dbus-hash.c 60.1 KB
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/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
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/* dbus-hash.c Generic hash table utility (internal to D-Bus implementation)
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 * 
 * Copyright (C) 2002  Red Hat, Inc.
 * Copyright (c) 1991-1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 * 
 * Hash table implementation based on generic/tclHash.c from the Tcl
 * source code. The original Tcl license applies to portions of the
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 * code from tclHash.c; the Tcl license follows this standad D-Bus 
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 * license information.
 *
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 * Licensed under the Academic Free License version 2.1
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 * 
 * 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 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, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
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 *
 */
/* 
 * The following copyright applies to code from the Tcl distribution.
 *
 * Copyright (c) 1991-1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * This software is copyrighted by the Regents of the University of
 * California, Sun Microsystems, Inc., Scriptics Corporation, and
 * other parties.  The following terms apply to all files associated
 * with the software unless explicitly disclaimed in individual files.
 * 
 * The authors hereby grant permission to use, copy, modify,
 * distribute, and license this software and its documentation for any
 * purpose, provided that existing copyright notices are retained in
 * all copies and that this notice is included verbatim in any
 * distributions. No written agreement, license, or royalty fee is
 * required for any of the authorized uses.  Modifications to this
 * software may be copyrighted by their authors and need not follow
 * the licensing terms described here, provided that the new terms are
 * clearly indicated on the first page of each file where they apply.
 * 
 * IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY
 * PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
 * DAMAGES ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION,
 * OR ANY DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 * THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND
 * NON-INFRINGEMENT.  THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS,
 * AND THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
 * MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 * 
 * GOVERNMENT USE: If you are acquiring this software on behalf of the
 * U.S. government, the Government shall have only "Restricted Rights"
 * in the software and related documentation as defined in the Federal
 * Acquisition Regulations (FARs) in Clause 52.227.19 (c) (2).  If you
 * are acquiring the software on behalf of the Department of Defense,
 * the software shall be classified as "Commercial Computer Software"
 * and the Government shall have only "Restricted Rights" as defined
 * in Clause 252.227-7013 (c) (1) of DFARs.  Notwithstanding the
 * foregoing, the authors grant the U.S. Government and others acting
 * in its behalf permission to use and distribute the software in
 * accordance with the terms specified in this license.
 */

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#include <config.h>
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#include "dbus-hash.h"
#include "dbus-internals.h"
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#include "dbus-mempool.h"
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/**
 * @defgroup DBusHashTable Hash table
 * @ingroup  DBusInternals
 * @brief DBusHashTable data structure
 *
 * Types and functions related to DBusHashTable.
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 */

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/**
 * @defgroup DBusHashTableInternals Hash table implementation details
 * @ingroup  DBusInternals
 * @brief DBusHashTable implementation details
 *
 * The guts of DBusHashTable.
 *
 * @{
 */
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/**
 * When there are this many entries per bucket, on average, rebuild
 * the hash table to make it larger.
 */
#define REBUILD_MULTIPLIER  3

/**
 * Takes a preliminary integer hash value and produces an index into a
 * hash tables bucket list.  The idea is to make it so that
 * preliminary values that are arbitrarily similar will end up in
 * different buckets.  The hash function was taken from a
 * random-number generator. (This is used to hash integers.)
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 *
 * The down_shift drops off the high bits of the hash index, and
 * decreases as we increase the number of hash buckets (to keep more
 * range in the hash index). The mask also strips high bits and strips
 * fewer high bits as the number of hash buckets increases.
 * I don't understand two things: why is the initial downshift 28
 * to keep 4 bits when the initial mask is 011 to keep 2 bits,
 * and why do we have both a mask and a downshift?
 * 
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 */
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#define RANDOM_INDEX(table, i) \
    (((((long) (i))*1103515245) >> (table)->down_shift) & (table)->mask)
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/**
 * Initial number of buckets in hash table (hash table statically
 * allocates its buckets for this size and below).
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 * The initial mask has to be synced to this.
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 */
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#define DBUS_SMALL_HASH_TABLE 4
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/**
 * Typedef for DBusHashEntry
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 */
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typedef struct DBusHashEntry DBusHashEntry;
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/**
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 * @brief Internal representation of a hash entry.
 * 
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 * A single entry (key-value pair) in the hash table.
 * Internal to hash table implementation.
 */
struct DBusHashEntry
{
  DBusHashEntry *next;    /**< Pointer to next entry in this
                           * hash bucket, or #NULL for end of
                           * chain.
                           */
  void *key;              /**< Hash key */
  void *value;            /**< Hash value */
};

