Adding upstream version 2.9.4.upstream/2.9.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1225 insertions, 0 deletions

diff --git a/gl/lib/hash.c b/gl/lib/hash.c
new file mode 100644
index 0000000..7aaf106
--- /dev/null
+++ b/gl/lib/hash.c
@@ -0,0 +1,1225 @@
+/* hash - hashing table processing.
+
+   Copyright (C) 1998-2004, 2006-2007, 2009-2020 Free Software Foundation, Inc.
+
+   Written by Jim Meyering, 1992.
+
+   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/>.  */
+
+/* A generic hash table package.  */
+
+/* Define USE_OBSTACK to 1 if you want the allocator to use obstacks instead
+   of malloc.  If you change USE_OBSTACK, you have to recompile!  */
+
+#include <config.h>
+
+#include "hash.h"
+
+#include "bitrotate.h"
+#include "xalloc-oversized.h"
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if USE_OBSTACK
+# include "obstack.h"
+# ifndef obstack_chunk_alloc
+#  define obstack_chunk_alloc malloc
+# endif
+# ifndef obstack_chunk_free
+#  define obstack_chunk_free free
+# endif
+#endif
+
+struct hash_entry
+  {
+    void *data;
+    struct hash_entry *next;
+  };
+
+struct hash_table
+  {
+    /* The array of buckets starts at BUCKET and extends to BUCKET_LIMIT-1,
+       for a possibility of N_BUCKETS.  Among those, N_BUCKETS_USED buckets
+       are not empty, there are N_ENTRIES active entries in the table.  */
+    struct hash_entry *bucket;
+    struct hash_entry const *bucket_limit;
+    size_t n_buckets;
+    size_t n_buckets_used;
+    size_t n_entries;
+
+    /* Tuning arguments, kept in a physically separate structure.  */
+    const Hash_tuning *tuning;
+
+    /* Three functions are given to 'hash_initialize', see the documentation
+       block for this function.  In a word, HASHER randomizes a user entry
+       into a number up from 0 up to some maximum minus 1; COMPARATOR returns
+       true if two user entries compare equally; and DATA_FREER is the cleanup
+       function for a user entry.  */
+    Hash_hasher hasher;
+    Hash_comparator comparator;
+    Hash_data_freer data_freer;
+
+    /* A linked list of freed struct hash_entry structs.  */
+    struct hash_entry *free_entry_list;
+
+#if USE_OBSTACK
+    /* Whenever obstacks are used, it is possible to allocate all overflowed
+       entries into a single stack, so they all can be freed in a single
+       operation.  It is not clear if the speedup is worth the trouble.  */
+    struct obstack entry_stack;
+#endif
+  };
+
+/* A hash table contains many internal entries, each holding a pointer to
+   some user-provided data (also called a user entry).  An entry indistinctly
+   refers to both the internal entry and its associated user entry.  A user
+   entry contents may be hashed by a randomization function (the hashing
+   function, or just "hasher" for short) into a number (or "slot") between 0
+   and the current table size.  At each slot position in the hash table,
+   starts a linked chain of entries for which the user data all hash to this
+   slot.  A bucket is the collection of all entries hashing to the same slot.
+
+   A good "hasher" function will distribute entries rather evenly in buckets.
+   In the ideal case, the length of each bucket is roughly the number of
+   entries divided by the table size.  Finding the slot for a data is usually
+   done in constant time by the "hasher", and the later finding of a precise
+   entry is linear in time with the size of the bucket.  Consequently, a
+   larger hash table size (that is, a larger number of buckets) is prone to
+   yielding shorter chains, *given* the "hasher" function behaves properly.
