255 lines
6.8 KiB
C
255 lines
6.8 KiB
C
/* Hash tables for Objective C internal structures
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Copyright (C) 1993 Free Software Foundation, Inc.
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This file is part of GNU CC.
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GNU CC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU CC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU CC; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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#ifndef lint
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static char rcsid[] = "$Id: hash.c,v 1.2 1993/08/02 17:39:02 mycroft Exp $";
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#endif /* not lint */
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/* As a special exception, if you link this library with files
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compiled with GCC to produce an executable, this does not cause
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the resulting executable to be covered by the GNU General Public License.
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This exception does not however invalidate any other reasons why
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the executable file might be covered by the GNU General Public License. */
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#include "assert.h"
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#include "objc/hash.h"
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#include "objc/objc.h"
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#include "runtime.h" /* for DEBUG_PRINTF */
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/* These two macros determine when a hash table is full and
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by how much it should be expanded respectively.
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These equations are percentages. */
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#define FULLNESS(cache) \
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((((cache)->size * 75) / 100) <= (cache)->used)
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#define EXPANSION(cache) \
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((cache)->size * 2)
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cache_ptr
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hash_new (unsigned int size, hash_func_type hash_func,
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compare_func_type compare_func)
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{
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cache_ptr cache;
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/* Pass me a value greater than 0 and a power of 2. */
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assert (size);
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assert (!(size & (size - 1)));
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/* Allocate the cache structure. calloc insures
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its initialization for default values. */
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cache = (cache_ptr) __objc_xcalloc (1, sizeof (struct cache));
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assert (cache);
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/* Allocate the array of buckets for the cache.
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calloc initializes all of the pointers to NULL. */
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cache->node_table
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= (node_ptr *) __objc_xcalloc (size, sizeof (node_ptr));
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assert (cache->node_table);
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cache->size = size;
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/* This should work for all processor architectures? */
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cache->mask = (size - 1);
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/* Store the hashing function so that codes can be computed. */
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cache->hash_func = hash_func;
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/* Store the function that compares hash keys to
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determine if they are equal. */
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cache->compare_func = compare_func;
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return cache;
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}
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void
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hash_delete (cache_ptr cache)
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{
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node_ptr node;
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/* Purge all key/value pairs from the table. */
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while ((node = hash_next (cache, NULL)))
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hash_remove (cache, node->key);
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/* Release the array of nodes and the cache itself. */
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free (cache->node_table);
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free (cache);
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}
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void
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hash_add (cache_ptr *cachep, const void *key, void *value)
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{
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size_t indx = (*(*cachep)->hash_func)(*cachep, key);
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node_ptr node = (node_ptr) __objc_xcalloc (1, sizeof (struct cache_node));
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assert (node);
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/* Initialize the new node. */
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node->key = key;
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node->value = value;
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node->next = (*cachep)->node_table[indx];
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/* Debugging.
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Check the list for another key. */
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#ifdef DEBUG
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{ node_ptr node1 = (*cachep)->node_table[indx];
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while (node1) {
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assert (node1->key != key);
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node1 = node1->next;
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}
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}
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#endif
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/* Install the node as the first element on the list. */
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(*cachep)->node_table[indx] = node;
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/* Bump the number of entries in the cache. */
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++(*cachep)->used;
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/* Check the hash table's fullness. We're going
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to expand if it is above the fullness level. */
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if (FULLNESS (*cachep)) {
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/* The hash table has reached its fullness level. Time to
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expand it.
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I'm using a slow method here but is built on other
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primitive functions thereby increasing its
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correctness. */
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node_ptr node1 = NULL;
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cache_ptr new = hash_new (EXPANSION (*cachep),
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(*cachep)->hash_func,
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(*cachep)->compare_func);
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DEBUG_PRINTF ("Expanding cache %#x from %d to %d\n",
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*cachep, (*cachep)->size, new->size);
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/* Copy the nodes from the first hash table to the new one. */
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while ((node1 = hash_next (*cachep, node1)))
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hash_add (&new, node1->key, node1->value);
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/* Trash the old cache. */
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hash_delete (*cachep);
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/* Return a pointer to the new hash table. */
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*cachep = new;
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}
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}
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void
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hash_remove (cache_ptr cache, const void *key)
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{
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size_t indx = (*cache->hash_func)(cache, key);
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node_ptr node = cache->node_table[indx];
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/* We assume there is an entry in the table. Error if it is not. */
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assert (node);
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/* Special case. First element is the key/value pair to be removed. */
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if ((*cache->compare_func)(node->key, key)) {
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cache->node_table[indx] = node->next;
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free (node);
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} else {
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/* Otherwise, find the hash entry. */
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node_ptr prev = node;
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BOOL removed = NO;
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do {
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if ((*cache->compare_func)(node->key, key)) {
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prev->next = node->next, removed = YES;
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free (node);
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} else
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prev = node, node = node->next;
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} while (!removed && node);
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assert (removed);
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}
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/* Decrement the number of entries in the hash table. */
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--cache->used;
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}
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node_ptr
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hash_next (cache_ptr cache, node_ptr node)
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{
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/* If the scan is being started then reset the last node
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visitied pointer and bucket index. */
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if (!node)
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cache->last_bucket = 0;
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/* If there is a node visited last then check for another
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entry in the same bucket; Otherwise step to the next bucket. */
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if (node) {
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if (node->next)
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/* There is a node which follows the last node
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returned. Step to that node and retun it. */
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return node->next;
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else
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++cache->last_bucket;
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}
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/* If the list isn't exhausted then search the buckets for
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other nodes. */
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if (cache->last_bucket < cache->size) {
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/* Scan the remainder of the buckets looking for an entry
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at the head of the list. Return the first item found. */
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while (cache->last_bucket < cache->size)
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if (cache->node_table[cache->last_bucket])
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return cache->node_table[cache->last_bucket];
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else
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++cache->last_bucket;
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/* No further nodes were found in the hash table. */
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return NULL;
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} else
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return NULL;
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}
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/* Given KEY, return corresponding value for it in CACHE.
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Return NULL if the KEY is not recorded. */
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void *
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hash_value_for_key (cache_ptr cache, const void *key)
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{
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node_ptr node = cache->node_table[(*cache->hash_func)(cache, key)];
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void *retval = NULL;
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if (node)
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do {
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if ((*cache->compare_func)(node->key, key))
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retval = node->value;
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else
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node = node->next;
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} while (!retval && node);
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return retval;
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}
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