/**
 * Function used to find and optionally create a hash entry.
 */
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typedef DBusHashEntry* (* DBusFindEntryFunction) (DBusHashTable        *table,
                                                  void                 *key,
                                                  dbus_bool_t           create_if_not_found,
                                                  DBusHashEntry      ***bucket,
                                                  DBusPreallocatedHash *preallocated);
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/**
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 * @brief Internals of DBusHashTable.
 * 
 * Hash table internals. Hash tables are opaque objects, they must be
 * used via accessor functions.
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 */
struct DBusHashTable {
  int refcount;                       /**< Reference count */
  
  DBusHashEntry **buckets;            /**< Pointer to bucket array.  Each
                                       * element points to first entry in
                                       * bucket's hash chain, or #NULL.
                                       */
  DBusHashEntry *static_buckets[DBUS_SMALL_HASH_TABLE];
                                       /**< Bucket array used for small tables
                                        * (to avoid mallocs and frees).
                                        */
  int n_buckets;                       /**< Total number of buckets allocated
                                        * at **buckets.
                                        */
  int n_entries;                       /**< Total number of entries present
                                        * in table.
                                        */
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  int hi_rebuild_size;                 /**< Enlarge table when n_entries gets
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                                        * to be this large.
                                        */
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  int lo_rebuild_size;                 /**< Shrink table when n_entries gets
                                        * below this.
                                        */
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  int down_shift;                      /**< Shift count used in hashing
                                        * function.  Designed to use high-
                                        * order bits of randomized keys.
                                        */
  int mask;                            /**< Mask value used in hashing
                                        * function.
                                        */
  DBusHashType key_type;               /**< Type of keys used in this table */


  DBusFindEntryFunction find_function; /**< Function for finding entries */

  DBusFreeFunction free_key_function;   /**< Function to free keys */
  DBusFreeFunction free_value_function; /**< Function to free values */
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  DBusMemPool *entry_pool;              /**< Memory pool for hash entries */
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};

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/** 
 * @brief Internals of DBusHashIter.
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 */
typedef struct
{
  DBusHashTable *table;     /**< Pointer to table containing entry. */
  DBusHashEntry **bucket;   /**< Pointer to bucket that points to
                             * first entry in this entry's chain:
                             * used for deleting the entry.
                             */
  DBusHashEntry *entry;      /**< Current hash entry */
  DBusHashEntry *next_entry; /**< Next entry to be iterated onto in current bucket */
  int next_bucket;           /**< index of next bucket */
  int n_entries_on_init;     /**< used to detect table resize since initialization */
} DBusRealHashIter;

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static DBusHashEntry* find_direct_function      (DBusHashTable          *table,
                                                 void                   *key,
                                                 dbus_bool_t             create_if_not_found,
                                                 DBusHashEntry        ***bucket,
                                                 DBusPreallocatedHash   *preallocated);
static DBusHashEntry* find_string_function      (DBusHashTable          *table,
                                                 void                   *key,
                                                 dbus_bool_t             create_if_not_found,
                                                 DBusHashEntry        ***bucket,
                                                 DBusPreallocatedHash   *preallocated);
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#ifdef DBUS_BUILD_TESTS
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static DBusHashEntry* find_two_strings_function (DBusHashTable          *table,
                                                 void                   *key,
                                                 dbus_bool_t             create_if_not_found,
                                                 DBusHashEntry        ***bucket,
                                                 DBusPreallocatedHash   *preallocated);
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#endif
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static unsigned int   string_hash               (const char             *str);
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#ifdef DBUS_BUILD_TESTS
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static unsigned int   two_strings_hash          (const char             *str);
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#endif
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static void           rebuild_table             (DBusHashTable          *table);
static DBusHashEntry* alloc_entry               (DBusHashTable          *table);
static void           remove_entry              (DBusHashTable          *table,
                                                 DBusHashEntry         **bucket,
                                                 DBusHashEntry          *entry);
static void           free_entry                (DBusHashTable          *table,
                                                 DBusHashEntry          *entry);
static void           free_entry_data           (DBusHashTable          *table,
                                                 DBusHashEntry          *entry);
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/** @} */
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/**
 * @addtogroup DBusHashTable
 * @{
 */
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/**
 * @typedef DBusHashIter
 *
 * Public opaque hash table iterator object.
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 */