+
+   Long buckets slow down the lookup algorithm.  One might use big hash table
+   sizes in hope to reduce the average length of buckets, but this might
+   become inordinate, as unused slots in the hash table take some space.  The
+   best bet is to make sure you are using a good "hasher" function (beware
+   that those are not that easy to write! :-), and to use a table size
+   larger than the actual number of entries.  */
+
+/* If an insertion makes the ratio of nonempty buckets to table size larger
+   than the growth threshold (a number between 0.0 and 1.0), then increase
+   the table size by multiplying by the growth factor (a number greater than
+   1.0).  The growth threshold defaults to 0.8, and the growth factor
+   defaults to 1.414, meaning that the table will have doubled its size
+   every second time 80% of the buckets get used.  */
+#define DEFAULT_GROWTH_THRESHOLD 0.8f
+#define DEFAULT_GROWTH_FACTOR 1.414f
+
+/* If a deletion empties a bucket and causes the ratio of used buckets to
+   table size to become smaller than the shrink threshold (a number between
+   0.0 and 1.0), then shrink the table by multiplying by the shrink factor (a
+   number greater than the shrink threshold but smaller than 1.0).  The shrink
+   threshold and factor default to 0.0 and 1.0, meaning that the table never
+   shrinks.  */
+#define DEFAULT_SHRINK_THRESHOLD 0.0f
+#define DEFAULT_SHRINK_FACTOR 1.0f
+
+/* Use this to initialize or reset a TUNING structure to
+   some sensible values. */
+static const Hash_tuning default_tuning =
+  {
+    DEFAULT_SHRINK_THRESHOLD,
+    DEFAULT_SHRINK_FACTOR,
+    DEFAULT_GROWTH_THRESHOLD,
+    DEFAULT_GROWTH_FACTOR,
+    false
+  };
+
+/* Information and lookup.  */
+
+/* The following few functions provide information about the overall hash
+   table organization: the number of entries, number of buckets and maximum
+   length of buckets.  */
+
+/* Return the number of buckets in the hash table.  The table size, the total
+   number of buckets (used plus unused), or the maximum number of slots, are
+   the same quantity.  */
+
+size_t
+hash_get_n_buckets (const Hash_table *table)
+{
+  return table->n_buckets;
+}
+
+/* Return the number of slots in use (non-empty buckets).  */
+
+size_t
+hash_get_n_buckets_used (const Hash_table *table)
+{
+  return table->n_buckets_used;
+}
+
+/* Return the number of active entries.  */
+
+size_t
+hash_get_n_entries (const Hash_table *table)
+{
+  return table->n_entries;
+}
+
+/* Return the length of the longest chain (bucket).  */
+
+size_t
+hash_get_max_bucket_length (const Hash_table *table)
+{
+  struct hash_entry const *bucket;
+  size_t max_bucket_length = 0;
+
+  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+    {
+      if (bucket->data)
+        {
+          struct hash_entry const *cursor = bucket;
+          size_t bucket_length = 1;
+
+          while (cursor = cursor->next, cursor)
+            bucket_length++;
+
+          if (bucket_length > max_bucket_length)
+            max_bucket_length = bucket_length;
+        }
+    }
+
+  return max_bucket_length;
+}
+
+/* Do a mild validation of a hash table, by traversing it and checking two
+   statistics.  */
+
+bool
+hash_table_ok (const Hash_table *table)
+{
+  struct hash_entry const *bucket;
+  size_t n_buckets_used = 0;
+  size_t n_entries = 0;
+
+  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+    {
+      if (bucket->data)
+        {
+          struct hash_entry const *cursor = bucket;
+
+          /* Count bucket head.  */
+          n_buckets_used++;
+          n_entries++;
+
+          /* Count bucket overflow.  */
+          while (cursor = cursor->next, cursor)
+            n_entries++;
+        }
+    }
+
+  if (n_buckets_used == table->n_buckets_used && n_entries == table->n_entries)
+    return true;
+
+  return false;
+}
+
+void
+hash_print_statistics (const Hash_table *table, FILE *stream)
+{
+  size_t n_entries = hash_get_n_entries (table);
+  size_t n_buckets = hash_get_n_buckets (table);
+  size_t n_buckets_used = hash_get_n_buckets_used (table);
+  size_t max_bucket_length = hash_get_max_bucket_length (table);
+
+  fprintf (stream, "# entries:         %lu\n", (unsigned long int) n_entries);
+  fprintf (stream, "# buckets:         %lu\n", (unsigned long int) n_buckets);
+  fprintf (stream, "# buckets used:    %lu (%.2f%%)\n",
+           (unsigned long int) n_buckets_used,
+           (100.0 * n_buckets_used) / n_buckets);
+  fprintf (stream, "max bucket length: %lu\n",
+           (unsigned long int) max_bucket_length);
+}
+
+/* Hash KEY and return a pointer to the selected bucket.
+   If TABLE->hasher misbehaves, abort.  */
+static struct hash_entry *
+safe_hasher (const Hash_table *table, const void *key)
+{
+  size_t n = table->hasher (key, table->n_buckets);
+  if (! (n < table->n_buckets))
+    abort ();
+  return table->bucket + n;
+}
+
+/* If ENTRY matches an entry already in the hash table, return the
+   entry from the table.  Otherwise, return NULL.  */
+
+void *
+hash_lookup (const Hash_table *table, const void *entry)
+{
+  struct hash_entry const *bucket = safe_hasher (table, entry);
+  struct hash_entry const *cursor;
+
+  if (bucket->data == NULL)
+    return NULL;
+
+  for (cursor = bucket; cursor; cursor = cursor->next)
+    if (entry == cursor->data || table->comparator (entry, cursor->data))
+      return cursor->data;
+
+  return NULL;
+}
+
+/* Walking.  */
+
+/* The functions in this page traverse the hash table and process the
+   contained entries.  For the traversal to work properly, the hash table
+   should not be resized nor modified while any particular entry is being
+   processed.  In particular, entries should not be added, and an entry
+   may be removed only if there is no shrink threshold and the entry being
+   removed has already been passed to hash_get_next.  */
+
+/* Return the first data in the table, or NULL if the table is empty.  */
+
+void *
+hash_get_first (const Hash_table *table)
+{
+  struct hash_entry const *bucket;
+
+  if (table->n_entries == 0)
+    return NULL;
+
+  for (bucket = table->bucket; ; bucket++)
+    if (! (bucket < table->bucket_limit))
+      abort ();
+    else if (bucket->data)
+      return bucket->data;
+}
+
+/* Return the user data for the entry following ENTRY, where ENTRY has been
+   returned by a previous call to either 'hash_get_first' or 'hash_get_next'.
