hash.c

#include "nitfol.h"


/* Modified and bugfixed for nitfol by Evin Robertson Sept 10, 1999 */


/*
** public domain code by Jerry Coffin, with improvements by HenkJan Wolthuis.
**
** Tested with Visual C 1.0 and Borland C 3.1.
** Compiles without warnings, and seems like it should be pretty
** portable.
*/


#ifdef HEADER
/*
** A hash table consists of an array of these buckets.  Each bucket
** holds a copy of the key, a pointer to the data associated with the
** key, and a pointer to the next bucket that collided with this one,
** if there was one.
*/

typedef struct bucket {
    char *key;
    void *data;
    struct bucket *next;
} bucket;

/*
** This is what you actually declare an instance of to create a table.
** You then call 'construct_table' with the address of this structure,
** and a guess at the size of the table.  Note that more nodes than this
** can be inserted in the table, but performance degrades as this
** happens.  Performance should still be quite adequate until 2 or 3
** times as many nodes have been inserted as the table was created with.
*/

typedef struct hash_table {
    size_t size;
    bucket **table;
} hash_table;
#endif


/*
** These are used in freeing a table.  Perhaps I should code up
** something a little less grungy, but it works, so what the heck.
*/
typedef void (*my_function)(void *);
static my_function function = NULL;
static hash_table *the_table = NULL;

/* Initialize the hash_table to the size asked for.  Allocates space
** for the correct number of pointers and sets them to NULL.  If it
** can't allocate sufficient memory, signals error by setting the size
** of the table to 0.
*/

hash_table *n_hash_construct_table(hash_table *table, size_t size)
{
      size_t i;
      bucket **temp;

      table -> size  = size;
      table -> table = (bucket * *)n_malloc(sizeof(bucket *) * size);
      temp = table -> table;

      if ( temp == NULL )
      {
            table -> size = 0;
            return table;
      }

      for (i=0;i<size;i++)
            temp[i] = NULL;
      return table;
}


/*
** Hashes a string to produce an unsigned short, which should be
** sufficient for most purposes.
*/

static unsigned hash(const char *string)
{
      unsigned ret_val = 0;
      int i;

      while (*string)
      {
	    /* Modified by ecr to fix bug and improve method slightly */
            ret_val <<= 1;
            i = string[0] + (string[1] << 8);
            ret_val ^= i;
            string ++;
      }
      return ret_val;
}

/*
** Insert 'key' into hash table.
** Returns pointer to old data associated with the key, if any, or
** NULL if the key wasn't in the table previously.
*/

void *n_hash_insert(const char *key, void *data, hash_table *table)
{
      unsigned val = hash(key) % table->size;
      bucket *ptr;

      /*
      ** NULL means this bucket hasn't been used yet.  We'll simply
      ** allocate space for our new bucket and put our data there, with
      ** the table pointing at it.
      */

      if (NULL == (table->table)[val])
      {
            (table->table)[val] = (bucket *)n_malloc(sizeof(bucket));
            if (NULL==(table->table)[val])
                  return NULL;

            (table->table)[val] -> key = n_strdup(key);
            (table->table)[val] -> next = NULL;
            (table->table)[val] -> data = data;
            return (table->table)[val] -> data;
      }

      /*
      ** This spot in the table is already in use.  See if the current string
      ** has already been inserted, and if so, increment its count.
      */

      for (ptr = (table->table)[val];NULL != ptr; ptr = ptr -> next)
            if (0 == n_strcmp(key, ptr->key))
            {
                  void *old_data;

                  old_data = ptr->data;
                  ptr -> data = data;
                  return old_data;
            }

      /*
      ** This key must not be in the table yet.  We'll add it to the head of
      ** the list at this spot in the hash table.  Speed would be
      ** slightly improved if the list was kept sorted instead.  In this case,
      ** this code would be moved into the loop above, and the insertion would
      ** take place as soon as it was determined that the present key in the
      ** list was larger than this one.
      */

      ptr = (bucket *)n_malloc(sizeof(bucket));
      if (NULL==ptr)
            return 0;
      ptr -> key = n_strdup(key);
      ptr -> data = data;
      ptr -> next = (table->table)[val];
      (table->table)[val] = ptr;
      return data;
}


/*
** Look up a key and return the associated data.  Returns NULL if
** the key is not in the table.
*/

void *n_hash_lookup(const char *key, hash_table *table)
{
      unsigned val = hash(key) % table->size;
      bucket *ptr;

      if (NULL == (table->table)[val])
            return NULL;

      for ( ptr = (table->table)[val];NULL != ptr; ptr = ptr->next )
      {
            if (0 == n_strcmp(key, ptr -> key ) )
                  return ptr->data;
      }
      return NULL;
}

/*
** Delete a key from the hash table and return associated
** data, or NULL if not present.
*/

void *n_hash_del(const char *key, hash_table *table)
{
      unsigned val = hash(key) % table->size;
      void *data;
      bucket *ptr, *last = NULL;

      if (NULL == (table->table)[val])
            return NULL;

      /*
      ** Traverse the list, keeping track of the previous node in the list.
      ** When we find the node to delete, we set the previous node's next
      ** pointer to point to the node after ourself instead.  We then delete
      ** the key from the present node, and return a pointer to the data it
      ** contains.
      */

      for (last = NULL, ptr = (table->table)[val];
            NULL != ptr;
            last = ptr, ptr = ptr->next)
      {
            if (0 == n_strcmp(key, ptr -> key))
            {
                  if (last != NULL )
                  {
                        data = ptr -> data;
                        last -> next = ptr -> next;
                        n_free(ptr->key);
                        n_free(ptr);
                        return data;
                  }

                  /*
                  ** If 'last' still equals NULL, it means that we need to
                  ** delete the first node in the list. This simply consists
                  ** of putting our own 'next' pointer in the array holding
                  ** the head of the list.  We then dispose of the current
                  ** node as above.
                  */

                  else
                  {
                        data = ptr->data;
                        (table->table)[val] = ptr->next;
                        n_free(ptr->key);
                        n_free(ptr);
                        return data;
                  }
            }
      }

      /*
      ** If we get here, it means we didn't find the item in the table.
      ** Signal this by returning NULL.
      */

      return NULL;
}

/*
** free_table iterates the table, calling this repeatedly to free
** each individual node.  This, in turn, calls one or two other
** functions - one to free the storage used for the key, the other
** passes a pointer to the data back to a function defined by the user,
** process the data as needed.
*/

static void free_node(const char *key, void *data)
{
      (void) data;

      if (function)
            function(n_hash_del(key,the_table));
      else  n_hash_del(key,the_table);
}

/*
** Frees a complete table by iterating over it and freeing each node.
** the second parameter is the address of a function it will call with a
** pointer to the data associated with each node.  This function is
** responsible for freeing the data, or doing whatever is needed with
** it.
*/

void n_hash_free_table(hash_table *table, void (*func)(void *))
{
      function = func;
      the_table = table;

      n_hash_enumerate( table, free_node);
      n_free(table->table);
      table->table = NULL;
      table->size = 0;

      the_table = NULL;
      function = (void (*)(void *))NULL;
}

/*
** Simply invokes the function given as the second parameter for each
** node in the table, passing it the key and the associated data.
*/

void n_hash_enumerate( hash_table *table, void (*func)(const char *, void *))
{
      unsigned i;
      bucket *temp, *next;

      for (i=0; i < table->size; i++)
      {
	    for (temp = (table->table)[i]; temp; temp=next)
	    {
                   next = temp->next; /* ecr - temp may be deleted by func */
	           func(temp->key, temp->data);
	    }
      }
}