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/**
 * @typedef DBusHashTable
 *
 * Public opaque hash table object.
 */
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/**
 * @typedef DBusHashType
 *
 * Indicates the type of a key in the hash table.
 */
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/**
 * Constructs a new hash table. Should be freed with
 * _dbus_hash_table_unref(). If memory cannot be
 * allocated for the hash table, returns #NULL.
 *
 * @param type the type of hash key to use.
 * @param key_free_function function to free hash keys.
 * @param value_free_function function to free hash values.
 * @returns a new DBusHashTable or #NULL if no memory.
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 */
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DBusHashTable*
_dbus_hash_table_new (DBusHashType     type,
                      DBusFreeFunction key_free_function,
                      DBusFreeFunction value_free_function)
{
  DBusHashTable *table;
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  DBusMemPool *entry_pool;
  
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  table = dbus_new0 (DBusHashTable, 1);
  if (table == NULL)
    return NULL;
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  entry_pool = _dbus_mem_pool_new (sizeof (DBusHashEntry), TRUE);
  if (entry_pool == NULL)
    {
      dbus_free (table);
      return NULL;
    }
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  table->refcount = 1;
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  table->entry_pool = entry_pool;
  
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  _dbus_assert (DBUS_SMALL_HASH_TABLE == _DBUS_N_ELEMENTS (table->static_buckets));
  
  table->buckets = table->static_buckets;  
  table->n_buckets = DBUS_SMALL_HASH_TABLE;
  table->n_entries = 0;
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  table->hi_rebuild_size = DBUS_SMALL_HASH_TABLE * REBUILD_MULTIPLIER;
  table->lo_rebuild_size = 0;
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  table->down_shift = 28;
  table->mask = 3;
  table->key_type = type;
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  _dbus_assert (table->mask < table->n_buckets);
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  switch (table->key_type)
    {
    case DBUS_HASH_INT:
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    case DBUS_HASH_POINTER:
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    case DBUS_HASH_ULONG:
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      table->find_function = find_direct_function;
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      break;
    case DBUS_HASH_STRING:
      table->find_function = find_string_function;
      break;
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    case DBUS_HASH_TWO_STRINGS:
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#ifdef DBUS_BUILD_TESTS
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      table->find_function = find_two_strings_function;
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#endif
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      break;
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    default:
      _dbus_assert_not_reached ("Unknown hash table type");
      break;
    }
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  table->free_key_function = key_free_function;
  table->free_value_function = value_free_function;
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  return table;
}
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/**
 * Increments the reference count for a hash table.
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 *
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 * @param table the hash table to add a reference to.
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 * @returns the hash table.
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 */
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DBusHashTable *
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_dbus_hash_table_ref (DBusHashTable *table)
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{
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  table->refcount += 1;
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  return table;
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}
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/**
 * Decrements the reference count for a hash table,
 * freeing the hash table if the count reaches zero.
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 *
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 * @param table the hash table to remove a reference from.
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 */
void
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_dbus_hash_table_unref (DBusHashTable *table)
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{
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  table->refcount -= 1;

  if (table->refcount == 0)
    {
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#if 0
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      DBusHashEntry *entry;
      DBusHashEntry *next;
      int i;

      /* Free the entries in the table. */
      for (i = 0; i < table->n_buckets; i++)
        {
          entry = table->buckets[i];
          while (entry != NULL)
            {
              next = entry->next;

              free_entry (table, entry);
              
              entry = next;
            }
        }
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#else
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      DBusHashEntry *entry;
      int i;

      /* Free the entries in the table. */
      for (i = 0; i < table->n_buckets; i++)
        {
          entry = table->buckets[i];
          while (entry != NULL)
            {
              free_entry_data (table, entry);
              
              entry = entry->next;
            }
        }
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      /* We can do this very quickly with memory pools ;-) */
      _dbus_mem_pool_free (table->entry_pool);
#endif
      
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      /* Free the bucket array, if it was dynamically allocated. */
      if (table->buckets != table->static_buckets)
        dbus_free (table->buckets);

      dbus_free (table);
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    }
}
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/**
 * Removed all entries from a hash table.
 *
 * @param table the hash table to remove all entries from.
 */
void
_dbus_hash_table_remove_all (DBusHashTable *table)
{
  DBusHashIter iter;
  _dbus_hash_iter_init (table, &iter);
  while (_dbus_hash_iter_next (&iter))
    {
      _dbus_hash_iter_remove_entry(&iter);
    }
}