+   Return NULL if there are no more entries.  */
+
+void *
+hash_get_next (const Hash_table *table, const void *entry)
+{
+  struct hash_entry const *bucket = safe_hasher (table, entry);
+  struct hash_entry const *cursor;
+
+  /* Find next entry in the same bucket.  */
+  cursor = bucket;
+  do
+    {
+      if (cursor->data == entry && cursor->next)
+        return cursor->next->data;
+      cursor = cursor->next;
+    }
+  while (cursor != NULL);
+
+  /* Find first entry in any subsequent bucket.  */
+  while (++bucket < table->bucket_limit)
+    if (bucket->data)
+      return bucket->data;
+
+  /* None found.  */
+  return NULL;
+}
+
+/* Fill BUFFER with pointers to active user entries in the hash table, then
+   return the number of pointers copied.  Do not copy more than BUFFER_SIZE
+   pointers.  */
+
+size_t
+hash_get_entries (const Hash_table *table, void **buffer,
+                  size_t buffer_size)
+{
+  size_t counter = 0;
+  struct hash_entry const *bucket;
+  struct hash_entry const *cursor;
+
+  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+    {
+      if (bucket->data)
+        {
+          for (cursor = bucket; cursor; cursor = cursor->next)
+            {
+              if (counter >= buffer_size)
+                return counter;
+              buffer[counter++] = cursor->data;
+            }
+        }
+    }
+
+  return counter;
+}
+
+/* Call a PROCESSOR function for each entry of a hash table, and return the
+   number of entries for which the processor function returned success.  A
+   pointer to some PROCESSOR_DATA which will be made available to each call to
+   the processor function.  The PROCESSOR accepts two arguments: the first is
+   the user entry being walked into, the second is the value of PROCESSOR_DATA
+   as received.  The walking continue for as long as the PROCESSOR function
+   returns nonzero.  When it returns zero, the walking is interrupted.  */
+
+size_t
+hash_do_for_each (const Hash_table *table, Hash_processor processor,
+                  void *processor_data)
+{
+  size_t counter = 0;
+  struct hash_entry const *bucket;
+  struct hash_entry const *cursor;
+
+  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+    {
+      if (bucket->data)
+        {
+          for (cursor = bucket; cursor; cursor = cursor->next)
+            {
+              if (! processor (cursor->data, processor_data))
+                return counter;
+              counter++;
+            }
+        }
+    }
+
+  return counter;
+}
+
+/* Allocation and clean-up.  */
+
+/* Return a hash index for a NUL-terminated STRING between 0 and N_BUCKETS-1.
+   This is a convenience routine for constructing other hashing functions.  */
+
+#if USE_DIFF_HASH
+
+/* About hashings, Paul Eggert writes to me (FP), on 1994-01-01: "Please see
+   B. J. McKenzie, R. Harries & T. Bell, Selecting a hashing algorithm,
+   Software--practice & experience 20, 2 (Feb 1990), 209-224.  Good hash
+   algorithms tend to be domain-specific, so what's good for [diffutils'] io.c
+   may not be good for your application."  */
+
+size_t
+hash_string (const char *string, size_t n_buckets)
+{
+# define HASH_ONE_CHAR(Value, Byte) \
+  ((Byte) + rotl_sz (Value, 7))
+
+  size_t value = 0;
+  unsigned char ch;
+
+  for (; (ch = *string); string++)
+    value = HASH_ONE_CHAR (value, ch);
+  return value % n_buckets;
+
+# undef HASH_ONE_CHAR
+}
+
+#else /* not USE_DIFF_HASH */
+
+/* This one comes from 'recode', and performs a bit better than the above as
+   per a few experiments.  It is inspired from a hashing routine found in the
+   very old Cyber 'snoop', itself written in typical Greg Mansfield style.
