libobjc/hash.c

/* Hash tables for Objective C internal structures
   Copyright (C) 1993, 1996, 1997, 2004 Free Software Foundation, Inc.

This file is part of GCC.

GCC 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, or (at your option)
any later version.

GCC 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 GCC; see the file COPYING.  If not, write to
the Free Software Foundation, 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.  */

/* As a special exception, if you link this library with files
   compiled with GCC to produce an executable, this does not cause
   the resulting executable to be covered by the GNU General Public License.
   This exception does not however invalidate any other reasons why
   the executable file might be covered by the GNU General Public License.  */

#include "assert.h"

#include "objc/hash.h"

#include "objc/runtime.h"		/* for DEBUG_PRINTF */

/* These two macros determine when a hash table is full and
   by how much it should be expanded respectively.

   These equations are percentages.  */
#define FULLNESS(cache) \
   ((((cache)->size * 75) / 100) <= (cache)->used)
#define EXPANSION(cache) \
  ((cache)->size * 2)

cache_ptr
objc_hash_new (unsigned int size, hash_func_type hash_func,
	       compare_func_type compare_func)
{
  cache_ptr cache;

  /* Pass me a value greater than 0 and a power of 2.  */
  assert (size);
  assert (! (size & (size - 1)));

  /* Allocate the cache structure.  calloc insures
     its initialization for default values.  */
  cache = (cache_ptr) objc_calloc (1, sizeof (struct cache));
  assert (cache);

  /* Allocate the array of buckets for the cache.
     calloc initializes all of the pointers to NULL.  */
  cache->node_table
    = (node_ptr *) objc_calloc (size, sizeof (node_ptr));
  assert (cache->node_table);

  cache->size  = size;

  /* This should work for all processor architectures? */
  cache->mask = (size - 1);
	
  /* Store the hashing function so that codes can be computed.  */
  cache->hash_func = hash_func;

  /* Store the function that compares hash keys to
     determine if they are equal.  */
  cache->compare_func = compare_func;

  return cache;
}


void
objc_hash_delete (cache_ptr cache)
{
  node_ptr node;
  node_ptr next_node;
  unsigned int i;

  /* Purge all key/value pairs from the table.  */
  /* Step through the nodes one by one and remove every node WITHOUT
     using objc_hash_next. this makes objc_hash_delete much more efficient. */
  for (i = 0;i < cache->size;i++) {
    if ((node = cache->node_table[i])) {
      /* an entry in the hash table has been found, now step through the
	 nodes next in the list and free them. */
      while ((next_node = node->next)) {
	objc_hash_remove (cache,node->key);
	node = next_node;
      }

      objc_hash_remove (cache,node->key);
    }
  }

  /* Release the array of nodes and the cache itself.  */
  objc_free(cache->node_table);
  objc_free(cache);
}


void
objc_hash_add (cache_ptr *cachep, const void *key, void *value)
{
  size_t indx = (*(*cachep)->hash_func)(*cachep, key);
  node_ptr node = (node_ptr) objc_calloc (1, sizeof (struct cache_node));


  assert (node);

  /* Initialize the new node.  */
  node->key    = key;
  node->value  = value;
  node->next  = (*cachep)->node_table[indx];

  /* Debugging.
     Check the list for another key.  */
#ifdef DEBUG
  { node_ptr node1 = (*cachep)->node_table[indx];

    while (node1) {

      assert (node1->key != key);
      node1 = node1->next;
    }
  }
#endif

  /* Install the node as the first element on the list.  */
  (*cachep)->node_table[indx] = node;

  /* Bump the number of entries in the cache.  */
  ++(*cachep)->used;

  /* Check the hash table's fullness.   We're going
     to expand if it is above the fullness level.  */
  if (FULLNESS (*cachep)) {

    /* The hash table has reached its fullness level.  Time to
       expand it.

       I'm using a slow method here but is built on other
       primitive functions thereby increasing its
       correctness.  */
    node_ptr node1 = NULL;
    cache_ptr new = objc_hash_new (EXPANSION (*cachep),
				   (*cachep)->hash_func,
				   (*cachep)->compare_func);

    DEBUG_PRINTF ("Expanding cache %#x from %d to %d\n",
		  (int) *cachep, (*cachep)->size, new->size);

    /* Copy the nodes from the first hash table to the new one.  */
    while ((node1 = objc_hash_next (*cachep, node1)))
      objc_hash_add (&new, node1->key, node1->value);

    /* Trash the old cache.  */
    objc_hash_delete (*cachep);

    /* Return a pointer to the new hash table.  */
    *cachep = new;
  }
}


void
objc_hash_remove (cache_ptr cache, const void *key)
{
  size_t indx = (*cache->hash_func)(cache, key);
  node_ptr node = cache->node_table[indx];


  /* We assume there is an entry in the table.  Error if it is not.  */
  assert (node);

  /* Special case.  First element is the key/value pair to be removed.  */
  if ((*cache->compare_func)(node->key, key)) {
    cache->node_table[indx] = node->next;
    objc_free(node);
  } else {

    /* Otherwise, find the hash entry.  */
    node_ptr prev = node;
    BOOL removed = NO;

    do {

      if ((*cache->compare_func)(node->key, key)) {
        prev->next = node->next, removed = YES;
        objc_free(node);
      } else
        prev = node, node = node->next;
    } while (! removed && node);
    assert (removed);
  }

  /* Decrement the number of entries in the hash table.  */
  --cache->used;
}


node_ptr
objc_hash_next (cache_ptr cache, node_ptr node)
{
  /* If the scan is being started then reset the last node
     visitied pointer and bucket index.  */
  if (! node)
    cache->last_bucket  = 0;

  /* If there is a node visited last then check for another
     entry in the same bucket;  Otherwise step to the next bucket.  */
  if (node) {
    if (node->next)
      /* There is a node which follows the last node
	 returned.  Step to that node and retun it.  */
      return node->next;
    else
      ++cache->last_bucket;
  }

  /* If the list isn't exhausted then search the buckets for
     other nodes.  */
  if (cache->last_bucket < cache->size) {
    /*  Scan the remainder of the buckets looking for an entry
	at the head of the list.  Return the first item found.  */
    while (cache->last_bucket < cache->size)
      if (cache->node_table[cache->last_bucket])
        return cache->node_table[cache->last_bucket];
      else
        ++cache->last_bucket;

    /* No further nodes were found in the hash table.  */
    return NULL;
  } else
    return NULL;
}


/* Given KEY, return corresponding value for it in CACHE.
   Return NULL if the KEY is not recorded.  */

void *
objc_hash_value_for_key (cache_ptr cache, const void *key)
{
  node_ptr node = cache->node_table[(*cache->hash_func)(cache, key)];
  void *retval = NULL;

  if (node)
    do {
      if ((*cache->compare_func)(node->key, key)) {
        retval = node->value;
              break;
      } else
        node = node->next;
    } while (! retval && node);

  return retval;
}

/* Given KEY, return YES if it exists in the CACHE.
   Return NO if it does not */

BOOL
objc_hash_is_key_in_hash (cache_ptr cache, const void *key)
{
  node_ptr node = cache->node_table[(*cache->hash_func)(cache, key)];

  if (node)
    do {
      if ((*cache->compare_func)(node->key, key))
	  return YES;
      else
        node = node->next;
    } while (node);

  return NO;
}