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static DBusHashEntry*
alloc_entry (DBusHashTable *table)
{
  DBusHashEntry *entry;

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  entry = _dbus_mem_pool_alloc (table->entry_pool);
  
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  return entry;
}

static void
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free_entry_data (DBusHashTable  *table,
		 DBusHashEntry  *entry)
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{
  if (table->free_key_function)
    (* table->free_key_function) (entry->key);
  if (table->free_value_function)
    (* table->free_value_function) (entry->value);
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}

static void
free_entry (DBusHashTable  *table,
            DBusHashEntry  *entry)
{
  free_entry_data (table, entry);
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  _dbus_mem_pool_dealloc (table->entry_pool, entry);
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}

static void
remove_entry (DBusHashTable  *table,
              DBusHashEntry **bucket,
              DBusHashEntry  *entry)
{
  _dbus_assert (table != NULL);
  _dbus_assert (bucket != NULL);
  _dbus_assert (*bucket != NULL);  
  _dbus_assert (entry != NULL);
  
  if (*bucket == entry)
    *bucket = entry->next;
  else
    {
      DBusHashEntry *prev;
      prev = *bucket;

      while (prev->next != entry)
        prev = prev->next;      
      
      _dbus_assert (prev != NULL);

      prev->next = entry->next;
    }
  
  table->n_entries -= 1;
  free_entry (table, entry);
}

/**
 * Initializes a hash table iterator. To iterate over all entries in a
 * hash table, use the following code (the printf assumes a hash
 * from strings to strings obviously):
 *
 * @code
 * DBusHashIter iter;
 *
 * _dbus_hash_iter_init (table, &iter);
 * while (_dbus_hash_iter_next (&iter))
 *   {
 *      printf ("The first key is %s and value is %s\n",
 *              _dbus_hash_iter_get_string_key (&iter),
 *              _dbus_hash_iter_get_value (&iter));
 *   }
 * 
 * 
 * @endcode
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 *
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 * The iterator is initialized pointing "one before" the first hash
 * entry. The first call to _dbus_hash_iter_next() moves it onto
 * the first valid entry or returns #FALSE if the hash table is
 * empty. Subsequent calls move to the next valid entry or return
 * #FALSE if there are no more entries.
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 *
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 * Note that it is guaranteed to be safe to remove a hash entry during
 * iteration, but it is not safe to add a hash entry.
 * 
 * @param table the hash table to iterate over.
 * @param iter the iterator to initialize.
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 */
void
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_dbus_hash_iter_init (DBusHashTable *table,
                      DBusHashIter  *iter)
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{
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  DBusRealHashIter *real;
  
  _dbus_assert (sizeof (DBusHashIter) == sizeof (DBusRealHashIter));
  
  real = (DBusRealHashIter*) iter;

  real->table = table;
  real->bucket = NULL;
  real->entry = NULL;
  real->next_entry = NULL;
  real->next_bucket = 0;
  real->n_entries_on_init = table->n_entries;
}
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/**
 * Move the hash iterator forward one step, to the next hash entry.
 * The documentation for _dbus_hash_iter_init() explains in more
 * detail.
 *
 * @param iter the iterator to move forward.
 * @returns #FALSE if there are no more entries to move to.
 */
dbus_bool_t
_dbus_hash_iter_next (DBusHashIter  *iter)
{
  DBusRealHashIter *real;
  
  _dbus_assert (sizeof (DBusHashIter) == sizeof (DBusRealHashIter));
  
  real = (DBusRealHashIter*) iter;

  /* if this assertion failed someone probably added hash entries
   * during iteration, which is bad.
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   */
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  _dbus_assert (real->n_entries_on_init >= real->table->n_entries);
  
  /* Remember that real->entry may have been deleted */
  
  while (real->next_entry == NULL)
    {
      if (real->next_bucket >= real->table->n_buckets)
        {
          /* invalidate iter and return false */
          real->entry = NULL;
          real->table = NULL;
          real->bucket = NULL;
          return FALSE;
        }
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      real->bucket = &(real->table->buckets[real->next_bucket]);
      real->next_entry = *(real->bucket);
      real->next_bucket += 1;
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    }