+   (By the way, what happened to this excellent man?  Is he still alive?)  */
+
+size_t
+hash_string (const char *string, size_t n_buckets)
+{
+  size_t value = 0;
+  unsigned char ch;
+
+  for (; (ch = *string); string++)
+    value = (value * 31 + ch) % n_buckets;
+  return value;
+}
+
+#endif /* not USE_DIFF_HASH */
+
+/* Return true if CANDIDATE is a prime number.  CANDIDATE should be an odd
+   number at least equal to 11.  */
+
+static bool _GL_ATTRIBUTE_CONST
+is_prime (size_t candidate)
+{
+  size_t divisor = 3;
+  size_t square = divisor * divisor;
+
+  while (square < candidate && (candidate % divisor))
+    {
+      divisor++;
+      square += 4 * divisor;
+      divisor++;
+    }
+
+  return (candidate % divisor ? true : false);
+}
+
+/* Round a given CANDIDATE number up to the nearest prime, and return that
+   prime.  Primes lower than 10 are merely skipped.  */
+
+static size_t _GL_ATTRIBUTE_CONST
+next_prime (size_t candidate)
+{
+  /* Skip small primes.  */
+  if (candidate < 10)
+    candidate = 10;
+
+  /* Make it definitely odd.  */
+  candidate |= 1;
+
+  while (SIZE_MAX != candidate && !is_prime (candidate))
+    candidate += 2;
+
+  return candidate;
+}
+
+void
+hash_reset_tuning (Hash_tuning *tuning)
+{
+  *tuning = default_tuning;
+}
+
+/* If the user passes a NULL hasher, we hash the raw pointer.  */
+static size_t
+raw_hasher (const void *data, size_t n)
+{
+  /* When hashing unique pointers, it is often the case that they were
+     generated by malloc and thus have the property that the low-order
+     bits are 0.  As this tends to give poorer performance with small
+     tables, we rotate the pointer value before performing division,
+     in an attempt to improve hash quality.  */
+  size_t val = rotr_sz ((size_t) data, 3);
+  return val % n;
+}
+
+/* If the user passes a NULL comparator, we use pointer comparison.  */
+static bool
+raw_comparator (const void *a, const void *b)
+{
+  return a == b;
+}
+
+
+/* For the given hash TABLE, check the user supplied tuning structure for
+   reasonable values, and return true if there is no gross error with it.
+   Otherwise, definitively reset the TUNING field to some acceptable default
+   in the hash table (that is, the user loses the right of further modifying
+   tuning arguments), and return false.  */
+
+static bool
+check_tuning (Hash_table *table)
+{
+  const Hash_tuning *tuning = table->tuning;
+  float epsilon;
+  if (tuning == &default_tuning)
+    return true;
+
+  /* Be a bit stricter than mathematics would require, so that
+     rounding errors in size calculations do not cause allocations to
+     fail to grow or shrink as they should.  The smallest allocation
+     is 11 (due to next_prime's algorithm), so an epsilon of 0.1
+     should be good enough.  */
+  epsilon = 0.1f;
+
+  if (epsilon < tuning->growth_threshold
+      && tuning->growth_threshold < 1 - epsilon
+      && 1 + epsilon < tuning->growth_factor
+      && 0 <= tuning->shrink_threshold
+      && tuning->shrink_threshold + epsilon < tuning->shrink_factor
+      && tuning->shrink_factor <= 1
+      && tuning->shrink_threshold + epsilon < tuning->growth_threshold)
+    return true;
+
+  table->tuning = &default_tuning;
+  return false;
+}
+
+/* Compute the size of the bucket array for the given CANDIDATE and
+   TUNING, or return 0 if there is no possible way to allocate that
+   many entries.  */
+
+static size_t _GL_ATTRIBUTE_PURE
+compute_bucket_size (size_t candidate, const Hash_tuning *tuning)
+{
+  if (!tuning->is_n_buckets)
+    {
+      float new_candidate = candidate / tuning->growth_threshold;
+      if (SIZE_MAX <= new_candidate)
+        return 0;
+      candidate = new_candidate;
+    }
+  candidate = next_prime (candidate);
+  if (xalloc_oversized (candidate, sizeof (struct hash_entry *)))
+    return 0;
+  return candidate;
+}
+
+/* Allocate and return a new hash table, or NULL upon failure.  The initial
+   number of buckets is automatically selected so as to _guarantee_ that you
+   may insert at least CANDIDATE different user entries before any growth of
+   the hash table size occurs.  So, if have a reasonably tight a-priori upper
+   bound on the number of entries you intend to insert in the hash table, you
+   may save some table memory and insertion time, by specifying it here.  If
+   the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
+   argument has its meaning changed to the wanted number of buckets.
+
+   TUNING points to a structure of user-supplied values, in case some fine
+   tuning is wanted over the default behavior of the hasher.  If TUNING is
+   NULL, the default tuning parameters are used instead.  If TUNING is
+   provided but the values requested are out of bounds or might cause
+   rounding errors, return NULL.
+
+   The user-supplied HASHER function, when not NULL, accepts two
+   arguments ENTRY and TABLE_SIZE.  It computes, by hashing ENTRY contents, a
+   slot number for that entry which should be in the range 0..TABLE_SIZE-1.
+   This slot number is then returned.
+
+   The user-supplied COMPARATOR function, when not NULL, accepts two
+   arguments pointing to user data, it then returns true for a pair of entries
+   that compare equal, or false otherwise.  This function is internally called
+   on entries which are already known to hash to the same bucket index,
+   but which are distinct pointers.
+
+   The user-supplied DATA_FREER function, when not NULL, may be later called
+   with the user data as an argument, just before the entry containing the
+   data gets freed.  This happens from within 'hash_free' or 'hash_clear'.
