quite slow on some systems.  */
+  size_t h = dev;
+  unsigned int i;
+  unsigned int n_words = sizeof dev / sizeof h + (sizeof dev % sizeof h != 0);
+  for (i = 1; i < n_words; i++)
+    h ^= dev >> CHAR_BIT * sizeof h * i;
+
+  return h % table_size;
+}
+
+/* Return true if two device-inode-set entries are the same.  */
+static bool
+di_ent_compare (void const *x, void const *y)
+{
+  struct di_ent const *a = x;
+  struct di_ent const *b = y;
+  return a->dev == b->dev;
+}
+
+/* Free a device-inode-set entry.  */
+static void
+di_ent_free (void *v)
+{
+  struct di_ent *a = v;
+  hash_free (a->ino_set);
+  free (a);
+}
+
+/* Create a set of device-inode pairs.  Return NULL on allocation failure.  */
+struct di_set *
+di_set_alloc (void)
+{
+  struct di_set *dis = malloc (sizeof *dis);
+  if (dis)
+    {
+      enum { INITIAL_DEV_MAP_SIZE = 11 };
+      dis->dev_map = hash_initialize (INITIAL_DEV_MAP_SIZE, NULL,
+                                      di_ent_hash, di_ent_compare,
+                                      di_ent_free);
+      if (! dis->dev_map)
+        {
+          free (dis);
+          return NULL;
+        }
+      dis->ino_map = NULL;
+      dis->probe = NULL;
+    }
+
+  return dis;
+}
+
+/* Free a set of device-inode pairs.  */
+void
+di_set_free (struct di_set *dis)
+{
+  hash_free (dis->dev_map);
+  if (dis->ino_map)
+    ino_map_free (dis->ino_map);
+  free (dis->probe);
+  free (dis);
+}
+
+/* Hash an encoded inode number I.  */
+static size_t
+di_ino_hash (void const *i, size_t table_size)
+{
+  return (hashint) i % table_size;
+}
+
+/* Using the DIS table, map a device to a hash table that represents
+   a set of inode numbers.  Return NULL on error.  */
+static struct hash_table *
+map_device (struct di_set *dis, dev_t dev)
+{
+  /* Find space for the probe, reusing the cache if available.  */
+  struct di_ent *ent;
+  struct di_ent *probe = dis->probe;
+  if (probe)
+    {
+      /* If repeating a recent query, return the cached result.   */
+      if (probe->dev == dev)
+        return probe->ino_set;
+    }
+  else
+    {
+      dis->probe = probe = malloc (sizeof *probe);
+      if (! probe)
+        return NULL;
+    }
+
+  /* Probe for the device.  */
+  probe->dev = dev;
+  ent = hash_insert (dis->dev_map, probe);
+  if (! ent)
+    return NULL;
+
+  if (ent != probe)
+    {
+      /* Use the existing entry.  */
+      probe->ino_set = ent->ino_set;
+    }
+  else
+    {
+      enum { INITIAL_INO_SET_SIZE = 1021 };
+
+      /* Prepare to allocate a new probe next time; this one is in use.  */
+      dis->probe = NULL;
+
+      /* DEV is new; allocate an inode set for it.  */
+      probe->ino_set = hash_initialize (INITIAL_INO_SET_SIZE, NULL,
+                                        di_ino_hash, NULL, NULL);
+    }
+
+  return probe->ino_set;
+}
+
+/* Using the DIS table, map an inode number to a mapped value.
+   Return INO_MAP_INSERT_FAILURE on error.  */
+static hashint
+map_inode_number (struct di_set *dis, ino_t ino)
+{
+  if (0 < ino && ino < LARGE_INO_MIN)
+    return ino;
+
+  if (! dis->ino_map)
+    {
+      dis->ino_map = ino_map_alloc (LARGE_INO_MIN);
+      if (! dis->ino_map)
+        return INO_MAP_INSERT_FAILURE;
+    }
+
+  return ino_map_insert (dis->ino_map, ino);
+}
+
+/* Attempt to insert the DEV,INO pair into the set DIS.
+   If it matches a pair already in DIS, keep that pair and return 0.
+   Otherwise, if insertion is successful, return 1.
+   Upon any failure return -1.  */
+int
+di_set_insert (struct di_set *dis, dev_t dev, ino_t ino)
+{
+  hashint i;
+
+  /* Map the device number to a set of inodes.  */
+  struct hash_table *ino_set = map_device (dis, dev);
+  if (! ino_set)
+    return -1;
+
+  /* Map the inode number to a small representative I.  */
+  i = map_inode_number (dis, ino);
+  if (i == INO_MAP_INSERT_FAILURE)
+    return -1;
+
+  /* Put I into the inode set.  */
+  return hash_insert_if_absent (ino_set, (void const *) i, NULL);
+}
+
+/* Look up the DEV,INO pair in the set DIS.
+   If found, return 1; if not found, return 0.
+   Upon any failure return -1.  */
+int
+di_set_lookup (struct di_set *dis, dev_t dev, ino_t ino)
+{
+  hashint i;
+
+  /* Map the device number to a set of inodes.  */
+  struct hash_table *ino_set = map_device (dis, dev);
+  if (! ino_set)
+    return -1;
+
+  /* Map the inode number to a small representative I.  */
+  i = map_inode_number (dis, ino);
+  if (i == INO_MAP_INSERT_FAILURE)
+    return -1;
+
+  /* Perform the look-up.  */
+  return !!hash_lookup (ino_set, (void const *) i);
+}