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  _dbus_assert (real->next_entry != NULL);
  _dbus_assert (real->bucket != NULL);
  
  real->entry = real->next_entry;
  real->next_entry = real->entry->next;
  
  return TRUE;
}
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/**
 * Removes the current entry from the hash table.
 * If a key_free_function or value_free_function
 * was provided to _dbus_hash_table_new(),
 * frees the key and/or value for this entry.
 *
 * @param iter the hash table iterator.
 */
void
_dbus_hash_iter_remove_entry (DBusHashIter *iter)
{
  DBusRealHashIter *real;
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  real = (DBusRealHashIter*) iter;
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  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);
  _dbus_assert (real->bucket != NULL);
  
  remove_entry (real->table, real->bucket, real->entry);

  real->entry = NULL; /* make it crash if you try to use this entry */
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}
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/**
 * Gets the value of the current entry.
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 *
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 * @param iter the hash table iterator.
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 */
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void*
_dbus_hash_iter_get_value (DBusHashIter *iter)
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{
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  DBusRealHashIter *real;

  real = (DBusRealHashIter*) iter;

  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);

  return real->entry->value;
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}
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/**
 * Sets the value of the current entry.
 * If the hash table has a value_free_function
 * it will be used to free the previous value.
 * The hash table will own the passed-in value
 * (it will not be copied).
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 *
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 * @param iter the hash table iterator.
 * @param value the new value.
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 */
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void
_dbus_hash_iter_set_value (DBusHashIter *iter,
                           void         *value)
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{
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  DBusRealHashIter *real;
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  real = (DBusRealHashIter*) iter;

  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);

  if (real->table->free_value_function && value != real->entry->value)    
    (* real->table->free_value_function) (real->entry->value);
  
  real->entry->value = value;
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}
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/**
 * Gets the key for the current entry.
 * Only works for hash tables of type #DBUS_HASH_INT.
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 *
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 * @param iter the hash table iterator.
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 */
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int
_dbus_hash_iter_get_int_key (DBusHashIter *iter)
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{
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  DBusRealHashIter *real;
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  real = (DBusRealHashIter*) iter;
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  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);
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  return _DBUS_POINTER_TO_INT (real->entry->key);
}
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/**
 * Gets the key for the current entry.
 * Only works for hash tables of type #DBUS_HASH_ULONG.
 *
 * @param iter the hash table iterator.
 */
unsigned long
_dbus_hash_iter_get_ulong_key (DBusHashIter *iter)
{
  DBusRealHashIter *real;

  real = (DBusRealHashIter*) iter;

  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);

  return (unsigned long) real->entry->key;
}

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/**
 * Gets the key for the current entry.
 * Only works for hash tables of type #DBUS_HASH_STRING
 * @param iter the hash table iterator.
 */
const char*
_dbus_hash_iter_get_string_key (DBusHashIter *iter)
{
  DBusRealHashIter *real;

  real = (DBusRealHashIter*) iter;

  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);

  return real->entry->key;
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}
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#ifdef DBUS_BUILD_TESTS
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/**
 * Gets the key for the current entry.
 * Only works for hash tables of type #DBUS_HASH_TWO_STRINGS
 * @param iter the hash table iterator.
 */
const char*
_dbus_hash_iter_get_two_strings_key (DBusHashIter *iter)
{
  DBusRealHashIter *real;

  real = (DBusRealHashIter*) iter;

  _dbus_assert (real->table != NULL);
  _dbus_assert (real->entry != NULL);

  return real->entry->key;
}
740
#endif /* DBUS_BUILD_TESTS */
741

742 743 744 745 746
/**
 * A low-level but efficient interface for manipulating the hash
 * table.  It's efficient because you can get, set, and optionally
 * create the hash entry while only running the hash function one
 * time.
747
 *
748 749 750 751 752
 * Note that while calling _dbus_hash_iter_next() on the iterator
 * filled in by this function may work, it's completely
 * undefined which entries are after this iter and which
 * are before it. So it would be silly to iterate using this
 * iterator.
753
 *
754 755
 * If the hash entry is created, its value will be initialized
 * to all bits zero.
756
 *
757 758 759
 * #FALSE may be returned due to memory allocation failure, or
 * because create_if_not_found was #FALSE and the entry
 * did not exist.
760
 *
761 762 763
 * If create_if_not_found is #TRUE and the entry is created, the hash
 * table takes ownership of the key that's passed in.
 *
764 765 766 767 768 769 770 771
 * For a hash table of type #DBUS_HASH_INT, cast the int
 * key to the key parameter using #_DBUS_INT_TO_POINTER().
 * 
 * @param table the hash table.
 * @param key the hash key.
 * @param create_if_not_found if #TRUE, create the entry if it didn't exist.
 * @param iter the iterator to initialize.
 * @returns #TRUE if the hash entry now exists (and the iterator is thus valid).
772
 */
773 774 775 776 777 778 779 780 781 782 783 784 785 786
dbus_bool_t
_dbus_hash_iter_lookup (DBusHashTable *table,
                        void          *key,
                        dbus_bool_t    create_if_not_found,
                        DBusHashIter  *iter)
{
  DBusRealHashIter *real;
  DBusHashEntry *entry;
  DBusHashEntry **bucket;
  