+   You should specify this function only if you want these functions to free
+   all of your 'data' data.  This is typically the case when your data is
+   simply an auxiliary struct that you have malloc'd to aggregate several
+   values.  */
+
+Hash_table *
+hash_initialize (size_t candidate, const Hash_tuning *tuning,
+                 Hash_hasher hasher, Hash_comparator comparator,
+                 Hash_data_freer data_freer)
+{
+  Hash_table *table;
+
+  if (hasher == NULL)
+    hasher = raw_hasher;
+  if (comparator == NULL)
+    comparator = raw_comparator;
+
+  table = malloc (sizeof *table);
+  if (table == NULL)
+    return NULL;
+
+  if (!tuning)
+    tuning = &default_tuning;
+  table->tuning = tuning;
+  if (!check_tuning (table))
+    {
+      /* Fail if the tuning options are invalid.  This is the only occasion
+         when the user gets some feedback about it.  Once the table is created,
+         if the user provides invalid tuning options, we silently revert to
+         using the defaults, and ignore further request to change the tuning
+         options.  */
+      goto fail;
+    }
+
+  table->n_buckets = compute_bucket_size (candidate, tuning);
+  if (!table->n_buckets)
+    goto fail;
+
+  table->bucket = calloc (table->n_buckets, sizeof *table->bucket);
+  if (table->bucket == NULL)
+    goto fail;
+  table->bucket_limit = table->bucket + table->n_buckets;
+  table->n_buckets_used = 0;
+  table->n_entries = 0;
+
+  table->hasher = hasher;
+  table->comparator = comparator;
+  table->data_freer = data_freer;
+
+  table->free_entry_list = NULL;
+#if USE_OBSTACK
+  obstack_init (&table->entry_stack);
+#endif
+  return table;
+
+ fail:
+  free (table);
+  return NULL;
+}
+
+/* Make all buckets empty, placing any chained entries on the free list.
+   Apply the user-specified function data_freer (if any) to the datas of any
+   affected entries.  */
+
+void
+hash_clear (Hash_table *table)
+{
+  struct hash_entry *bucket;
+
+  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+    {
+      if (bucket->data)
+        {
+          struct hash_entry *cursor;
+          struct hash_entry *next;
+
+          /* Free the bucket overflow.  */
+          for (cursor = bucket->next; cursor; cursor = next)
+            {
+              if (table->data_freer)
+                table->data_freer (cursor->data);
+              cursor->data = NULL;
+
+              next = cursor->next;
+              /* Relinking is done one entry at a time, as it is to be expected
+                 that overflows are either rare or short.  */
+              cursor->next = table->free_entry_list;
+              table->free_entry_list = cursor;
+            }
+
+          /* Free the bucket head.  */
+          if (table->data_freer)
+            table->data_freer (bucket->data);
+          bucket->data = NULL;
+          bucket->next = NULL;
+        }
+    }
+
+  table->n_buckets_used = 0;
+  table->n_entries = 0;
+}
+
+/* Reclaim all storage associated with a hash table.  If a data_freer
+   function has been supplied by the user when the hash table was created,
+   this function applies it to the data of each entry before freeing that
+   entry.  */
+
+void
+hash_free (Hash_table *table)
+{
+  struct hash_entry *bucket;
+  struct hash_entry *cursor;
+  struct hash_entry *next;
+
+  /* Call the user data_freer function.  */
+  if (table->data_freer && table->n_entries)
+    {
+      for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+        {
+          if (bucket->data)
+            {
+              for (cursor = bucket; cursor; cursor = cursor->next)
+                table->data_freer (cursor->data);
+            }
+        }
+    }
+
+#if USE_OBSTACK
+
+  obstack_free (&table->entry_stack, NULL);
+
+#else
+
+  /* Free all bucket overflowed entries.  */
+  for (bucket = table->bucket; bucket < table->bucket_limit; bucket++)
+    {
+      for (cursor = bucket->next; cursor; cursor = next)
+        {
+          next = cursor->next;
+          free (cursor);
+        }
+    }
+
+  /* Also reclaim the internal list of previously freed entries.  */
+  for (cursor = table->free_entry_list; cursor; cursor = next)
+    {
+      next = cursor->next;
+      free (cursor);
+    }
+
+#endif
+
+  /* Free the remainder of the hash table structure.  */
+  free (table->bucket);
+  free (table);
+}
+
+/* Insertion and deletion.  */
+
+/* Get a new hash entry for a bucket overflow, possibly by recycling a
+   previously freed one.  If this is not possible, allocate a new one.  */
+
+static struct hash_entry *
+allocate_entry (Hash_table *table)
+{
+  struct hash_entry *new;
+
+  if (table->free_entry_list)
+    {
+      new = table->free_entry_list;
+      table->free_entry_list = new->next;
+    }
+  else
+    {
+#if USE_OBSTACK
+      new = obstack_alloc (&table->entry_stack, sizeof *new);
+#else
+      new = malloc (sizeof *new);
+#endif
+    }
+
+  return new;
+}
+
+/* Free a hash entry which was part of some bucket overflow,
+   saving it for later recycling.  */
+
+static void
+free_entry (Hash_table *table, struct hash_entry *entry)
+{
+  entry->data = NULL;
+  entry->next = table->free_entry_list;
+  table->free_entry_list = entry;
+}
+
+/* This private function is used to help with insertion and deletion.  When
+   ENTRY matches an entry in the table, return a pointer to the corresponding
+   user data and set *BUCKET_HEAD to the head of the selected bucket.
