hashmap.c

   1 /*
   2  * Generic implementation of hash-based key value mappings.
   3  */
   4 #include "cache.h"
   5 #include "hashmap.h"
   6
   7 #define FNV32_BASE ((unsigned int) 0x811c9dc5)
   8 #define FNV32_PRIME ((unsigned int) 0x01000193)
   9
  10 unsigned int strhash(const char *str)
  11 {
  12         unsigned int c, hash = FNV32_BASE;
  13         while ((c = (unsigned char) *str++))
  14                 hash = (hash * FNV32_PRIME) ^ c;
  15         return hash;
  16 }
  17
  18 unsigned int strihash(const char *str)
  19 {
  20         unsigned int c, hash = FNV32_BASE;
  21         while ((c = (unsigned char) *str++)) {
  22                 if (c >= 'a' && c <= 'z')
  23                         c -= 'a' - 'A';
  24                 hash = (hash * FNV32_PRIME) ^ c;
  25         }
  26         return hash;
  27 }
  28
  29 unsigned int memhash(const void *buf, size_t len)
  30 {
  31         unsigned int hash = FNV32_BASE;
  32         unsigned char *ucbuf = (unsigned char *) buf;
  33         while (len--) {
  34                 unsigned int c = *ucbuf++;
  35                 hash = (hash * FNV32_PRIME) ^ c;
  36         }
  37         return hash;
  38 }
  39
  40 unsigned int memihash(const void *buf, size_t len)
  41 {
  42         unsigned int hash = FNV32_BASE;
  43         unsigned char *ucbuf = (unsigned char *) buf;
  44         while (len--) {
  45                 unsigned int c = *ucbuf++;
  46                 if (c >= 'a' && c <= 'z')
  47                         c -= 'a' - 'A';
  48                 hash = (hash * FNV32_PRIME) ^ c;
  49         }
  50         return hash;
  51 }
  52
  53 /*
  54  * Incoporate another chunk of data into a memihash
  55  * computation.
  56  */
  57 unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len)
  58 {
  59         unsigned int hash = hash_seed;
  60         unsigned char *ucbuf = (unsigned char *) buf;
  61         while (len--) {
  62                 unsigned int c = *ucbuf++;
  63                 if (c >= 'a' && c <= 'z')
  64                         c -= 'a' - 'A';
  65                 hash = (hash * FNV32_PRIME) ^ c;
  66         }
  67         return hash;
  68 }
  69
  70 #define HASHMAP_INITIAL_SIZE 64
  71 /* grow / shrink by 2^2 */
  72 #define HASHMAP_RESIZE_BITS 2
  73 /* load factor in percent */
  74 #define HASHMAP_LOAD_FACTOR 80
  75
  76 static void alloc_table(struct hashmap *map, unsigned int size)
  77 {
  78         map->tablesize = size;
  79         map->table = xcalloc(size, sizeof(struct hashmap_entry *));
  80
  81         /* calculate resize thresholds for new size */
  82         map->grow_at = (unsigned int) ((uint64_t) size * HASHMAP_LOAD_FACTOR / 100);
  83         if (size <= HASHMAP_INITIAL_SIZE)
  84                 map->shrink_at = 0;
  85         else
  86                 /*
  87                  * The shrink-threshold must be slightly smaller than
  88                  * (grow-threshold / resize-factor) to prevent erratic resizing,
  89                  * thus we divide by (resize-factor + 1).
