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Annotation of gcc/objc/hash.c, revision 1.1

1.1     ! root        1: /* Hash tables for Objective C method dispatch.
        !             2:    Copyright (C) 1992 Free Software Foundation, Inc.
        !             3: 
        !             4: This file is part of GNU CC.
        !             5: 
        !             6: GNU CC is free software; you can redistribute it and/or modify
        !             7: it under the terms of the GNU General Public License as published by
        !             8: the Free Software Foundation; either version 2, or (at your option)
        !             9: any later version.
        !            10: 
        !            11: GNU CC is distributed in the hope that it will be useful,
        !            12: but WITHOUT ANY WARRANTY; without even the implied warranty of
        !            13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        !            14: GNU General Public License for more details.
        !            15: 
        !            16: You should have received a copy of the GNU General Public License
        !            17: along with GNU CC; see the file COPYING.  If not, write to
        !            18: the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
        !            19: 
        !            20: /* As a special exception, if you link this library with files
        !            21:    compiled with GCC to produce an executable, this does not cause
        !            22:    the resulting executable to be covered by the GNU General Public License.
        !            23:    This exception does not however invalidate any other reasons why
        !            24:    the executable file might be covered by the GNU General Public License.  */
        !            25: 
        !            26: #include "tconfig.h"
        !            27: #include "gstddef.h"
        !            28: #include "gstdarg.h"
        !            29: #include "assert.h"
        !            30: 
        !            31: #include "hash.h"
        !            32: #include "objc.h"
        !            33: #include "objc-proto.h"
        !            34: 
        !            35: 
        !            36: /* These two macros determine when a hash table is full and
        !            37:    by how much it should be expanded respectively.
        !            38: 
        !            39:    These equations are percentages.  */
        !            40: #define FULLNESS(cache) \
        !            41:    ((((cache)->size * 75) / 100) <= (cache)->used)
        !            42: #define EXPANSION(cache) \
        !            43:   ((cache)->size * 2)
        !            44: 
        !            45: cache_ptr
        !            46: hash_new (unsigned int size, hash_func_type hash_func,
        !            47:          compare_func_type compare_func)
        !            48: {
        !            49:   cache_ptr cache;
        !            50: 
        !            51: 
        !            52:   /* Pass me a value greater than 0 and a power of 2.  */
        !            53:   assert (size);
        !            54:   assert (!(size & (size - 1)));
        !            55: 
        !            56:   /* Allocate the cache structure.  calloc insures
        !            57:      its initialization for default values.  */
        !            58:   cache = (cache_ptr) calloc (1, sizeof (struct cache));
        !            59:   assert (cache);
        !            60: 
        !            61:   /* Allocate the array of buckets for the cache.
        !            62:      calloc initializes all of the pointers to NULL.  */
        !            63:   cache->node_table
        !            64:     = (node_ptr *) calloc (size, sizeof (node_ptr));
        !            65:   assert (cache->node_table);
        !            66: 
        !            67:   cache->size  = size;
        !            68: 
        !            69:   /* This should work for all processor architectures? */
        !            70:   cache->mask = (size - 1);
        !            71:        
        !            72:   /* Store the hashing function so that codes can be computed.  */
        !            73:   cache->hash_func = hash_func;
        !            74: 
        !            75:   /* Store the function that compares hash keys to
        !            76:      determine if they are equal.  */
        !            77:   cache->compare_func = compare_func;
        !            78: 
        !            79:   return cache;
        !            80: }
        !            81: 
        !            82: 
        !            83: void
        !            84: hash_delete (cache_ptr cache)
        !            85: {
        !            86:   node_ptr node;
        !            87: 
        !            88: 
        !            89:   /* Purge all key/value pairs from the table.  */
        !            90:   while (node = hash_next (cache, NULL))
        !            91:     hash_remove (cache, node->key);
        !            92: 
        !            93:   /* Release the array of nodes and the cache itself.  */
        !            94:   free (cache->node_table);
        !            95:   free (cache);
        !            96: }
        !            97: 
        !            98: 
        !            99: void
        !           100: hash_add (cache_ptr *cachep, const void *key, void *value)
        !           101: {
        !           102:   size_t indx = (*(*cachep)->hash_func)(*cachep, key);
        !           103:   node_ptr node = (node_ptr) calloc (1, sizeof (struct cache_node));
        !           104: 
        !           105: 
        !           106:   assert (node);
        !           107: 
        !           108:   /* Initialize the new node.  */
        !           109:   node->key    = key;
        !           110:   node->value  = value;
        !           111:   node->next  = (*cachep)->node_table[indx];
        !           112: 
        !           113:   /* Debugging.
        !           114:      Check the list for another key.  */
        !           115: #ifdef DEBUG
        !           116:   { node_ptr node1 = (*cachep)->node_table[indx];
        !           117: 
        !           118:     while (node1) {
        !           119: 
        !           120:       assert (node1->key != key);
        !           121:       node1 = node1->next;
        !           122:     }
        !           123:   }
        !           124: #endif
        !           125: 
        !           126:   /* Install the node as the first element on the list.  */
        !           127:   (*cachep)->node_table[indx] = node;
        !           128: 
        !           129:   /* Bump the number of entries in the cache.  */
        !           130:   ++(*cachep)->used;
        !           131: 
        !           132:   /* Check the hash table's fullness.   We're going
        !           133:      to expand if it is above the fullness level.  */
        !           134:   if (FULLNESS (*cachep)) {
        !           135: 
        !           136:     /* The hash table has reached its fullness level.  Time to
        !           137:        expand it.