  _dbus_assert (sizeof (DBusHashIter) == sizeof (DBusRealHashIter));
  
  real = (DBusRealHashIter*) iter;

787
  entry = (* table->find_function) (table, key, create_if_not_found, &bucket, NULL);
788 789 790 791 792 793 794 795 796 797 798 799 800 801 802

  if (entry == NULL)
    return FALSE;
  
  real->table = table;
  real->bucket = bucket;
  real->entry = entry;
  real->next_entry = entry->next;
  real->next_bucket = (bucket - table->buckets) + 1;
  real->n_entries_on_init = table->n_entries; 

  _dbus_assert (&(table->buckets[real->next_bucket-1]) == real->bucket);
  
  return TRUE;
}
803

804 805 806 807 808 809
static void
add_allocated_entry (DBusHashTable   *table,
                     DBusHashEntry   *entry,
                     unsigned int     idx,
                     void            *key,
                     DBusHashEntry ***bucket)
810
{
811
  DBusHashEntry **b;  
812 813 814 815 816 817 818 819 820 821 822
  
  entry->key = key;
  
  b = &(table->buckets[idx]);
  entry->next = *b;
  *b = entry;

  if (bucket)
    *bucket = b;
  
  table->n_entries += 1;
823 824 825 826 827 828

  /* note we ONLY rebuild when ADDING - because you can iterate over a
   * table and remove entries safely.
   */
  if (table->n_entries >= table->hi_rebuild_size ||
      table->n_entries < table->lo_rebuild_size)
829
    rebuild_table (table);
830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856
}

static DBusHashEntry*
add_entry (DBusHashTable        *table, 
           unsigned int          idx,
           void                 *key,
           DBusHashEntry      ***bucket,
           DBusPreallocatedHash *preallocated)
{
  DBusHashEntry  *entry;

  if (preallocated == NULL)
    {
      entry = alloc_entry (table);
      if (entry == NULL)
        {
          if (bucket)
            *bucket = NULL;
          return NULL;
        }
    }
  else
    {
      entry = (DBusHashEntry*) preallocated;
    }

  add_allocated_entry (table, entry, idx, key, bucket);
857 858 859

  return entry;
}
860

861 862 863
/* This is g_str_hash from GLib which was
 * extensively discussed/tested/profiled
 */
864
static unsigned int
865
string_hash (const char *str)
866
{
867 868
  const char *p = str;
  unsigned int h = *p;
869

870 871 872
  if (h)
    for (p += 1; *p != '\0'; p++)
      h = (h << 5) - h + *p;
873

874 875 876
  return h;
}

877
#ifdef DBUS_BUILD_TESTS
878 879 880 881 882 883 884 885 886 887 888 889 890 891 892
/* This hashes a memory block with two nul-terminated strings
 * in it, used in dbus-object-registry.c at the moment.
 */
static unsigned int
two_strings_hash (const char *str)
{
  const char *p = str;
  unsigned int h = *p;

  if (h)
    for (p += 1; *p != '\0'; p++)
      h = (h << 5) - h + *p;

  for (p += 1; *p != '\0'; p++)
    h = (h << 5) - h + *p;
893
  
894
  return h;
895
}
896
#endif /* DBUS_BUILD_TESTS */
897

898
/** Key comparison function */
899 900
typedef int (* KeyCompareFunc) (const void *key_a, const void *key_b);

901
static DBusHashEntry*
902 903 904 905 906 907 908
find_generic_function (DBusHashTable        *table,
                       void                 *key,
                       unsigned int          idx,
                       KeyCompareFunc        compare_func,
                       dbus_bool_t           create_if_not_found,
                       DBusHashEntry      ***bucket,
                       DBusPreallocatedHash *preallocated)
909
{
910 911 912 913 914 915 916 917 918
  DBusHashEntry *entry;

  if (bucket)
    *bucket = NULL;