  90                  */
  91                 map->shrink_at = map->grow_at / ((1 << HASHMAP_RESIZE_BITS) + 1);
  92 }
  93
  94 static inline int entry_equals(const struct hashmap *map,
  95                 const struct hashmap_entry *e1, const struct hashmap_entry *e2,
  96                 const void *keydata)
  97 {
  98         return (e1 == e2) || (e1->hash == e2->hash && !map->cmpfn(e1, e2, keydata));
  99 }
 100
 101 static inline unsigned int bucket(const struct hashmap *map,
 102                 const struct hashmap_entry *key)
 103 {
 104         return key->hash & (map->tablesize - 1);
 105 }
 106
 107 static void rehash(struct hashmap *map, unsigned int newsize)
 108 {
 109         unsigned int i, oldsize = map->tablesize;
 110         struct hashmap_entry **oldtable = map->table;
 111
 112         alloc_table(map, newsize);
 113         for (i = 0; i < oldsize; i++) {
 114                 struct hashmap_entry *e = oldtable[i];
 115                 while (e) {
 116                         struct hashmap_entry *next = e->next;
 117                         unsigned int b = bucket(map, e);
 118                         e->next = map->table[b];
 119                         map->table[b] = e;
 120                         e = next;
 121                 }
 122         }
 123         free(oldtable);
 124 }
 125
 126 static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
 127                 const struct hashmap_entry *key, const void *keydata)
 128 {
 129         struct hashmap_entry **e = &map->table[bucket(map, key)];
 130         while (*e && !entry_equals(map, *e, key, keydata))
 131                 e = &(*e)->next;
 132         return e;
 133 }
 134
 135 static int always_equal(const void *unused1, const void *unused2, const void *unused3)
 136 {
 137         return 0;
 138 }
 139
 140 void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
 141                 size_t initial_size)
 142 {
 143         unsigned int size = HASHMAP_INITIAL_SIZE;
 144         map->size = 0;
 145         map->cmpfn = equals_function ? equals_function : always_equal;
 146
 147         /* calculate initial table size and allocate the table */
 148         initial_size = (unsigned int) ((uint64_t) initial_size * 100
 149                         / HASHMAP_LOAD_FACTOR);
 150         while (initial_size > size)
 151                 size <<= HASHMAP_RESIZE_BITS;
 152         alloc_table(map, size);
 153 }
 154
 155 void hashmap_free(struct hashmap *map, int free_entries)
 156 {
 157         if (!map || !map->table)
 158                 return;
 159         if (free_entries) {
 160                 struct hashmap_iter iter;
 161                 struct hashmap_entry *e;
 162                 hashmap_iter_init(map, &iter);
 163                 while ((e = hashmap_iter_next(&iter)))
 164                         free(e);
 165         }
 166         free(map->table);
 167         memset(map, 0, sizeof(*map));
 168 }
 169
 170 void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)
 171 {
 172         return *find_entry_ptr(map, key, keydata);
 173 }
 174
 175 void *hashmap_get_next(const struct hashmap *map, const void *entry)
 176 {
 177         struct hashmap_entry *e = ((struct hashmap_entry *) entry)->next;
 178         for (; e; e = e->next)
 179                 if (entry_equals(map, entry, e, NULL))
 180                         return e;
 181         return NULL;
 182 }
 183
 184 void hashmap_add(struct hashmap *map, void *entry)
 185 {
 186         unsigned int b = bucket(map, entry);
 187
 188         /* add entry */
 189         ((struct hashmap_entry *) entry)->next = map->table[b];
 190         map->table[b] = entry;
 191
 192         /* fix size and rehash if appropriate */
 193         map->size++;
 194         if (map->size > map->grow_at)
 195                 rehash(map, map->tablesize << HASHMAP_RESIZE_BITS);
 196 }
 197
 198 void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)
 199 {
 200         struct hashmap_entry *old;
 201         struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
 202         if (!*e)
 203                 return NULL;
 204
 205         /* remove existing entry */
 206         old = *e;
 207         *e = old->next;
 208         old->next = NULL;
 209
 210         /* fix size and rehash if appropriate */
 211         map->size--;
 212         if (map->size < map->shrink_at)
 213                 rehash(map, map->tablesize >> HASHMAP_RESIZE_BITS);
 214         return old;
 215 }
 216
 217 void *hashmap_put(struct hashmap *map, void *entry)
 218 {
 219         struct hashmap_entry *old = hashmap_remove(map, entry, NULL);
 220         hashmap_add(map, entry);
 221         return old;
 222 }
 223
 224 void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)
 225 {
 226         iter->map = map;
 227         iter->tablepos = 0;
 228         iter->next = NULL;
 229 }
 230
 231 void *hashmap_iter_next(struct hashmap_iter *iter)
 232 {
 233         struct hashmap_entry *current = iter->next;
 234         for (;;) {
 235                 if (current) {
 236                         iter->next = current->next;
 237                         return current;
 238                 }
 239
 240                 if (iter->tablepos >= iter->map->tablesize)
 241                         return NULL;
 242
 243                 current = iter->map->table[iter->tablepos++];
 244         }
 245 }
 246
 247 struct pool_entry {
 248         struct hashmap_entry ent;
 249         size_t len;
 250         unsigned char data[FLEX_ARRAY];
 251 };
 252
 253 static int pool_entry_cmp(const struct pool_entry *e1,
 254                           const struct pool_entry *e2,
 255                           const unsigned char *keydata)
 256 {
 257         return e1->data != keydata &&
 258                (e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
 259 }
 260
 261 const void *memintern(const void *data, size_t len)
 262 {
 263         static struct hashmap map;
 264         struct pool_entry key, *e;
 265
 266         /* initialize string pool hashmap */
 267         if (!map.tablesize)
 268                 hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, 0);
 269
 270         /* lookup interned string in pool */
 271         hashmap_entry_init(&key, memhash(data, len));
 272         key.len = len;
 273         e = hashmap_get(&map, &key, data);
 274         if (!e) {
 275                 /* not found: create it */
 276                 FLEX_ALLOC_MEM(e, data, data, len);
 277                 hashmap_entry_init(e, key.ent.hash);
 278                 e->len = len;
 279                 hashmap_add(&map, e);
 280         }
 281         return e->data;
 282 }