/* 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 Lesser General Public License as published by

   the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser 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);