  /* Search all of the entries in this bucket. */
  entry = table->buckets[idx];
  while (entry != NULL)
    {
919 920
      if ((compare_func == NULL && key == entry->key) ||
          (compare_func != NULL && (* compare_func) (key, entry->key) == 0))
921 922 923
        {
          if (bucket)
            *bucket = &(table->buckets[idx]);
924 925 926 927

          if (preallocated)
            _dbus_hash_table_free_preallocated_entry (table, preallocated);
          
928 929 930 931 932
          return entry;
        }
      
      entry = entry->next;
    }
933

934
  if (create_if_not_found)
935 936 937
    entry = add_entry (table, idx, key, bucket, preallocated);
  else if (preallocated)
    _dbus_hash_table_free_preallocated_entry (table, preallocated);
938
  
939
  return entry;
940 941
}

942
static DBusHashEntry*
943
find_string_function (DBusHashTable        *table,
944 945 946 947
                      void                 *key,
                      dbus_bool_t           create_if_not_found,
                      DBusHashEntry      ***bucket,
                      DBusPreallocatedHash *preallocated)
948
{
949
  unsigned int idx;
950 951
  
  idx = string_hash (key) & table->mask;
952

953 954 955 956 957
  return find_generic_function (table, key, idx,
                                (KeyCompareFunc) strcmp, create_if_not_found, bucket,
                                preallocated);
}

958
#ifdef DBUS_BUILD_TESTS
959 960 961 962 963 964 965
static int
two_strings_cmp (const char *a,
                 const char *b)
{
  size_t len_a;
  size_t len_b;
  int res;
966
  
967 968 969
  res = strcmp (a, b);
  if (res != 0)
    return res;
970

971 972
  len_a = strlen (a);
  len_b = strlen (b);
973

974 975
  return strcmp (a + len_a + 1, b + len_b + 1);
}
976
#endif
977

978
#ifdef DBUS_BUILD_TESTS
979 980 981 982 983 984 985 986 987 988
static DBusHashEntry*
find_two_strings_function (DBusHashTable        *table,
                           void                 *key,
                           dbus_bool_t           create_if_not_found,
                           DBusHashEntry      ***bucket,
                           DBusPreallocatedHash *preallocated)
{
  unsigned int idx;
  
  idx = two_strings_hash (key) & table->mask;
989

990 991 992 993
  return find_generic_function (table, key, idx,
                                (KeyCompareFunc) two_strings_cmp, create_if_not_found, bucket,
                                preallocated);
}
994
#endif /* DBUS_BUILD_TESTS */
995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010

static DBusHashEntry*
find_direct_function (DBusHashTable        *table,
                      void                 *key,
                      dbus_bool_t           create_if_not_found,
                      DBusHashEntry      ***bucket,
                      DBusPreallocatedHash *preallocated)
{
  unsigned int idx;
  
  idx = RANDOM_INDEX (table, key) & table->mask;


  return find_generic_function (table, key, idx,
                                NULL, create_if_not_found, bucket,
                                preallocated);
1011
}
1012

1013 1014 1015 1016
static void
rebuild_table (DBusHashTable *table)
{
  int old_size;
1017
  int new_buckets;
1018 1019 1020
  DBusHashEntry **old_buckets;
  DBusHashEntry **old_chain;
  DBusHashEntry *entry;
1021 1022
  dbus_bool_t growing;
  
1023
  /*
1024 1025
   * Allocate and initialize the new bucket array, and set up
   * hashing constants for new array size.
1026
   */
1027 1028

  growing = table->n_entries >= table->hi_rebuild_size;
1029 1030 1031 1032
  
  old_size = table->n_buckets;
  old_buckets = table->buckets;

1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049
  if (growing)
    {
      /* overflow paranoia */
      if (table->n_buckets < _DBUS_INT_MAX / 4 &&
          table->down_shift >= 0)
        new_buckets = table->n_buckets * 4;
      else
        return; /* can't grow anymore */
    }
  else
    {
      new_buckets = table->n_buckets / 4;
      if (new_buckets < DBUS_SMALL_HASH_TABLE)
        return; /* don't bother shrinking this far */
    }

  table->buckets = dbus_new0 (DBusHashEntry*, new_buckets);
1050 1051 1052 1053 1054 1055 1056 1057
  if (table->buckets == NULL)
    {
      /* out of memory, yay - just don't reallocate, the table will
       * still work, albeit more slowly.
       */
      table->buckets = old_buckets;
      return;
    }
1058