+   Otherwise, return NULL.  When DELETE is true and ENTRY matches an entry in
+   the table, unlink the matching entry.  */
+
+static void *
+hash_find_entry (Hash_table *table, const void *entry,
+                 struct hash_entry **bucket_head, bool delete)
+{
+  struct hash_entry *bucket = safe_hasher (table, entry);
+  struct hash_entry *cursor;
+
+  *bucket_head = bucket;
+
+  /* Test for empty bucket.  */
+  if (bucket->data == NULL)
+    return NULL;
+
+  /* See if the entry is the first in the bucket.  */
+  if (entry == bucket->data || table->comparator (entry, bucket->data))
+    {
+      void *data = bucket->data;
+
+      if (delete)
+        {
+          if (bucket->next)
+            {
+              struct hash_entry *next = bucket->next;
+
+              /* Bump the first overflow entry into the bucket head, then save
+                 the previous first overflow entry for later recycling.  */
+              *bucket = *next;
+              free_entry (table, next);
+            }
+          else
+            {
+              bucket->data = NULL;
+            }
+        }
+
+      return data;
+    }
+
+  /* Scan the bucket overflow.  */
+  for (cursor = bucket; cursor->next; cursor = cursor->next)
+    {
+      if (entry == cursor->next->data
+          || table->comparator (entry, cursor->next->data))
+        {
+          void *data = cursor->next->data;
+
+          if (delete)
+            {
+              struct hash_entry *next = cursor->next;
+
+              /* Unlink the entry to delete, then save the freed entry for later
+                 recycling.  */
+              cursor->next = next->next;
+              free_entry (table, next);
+            }
+
+          return data;
+        }
+    }
+
+  /* No entry found.  */
+  return NULL;
+}
+
+/* Internal helper, to move entries from SRC to DST.  Both tables must
+   share the same free entry list.  If SAFE, only move overflow
+   entries, saving bucket heads for later, so that no allocations will
+   occur.  Return false if the free entry list is exhausted and an
+   allocation fails.  */
+
+static bool
+transfer_entries (Hash_table *dst, Hash_table *src, bool safe)
+{
+  struct hash_entry *bucket;
+  struct hash_entry *cursor;
+  struct hash_entry *next;
+  for (bucket = src->bucket; bucket < src->bucket_limit; bucket++)
+    if (bucket->data)
+      {
+        void *data;
+        struct hash_entry *new_bucket;
+
+        /* Within each bucket, transfer overflow entries first and
+           then the bucket head, to minimize memory pressure.  After
+           all, the only time we might allocate is when moving the
+           bucket head, but moving overflow entries first may create
+           free entries that can be recycled by the time we finally
+           get to the bucket head.  */
+        for (cursor = bucket->next; cursor; cursor = next)
+          {
+            data = cursor->data;
+            new_bucket = safe_hasher (dst, data);
+
+            next = cursor->next;
+
+            if (new_bucket->data)
+              {
+                /* Merely relink an existing entry, when moving from a
+                   bucket overflow into a bucket overflow.  */
+                cursor->next = new_bucket->next;
+                new_bucket->next = cursor;
+              }
+            else
+              {
+                /* Free an existing entry, when moving from a bucket
+                   overflow into a bucket header.  */
+                new_bucket->data = data;
+                dst->n_buckets_used++;
+                free_entry (dst, cursor);
+              }
+          }
+        /* Now move the bucket head.  Be sure that if we fail due to
+           allocation failure that the src table is in a consistent
+           state.  */
+        data = bucket->data;
+        bucket->next = NULL;
+        if (safe)
+          continue;
+        new_bucket = safe_hasher (dst, data);
+
+        if (new_bucket->data)
+          {
+            /* Allocate or recycle an entry, when moving from a bucket
+               header into a bucket overflow.  */
+            struct hash_entry *new_entry = allocate_entry (dst);
+
+            if (new_entry == NULL)
+              return false;
+
+            new_entry->data = data;
+            new_entry->next = new_bucket->next;
+            new_bucket->next = new_entry;
+          }
+        else
+          {
+            /* Move from one bucket header to another.  */
+            new_bucket->data = data;
+            dst->n_buckets_used++;
+          }
+        bucket->data = NULL;
+        src->n_buckets_used--;
+      }
+  return true;
+}
+
+/* For an already existing hash table, change the number of buckets through
+   specifying CANDIDATE.  The contents of the hash table are preserved.  The
+   new number of buckets is automatically selected so as to _guarantee_ that
+   the table may receive at least CANDIDATE different user entries, including
+   those already in the table, before any other growth of the hash table size
+   occurs.  If TUNING->IS_N_BUCKETS is true, then CANDIDATE specifies the
+   exact number of buckets desired.  Return true iff the rehash succeeded.  */
+
+bool
+hash_rehash (Hash_table *table, size_t candidate)
+{
+  Hash_table storage;
+  Hash_table *new_table;
+  size_t new_size = compute_bucket_size (candidate, table->tuning);
+
+  if (!new_size)
+    return false;
+  if (new_size == table->n_buckets)
+    return true;
+  new_table = &storage;
+  new_table->bucket = calloc (new_size, sizeof *new_table->bucket);
+  if (new_table->bucket == NULL)
+    return false;
+  new_table->n_buckets = new_size;
+  new_table->bucket_limit = new_table->bucket + new_size;
+  new_table->n_buckets_used = 0;
+  new_table->n_entries = 0;
+  new_table->tuning = table->tuning;
+  new_table->hasher = table->hasher;
+  new_table->comparator = table->comparator;
+  new_table->data_freer = table->data_freer;
+
+  /* In order for the transfer to successfully complete, we need
+     additional overflow entries when distinct buckets in the old
+     table collide into a common bucket in the new table.  The worst
+     case possible is a hasher that gives a good spread with the old
+     size, but returns a constant with the new size; if we were to
+     guarantee table->n_buckets_used-1 free entries in advance, then
+     the transfer would be guaranteed to not allocate memory.