        !           138: 
        !           139:        I'm using a slow method here but is built on other
        !           140:        primitive functions thereby increasing its
        !           141:        correctness.  */
        !           142:     node_ptr node1 = NULL;
        !           143:     cache_ptr new = hash_new (EXPANSION (*cachep),
        !           144:                              (*cachep)->hash_func,
        !           145:                              (*cachep)->compare_func);
        !           146: 
        !           147:     DEBUG_PRINTF ("Expanding cache %#x from %d to %d\n",
        !           148:                  *cachep, (*cachep)->size, new->size);
        !           149: 
        !           150:     /* Copy the nodes from the first hash table to the new one.  */
        !           151:     while (node1 = hash_next (*cachep, node1))
        !           152:       hash_add (&new, node1->key, node1->value);
        !           153: 
        !           154:     /* Trash the old cache.  */
        !           155:     hash_delete (*cachep);
        !           156: 
        !           157:     /* Return a pointer to the new hash table.  */
        !           158:     *cachep = new;
        !           159:   }
        !           160: }
        !           161: 
        !           162: 
        !           163: void
        !           164: hash_remove (cache_ptr cache, const void *key)
        !           165: {
        !           166:   size_t indx = (*cache->hash_func)(cache, key);
        !           167:   node_ptr node = cache->node_table[indx];
        !           168: 
        !           169: 
        !           170:   /* We assume there is an entry in the table.  Error if it is not.  */
        !           171:   assert (node);
        !           172: 
        !           173:   /* Special case.  First element is the key/value pair to be removed.  */
        !           174:   if ((*cache->compare_func)(node->key, key)) {
        !           175:     cache->node_table[indx] = node->next;
        !           176:     free (node);
        !           177:   } else {
        !           178: 
        !           179:     /* Otherwise, find the hash entry.  */
        !           180:     node_ptr prev = node;
        !           181:     BOOL removed = NO;
        !           182: 
        !           183:     do {
        !           184: 
        !           185:       if ((*cache->compare_func)(node->key, key)) {
        !           186:         prev->next = node->next, removed = YES;
        !           187:         free (node);
        !           188:       } else
        !           189:         prev = node, node = node->next;
        !           190:     } while (!removed && node);
        !           191:     assert (removed);
        !           192:   }
        !           193: 
        !           194:   /* Decrement the number of entries in the hash table.  */
        !           195:   --cache->used;
        !           196: }
        !           197: 
        !           198: 
        !           199: node_ptr
        !           200: hash_next (cache_ptr cache, node_ptr node)
        !           201: {
        !           202:   /* If the scan is being started then reset the last node
        !           203:      visitied pointer and bucket index.  */
        !           204:   if (!node)
        !           205:     cache->last_bucket  = 0;
        !           206: 
        !           207:   /* If there is a node visited last then check for another
        !           208:      entry in the same bucket;  Otherwise step to the next bucket.  */
        !           209:   if (node) {
        !           210:     if (node->next)
        !           211:       /* There is a node which follows the last node
        !           212:         returned.  Step to that node and retun it.  */
        !           213:       return node->next;
        !           214:     else
        !           215:       ++cache->last_bucket;
        !           216:   }
        !           217: 
        !           218:   /* If the list isn't exhausted then search the buckets for
        !           219:      other nodes.  */
        !           220:   if (cache->last_bucket < cache->size) {
        !           221:     /*  Scan the remainder of the buckets looking for an entry
        !           222:        at the head of the list.  Return the first item found.  */
        !           223:     while (cache->last_bucket < cache->size)
        !           224:       if (cache->node_table[cache->last_bucket])
        !           225:         return cache->node_table[cache->last_bucket];
        !           226:       else
        !           227:         ++cache->last_bucket;
        !           228: 
        !           229:     /* No further nodes were found in the hash table.  */
        !           230:     return NULL;
        !           231:   } else
        !           232:     return NULL;
        !           233: }
        !           234: 
        !           235: 
        !           236: /* Given KEY, return corresponding value for it in CACHE.
        !           237:    Return NULL if the KEY is not recorded.  */
        !           238: 
        !           239: void *
        !           240: hash_value_for_key (cache_ptr cache, const void *key)
        !           241: {
        !           242:   node_ptr node = cache->node_table[(*cache->hash_func)(cache, key)];
        !           243:   void *retval = NULL;
        !           244: 
        !           245:   if (node)
        !           246:     do {
        !           247:       if ((*cache->compare_func)(node->key, key))
        !           248:         retval = node->value;
        !           249:       else
        !           250:         node = node->next;
        !           251:     } while (!retval && node);
        !           252: 
        !           253:   return retval;
        !           254: }

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