1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076
  table->n_buckets = new_buckets;
  
  if (growing)
    {
      table->lo_rebuild_size = table->hi_rebuild_size;
      table->hi_rebuild_size *= 4;
      
      table->down_shift -= 2;               /* keep 2 more high bits */
      table->mask = (table->mask << 2) + 3; /* keep 2 more high bits */
    }
  else
    {
      table->hi_rebuild_size = table->lo_rebuild_size;
      table->lo_rebuild_size /= 4;

      table->down_shift += 2;         /* keep 2 fewer high bits */
      table->mask = table->mask >> 2; /* keep 2 fewer high bits */
    }
1077

1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092
#if 0
  printf ("%s table to lo = %d hi = %d downshift = %d mask = 0x%x\n",
          growing ? "GROW" : "SHRINK",
          table->lo_rebuild_size,
          table->hi_rebuild_size,
          table->down_shift,
          table->mask);
#endif
  
  _dbus_assert (table->lo_rebuild_size >= 0);
  _dbus_assert (table->hi_rebuild_size > table->lo_rebuild_size);
  _dbus_assert (table->mask != 0);
  /* the mask is essentially the max index */
  _dbus_assert (table->mask < table->n_buckets);
  
1093
  /*
1094
   * Rehash all of the existing entries into the new bucket array.
1095 1096
   */

1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109
  for (old_chain = old_buckets; old_size > 0; old_size--, old_chain++)
    {
      for (entry = *old_chain; entry != NULL; entry = *old_chain)
        {
          unsigned int idx;
          DBusHashEntry **bucket;
          
          *old_chain = entry->next;
          switch (table->key_type)
            {
            case DBUS_HASH_STRING:
              idx = string_hash (entry->key) & table->mask;
              break;
1110
            case DBUS_HASH_TWO_STRINGS:
1111
#ifdef DBUS_BUILD_TESTS
1112
              idx = two_strings_hash (entry->key) & table->mask;
1113 1114 1115 1116
#else
              idx = 0;
              _dbus_assert_not_reached ("two-strings is not enabled");
#endif
1117
              break;
1118
            case DBUS_HASH_INT:
1119
            case DBUS_HASH_ULONG:
1120
            case DBUS_HASH_POINTER:
1121 1122 1123 1124 1125 1126 1127
              idx = RANDOM_INDEX (table, entry->key);
              break;
            default:
              idx = 0;
              _dbus_assert_not_reached ("Unknown hash table type");
              break;
            }
1128
          
1129 1130 1131 1132 1133 1134 1135 1136 1137 1138
          bucket = &(table->buckets[idx]);
          entry->next = *bucket;
          *bucket = entry;
        }
    }
  
  /* Free the old bucket array, if it was dynamically allocated. */

  if (old_buckets != table->static_buckets)
    dbus_free (old_buckets);
1139 1140
}

1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152
/**
 * Looks up the value for a given string in a hash table
 * of type #DBUS_HASH_STRING. Returns %NULL if the value
 * is not present. (A not-present entry is indistinguishable
 * from an entry with a value of %NULL.)
 * @param table the hash table.
 * @param key the string to look up.
 * @returns the value of the hash entry.
 */
void*
_dbus_hash_table_lookup_string (DBusHashTable *table,
                                const char    *key)
1153
{
1154
  DBusHashEntry *entry;
1155

1156 1157
  _dbus_assert (table->key_type == DBUS_HASH_STRING);
  
1158
  entry = (* table->find_function) (table, (char*) key, FALSE, NULL, NULL);
1159

1160 1161 1162 1163 1164
  if (entry)
    return entry->value;
  else
    return NULL;
}
1165

1166
#ifdef DBUS_BUILD_TESTS
1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190
/**
 * Looks up the value for a given string in a hash table
 * of type #DBUS_HASH_TWO_STRINGS. Returns %NULL if the value
 * is not present. (A not-present entry is indistinguishable
 * from an entry with a value of %NULL.)
 * @param table the hash table.
 * @param key the string to look up.
 * @returns the value of the hash entry.
 */
void*
_dbus_hash_table_lookup_two_strings (DBusHashTable *table,
                                     const char    *key)
{
  DBusHashEntry *entry;

  _dbus_assert (table->key_type == DBUS_HASH_TWO_STRINGS);
  
  entry = (* table->find_function) (table, (char*) key, FALSE, NULL, NULL);

  if (entry)
    return entry->value;
  else
    return NULL;
}
1191
#endif /* DBUS_BUILD_TESTS */