File: dict.c

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/*
   dict.c - dictionary functions
   This file is part of the nss-pam-ldapd library.

   Copyright (C) 2007, 2008, 2009, 2010, 2012, 2013 Arthur de Jong

   This library 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 library 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 library; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   02110-1301 USA
*/

#include "config.h"

#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <ctype.h>
#ifdef HAVE_STDINT_H
#include <stdint.h>
#endif /* HAVE_STDINT_H */

#include "dict.h"

/*
   This module uses a hashtable to store its key to value mappings. The
   structure is basically as follows:

   [struct dictionary]
     \- holds an array of pointers to a linked list of [struct dict_entry]
          \- each entry has a key/value mapping

   The hashmap can be resized when the total number of elements in the hashmap
   exceeds a certain load factor.

   All the keys are copied in a separate linked list of buffers where each new
   buffer that is allocated is larger than the previous one. The first buffer
   in the linked list is always the current one.
*/

/* an entry stores one key/value pair */
struct dict_entry {
  uint32_t hash;      /* used for quick matching and rehashing */
  const char *key;    /* a reference to a copy of the key */
  void *value;        /* the stored value */
  struct dict_entry *next;
};

/* the initial size of the hashtable */
#define DICT_INITSIZE 7

/* load factor at which point to grow hashtable */
#define DICT_LOADPERCENTAGE 400

/* the dictionary is a hashtable */
struct dictionary {
  int size;                      /* size of the hashtable */
  int num;                       /* total number of keys stored */
  struct dict_entry **table;     /* the hashtable */
};

/* Simple hash function that computes the hash value of a string. */
static uint32_t stringhash(const char *str)
{
  uint32_t hash = 5381;
  uint32_t c;
  while ((c = *str++) != '\0')
    hash = 33 * hash + c;
  return hash;
}

/* Grow the hashtable. */
static void growhashtable(DICT *dict)
{
  int i;
  int newsize;
  struct dict_entry **newtable;
  struct dict_entry *entry, *tmp;
  newsize = dict->size * 3 + 1;
  /* allocate room for new hashtable */
  newtable = (struct dict_entry **)malloc(newsize * sizeof(struct dict_entry *));
  if (newtable == NULL)
    return; /* allocating memory failed continue to fill the existing table */
  /* clear new table */
  for (i = 0; i < newsize; i++)
    newtable[i] = NULL;
  /* copy old hashtable into new table */
  for (i = 0; i < dict->size; i++)
  {
    /* go over elements in linked list */
    entry = dict->table[i];
    while (entry != NULL)
    {
      tmp = entry;
      entry = entry->next;
      /* put in new position */
      tmp->next = newtable[tmp->hash % newsize];
      newtable[tmp->hash % newsize] = tmp;
    }
  }
  /* free the old hashtable */
  free(dict->table);
  /* put new hashtable in place */
  dict->size = newsize;
  dict->table = newtable;
}

DICT *dict_new(void)
{
  struct dictionary *dict;
  int i;
  /* allocate room for dictionary information */
  dict = (struct dictionary *)malloc(sizeof(struct dictionary));
  if (dict == NULL)
    return NULL;
  dict->size = DICT_INITSIZE;
  dict->num = 0;
  /* allocate initial hashtable */
  dict->table = (struct dict_entry **)malloc(DICT_INITSIZE * sizeof(struct dict_entry *));
  if (dict->table == NULL)
  {
    free(dict);
    return NULL;
  }
  /* clear the hashtable */
  for (i = 0; i < DICT_INITSIZE; i++)
    dict->table[i] = NULL;
  /* we're done */
  return dict;
}

void dict_free(DICT *dict)
{
  struct dict_entry *entry, *etmp;
  int i;
  /* free hashtable entries */
  for (i = 0; i < dict->size; i++)
  {
    entry = dict->table[i];
    while (entry != NULL)
    {
      etmp = entry;
      entry = entry->next;
      free(etmp);
    }
  }
  /* free the hashtable */
  free(dict->table);
  /* free dictionary struct itself */
  free(dict);
}

void *dict_get(DICT *dict, const char *key)
{
  uint32_t hash;
  struct dict_entry *entry;
  /* calculate the hash */
  hash = stringhash(key);
  /* loop over the linked list in the hashtable */
  for (entry = dict->table[hash % dict->size]; entry != NULL; entry = entry->next)
  {
    if ((entry->hash == hash) && (strcmp(entry->key, key) == 0))
      return entry->value;
  }
  /* no matches found */
  return NULL;
}

const char *dict_getany(DICT *dict)
{
  int i;
  /* loop over the linked list in the hashtable */
  for (i = 0; i < dict->size; i++)
    if (dict->table[i])
      return dict->table[i]->key;
  /* no matches found */
  return NULL;
}

int dict_put(DICT *dict, const char *key, void *value)
{
  uint32_t hash;
  int l;
  char *buf;
  int idx;
  struct dict_entry *entry, *prev;
  /* check if we should grow the hashtable */
  if (dict->num >= ((dict->size * DICT_LOADPERCENTAGE) / 100))
    growhashtable(dict);
  /* calculate the hash and position in the hashtable */
  hash = stringhash(key);
  idx = hash % dict->size;
  /* check if the entry is already present */
  for (entry = dict->table[idx], prev = NULL; entry != NULL; prev = entry, entry = entry->next)
  {
    if ((entry->hash == hash) && (strcmp(entry->key, key) == 0))
    {
      /* check if we should unset the entry */
      if (value == NULL)
      {
        /* remove from linked list */
        if (prev == NULL)
          dict->table[idx] = entry->next;
        else
          prev->next = entry->next;
        /* free entry memory and register removal */
        free(entry);
        dict->num--;
        return 0;
      }
      /* just set the new value */
      entry->value = value;
      return 0;
    }
  }
  /* if entry should be unset we're done */
  if (value == NULL)
    return 0;
  /* entry is not present, make new entry */
  l = strlen(key) + 1;
  buf = (char *)malloc(sizeof(struct dict_entry) + l);
  if (buf == NULL)
    return -1;
  entry = (struct dict_entry *)(void *)buf;
  buf += sizeof(struct dict_entry);
  strcpy(buf, key);
  entry->hash = hash;
  entry->key = buf;
  entry->value = value;
  /* insert into hashtable/linked list */
  entry->next = dict->table[idx];
  dict->table[idx] = entry;
  /* increment number of stored items */
  dict->num++;
  return 0;
}

const char **dict_keys(DICT *dict)
{
  int i;
  struct dict_entry *entry;
  char *buf;
  const char **values;
  size_t sz;
  int num;
  /* figure out how much memory to allocate */
  num = 0;
  sz = 0;
  for (i = 0; i < dict->size; i++)
  {
    entry = dict->table[i];
    while (entry != NULL)
    {
      num++;
      sz += strlen(entry->key) + 1;
      entry = entry->next;
    }
  }
  /* allocate the needed memory */
  buf = (char *)malloc((num + 1) * sizeof(char *) + sz);
  if (buf == NULL)
    return NULL;
  values = (const char **)(void *)buf;
  buf += (num + 1) * sizeof(char *);
  /* fill the array with the keys */
  num = 0;
  for (i = 0; i < dict->size; i++)
  {
    entry = dict->table[i];
    while (entry != NULL)
    {
      strcpy(buf, entry->key);
      values[num++] = buf;
      buf += strlen(buf) + 1;
      entry = entry->next;
    }
  }
  values[num] = NULL;
  /* done */
  return values;
}