+     However, for large tables, a guarantee of no further allocation
+     introduces a lot of extra memory pressure, all for an unlikely
+     corner case (most rehashes reduce, rather than increase, the
+     number of overflow entries needed).  So, we instead ensure that
+     the transfer process can be reversed if we hit a memory
+     allocation failure mid-transfer.  */
+
+  /* Merely reuse the extra old space into the new table.  */
+#if USE_OBSTACK
+  new_table->entry_stack = table->entry_stack;
+#endif
+  new_table->free_entry_list = table->free_entry_list;
+
+  if (transfer_entries (new_table, table, false))
+    {
+      /* Entries transferred successfully; tie up the loose ends.  */
+      free (table->bucket);
+      table->bucket = new_table->bucket;
+      table->bucket_limit = new_table->bucket_limit;
+      table->n_buckets = new_table->n_buckets;
+      table->n_buckets_used = new_table->n_buckets_used;
+      table->free_entry_list = new_table->free_entry_list;
+      /* table->n_entries and table->entry_stack already hold their value.  */
+      return true;
+    }
+
+  /* We've allocated new_table->bucket (and possibly some entries),
+     exhausted the free list, and moved some but not all entries into
+     new_table.  We must undo the partial move before returning
+     failure.  The only way to get into this situation is if new_table
+     uses fewer buckets than the old table, so we will reclaim some
+     free entries as overflows in the new table are put back into
+     distinct buckets in the old table.
+
+     There are some pathological cases where a single pass through the
+     table requires more intermediate overflow entries than using two
+     passes.  Two passes give worse cache performance and takes
+     longer, but at this point, we're already out of memory, so slow
+     and safe is better than failure.  */
+  table->free_entry_list = new_table->free_entry_list;
+  if (! (transfer_entries (table, new_table, true)
+         && transfer_entries (table, new_table, false)))
+    abort ();
+  /* table->n_entries already holds its value.  */
+  free (new_table->bucket);
+  return false;
+}
+
+/* Insert ENTRY into hash TABLE if there is not already a matching entry.
+
+   Return -1 upon memory allocation failure.
+   Return 1 if insertion succeeded.
+   Return 0 if there is already a matching entry in the table,
+   and in that case, if MATCHED_ENT is non-NULL, set *MATCHED_ENT
+   to that entry.
+
+   This interface is easier to use than hash_insert when you must
+   distinguish between the latter two cases.  More importantly,
+   hash_insert is unusable for some types of ENTRY values.  When using
+   hash_insert, the only way to distinguish those cases is to compare
+   the return value and ENTRY.  That works only when you can have two
+   different ENTRY values that point to data that compares "equal".  Thus,
+   when the ENTRY value is a simple scalar, you must use
+   hash_insert_if_absent.  ENTRY must not be NULL.  */
+int
+hash_insert_if_absent (Hash_table *table, void const *entry,
+                       void const **matched_ent)
+{
+  void *data;
+  struct hash_entry *bucket;
+
+  /* The caller cannot insert a NULL entry, since hash_lookup returns NULL
+     to indicate "not found", and hash_find_entry uses "bucket->data == NULL"
+     to indicate an empty bucket.  */
+  if (! entry)
+    abort ();
+
+  /* If there's a matching entry already in the table, return that.  */
+  if ((data = hash_find_entry (table, entry, &bucket, false)) != NULL)
+    {
+      if (matched_ent)
+        *matched_ent = data;
+      return 0;
+    }
+
+  /* If the growth threshold of the buckets in use has been reached, increase
+     the table size and rehash.  There's no point in checking the number of
+     entries:  if the hashing function is ill-conditioned, rehashing is not
+     likely to improve it.  */
+
+  if (table->n_buckets_used
+      > table->tuning->growth_threshold * table->n_buckets)
+    {
+      /* Check more fully, before starting real work.  If tuning arguments
+         became invalid, the second check will rely on proper defaults.  */
+      check_tuning (table);
+      if (table->n_buckets_used
+          > table->tuning->growth_threshold * table->n_buckets)
+        {
+          const Hash_tuning *tuning = table->tuning;
+          float candidate =
+            (tuning->is_n_buckets
+             ? (table->n_buckets * tuning->growth_factor)
+             : (table->n_buckets * tuning->growth_factor
+                * tuning->growth_threshold));
+
+          if (SIZE_MAX <= candidate)
+            return -1;
+
+          /* If the rehash fails, arrange to return NULL.  */
+          if (!hash_rehash (table, candidate))
+            return -1;
+
+          /* Update the bucket we are interested in.  */
+          if (hash_find_entry (table, entry, &bucket, false) != NULL)
+            abort ();
+        }
+    }
+
+  /* ENTRY is not matched, it should be inserted.  */
+
+  if (bucket->data)
+    {
+      struct hash_entry *new_entry = allocate_entry (table);
+
+      if (new_entry == NULL)
+        return -1;
+
+      /* Add ENTRY in the overflow of the bucket.  */
+
+      new_entry->data = (void *) entry;
+      new_entry->next = bucket->next;
+      bucket->next = new_entry;
+      table->n_entries++;
+      return 1;
+    }
+
+  /* Add ENTRY right in the bucket head.  */
+
+  bucket->data = (void *) entry;
+  table->n_entries++;
+  table->n_buckets_used++;
+
+  return 1;
+}
+
+/* If ENTRY matches an entry already in the hash table, return the pointer
+   to the entry from the table.  Otherwise, insert ENTRY and return ENTRY.
+   Return NULL if the storage required for insertion cannot be allocated.
+   This implementation does not support duplicate entries or insertion of
+   NULL.  */
+
+void *
+hash_insert (Hash_table *table, void const *entry)
+{
+  void const *matched_ent;
+  int err = hash_insert_if_absent (table, entry, &matched_ent);
+  return (err == -1
+          ? NULL
+          : (void *) (err == 0 ? matched_ent : entry));
+}
+
+/* If ENTRY is already in the table, remove it and return the just-deleted
+   data (the user may want to deallocate its storage).  If ENTRY is not in the
+   table, don't modify the table and return NULL.  */
+
+void *
+hash_delete (Hash_table *table, const void *entry)
+{
+  void *data;
+  struct hash_entry *bucket;
+
+  data = hash_find_entry (table, entry, &bucket, true);
+  if (!data)
+    return NULL;
+
+  table->n_entries--;
+  if (!bucket->data)
+    {
+      table->n_buckets_used--;
+
+      /* If the shrink threshold of the buckets in use has been reached,
+         rehash into a smaller table.  */
+
+      if (table->n_buckets_used
+          < table->tuning->shrink_threshold * table->n_buckets)
+        {
+          /* Check more fully, before starting real work.  If tuning arguments
+             became invalid, the second check will rely on proper defaults.  */
+          check_tuning (table);
+          if (table->n_buckets_used
+              < table->tuning->shrink_threshold * table->n_buckets)
+            {
+              const Hash_tuning *tuning = table->tuning;
+              size_t candidate =
+                (tuning->is_n_buckets
+                 ? table->n_buckets * tuning->shrink_factor
+                 : (table->n_buckets * tuning->shrink_factor
+                    * tuning->growth_threshold));
+
+              if (!hash_rehash (table, candidate))
+                {
+                  /* Failure to allocate memory in an attempt to
+                     shrink the table is not fatal.  But since memory
+                     is low, we can at least be kind and free any
+                     spare entries, rather than keeping them tied up
+                     in the free entry list.  */
+#if ! USE_OBSTACK
+                  struct hash_entry *cursor = table->free_entry_list;
+                  struct hash_entry *next;
+                  while (cursor)
+                    {
+                      next = cursor->next;
+                      free (cursor);
+                      cursor = next;
+                    }
+                  table->free_entry_list = NULL;
+#endif
+                }
+            }
+        }
+    }
+
+  return data;
+}
+
+/* Testing.  */
+
+#if TESTING
+
+void
+hash_print (const Hash_table *table)
+{
+  struct hash_entry *bucket = (struct hash_entry *) table->bucket;
+
+  for ( ; bucket < table->bucket_limit; bucket++)
+    {
+      struct hash_entry *cursor;
+
+      if (bucket)
+        printf ("%lu:\n", (unsigned long int) (bucket - table->bucket));
+
+      for (cursor = bucket; cursor; cursor = cursor->next)
+        {
+          char const *s = cursor->data;
+          /* FIXME */
+          if (s)
+            printf ("  %s\n", s);
+        }
+    }
+}
+
+#endif /* TESTING */