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) ||
  99                (e1->hash == e2->hash &&
 100                 !map->cmpfn(map->cmpfn_data, e1, e2, keydata));
 101 }
 102
 103 static inline unsigned int bucket(const struct hashmap *map,
 104                 const struct hashmap_entry *key)
 105 {
 106         return key->hash & (map->tablesize - 1);
 107 }
 108
 109 int hashmap_bucket(const struct hashmap *map, unsigned int hash)
 110 {
 111         return hash & (map->tablesize - 1);
 112 }
 113
 114 static void rehash(struct hashmap *map, unsigned int newsize)
 115 {
 116         unsigned int i, oldsize = map->tablesize;
 117         struct hashmap_entry **oldtable = map->table;
 118
 119         if (map->disallow_rehash)
 120                 return;
 121
 122         alloc_table(map, newsize);
 123         for (i = 0; i < oldsize; i++) {
 124                 struct hashmap_entry *e = oldtable[i];
 125                 while (e) {
 126                         struct hashmap_entry *next = e->next;
 127                         unsigned int b = bucket(map, e);
 128                         e->next = map->table[b];
 129                         map->table[b] = e;
 130                         e = next;
 131                 }
 132         }
 133         free(oldtable);
 134 }
 135
 136 static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
 137                 const struct hashmap_entry *key, const void *keydata)
 138 {
 139         struct hashmap_entry **e = &map->table[bucket(map, key)];
 140         while (*e && !entry_equals(map, *e, key, keydata))
 141                 e = &(*e)->next;
 142         return e;
 143 }
 144
 145 static int always_equal(const void *unused_cmp_data,
 146                         const void *unused1,
 147                         const void *unused2,
 148                         const void *unused_keydata)
 149 {
 150         return 0;
 151 }
 152
 153 void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
 154                 const void *cmpfn_data, size_t initial_size)
 155 {
 156         unsigned int size = HASHMAP_INITIAL_SIZE;
 157
 158         memset(map, 0, sizeof(*map));
 159
 160         map->cmpfn = equals_function ? equals_function : always_equal;
 161         map->cmpfn_data = cmpfn_data;
 162
 163         /* calculate initial table size and allocate the table */
 164         initial_size = (unsigned int) ((uint64_t) initial_size * 100
 165                         / HASHMAP_LOAD_FACTOR);
 166         while (initial_size > size)
 167                 size <<= HASHMAP_RESIZE_BITS;
 168         alloc_table(map, size);
 169 }
 170
 171 void hashmap_free(struct hashmap *map, int free_entries)
 172 {
 173         if (!map || !map->table)
 174                 return;
 175         if (free_entries) {
 176                 struct hashmap_iter iter;
 177                 struct hashmap_entry *e;
 178                 hashmap_iter_init(map, &iter);
 179                 while ((e = hashmap_iter_next(&iter)))
 180                         free(e);
 181         }
 182         free(map->table);
 183         memset(map, 0, sizeof(*map));
 184 }
 185
 186 void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)
 187 {
 188         return *find_entry_ptr(map, key, keydata);
 189 }
 190
 191 void *hashmap_get_next(const struct hashmap *map, const void *entry)
 192 {
 193         struct hashmap_entry *e = ((struct hashmap_entry *) entry)->next;
 194         for (; e; e = e->next)
 195                 if (entry_equals(map, entry, e, NULL))
 196                         return e;
 197         return NULL;
 198 }
 199
 200 void hashmap_add(struct hashmap *map, void *entry)
 201 {
 202         unsigned int b = bucket(map, entry);
 203
 204         /* add entry */
 205         ((struct hashmap_entry *) entry)->next = map->table[b];
 206         map->table[b] = entry;
 207
 208         /* fix size and rehash if appropriate */
 209         map->size++;
 210         if (map->size > map->grow_at)
 211                 rehash(map, map->tablesize << HASHMAP_RESIZE_BITS);
 212 }
 213
 214 void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)
 215 {
 216         struct hashmap_entry *old;
 217         struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
 218         if (!*e)
 219                 return NULL;
 220
 221         /* remove existing entry */
 222         old = *e;
 223         *e = old->next;
 224         old->next = NULL;
 225
 226         /* fix size and rehash if appropriate */
 227         map->size--;
 228         if (map->size < map->shrink_at)
 229                 rehash(map, map->tablesize >> HASHMAP_RESIZE_BITS);
 230         return old;
 231 }
 232
 233 void *hashmap_put(struct hashmap *map, void *entry)
 234 {
 235         struct hashmap_entry *old = hashmap_remove(map, entry, NULL);
 236         hashmap_add(map, entry);
 237         return old;
 238 }
 239
 240 void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)
 241 {
 242         iter->map = map;
 243         iter->tablepos = 0;
 244         iter->next = NULL;
 245 }
 246
 247 void *hashmap_iter_next(struct hashmap_iter *iter)
 248 {
 249         struct hashmap_entry *current = iter->next;
 250         for (;;) {
 251                 if (current) {
 252                         iter->next = current->next;
 253                         return current;
 254                 }
 255
 256                 if (iter->tablepos >= iter->map->tablesize)
 257                         return NULL;
 258
 259                 current = iter->map->table[iter->tablepos++];
 260         }
 261 }
 262
 263 struct pool_entry {
 264         struct hashmap_entry ent;
 265         size_t len;
 266         unsigned char data[FLEX_ARRAY];
 267 };
 268
 269 static int pool_entry_cmp(const void *unused_cmp_data,
 270                           const struct pool_entry *e1,
 271                           const struct pool_entry *e2,
 272                           const unsigned char *keydata)
 273 {
 274         return e1->data != keydata &&
 275                (e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
 276 }
 277
 278 const void *memintern(const void *data, size_t len)
 279 {
 280         static struct hashmap map;
 281         struct pool_entry key, *e;
 282
 283         /* initialize string pool hashmap */
 284         if (!map.tablesize)
 285                 hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, NULL, 0);
 286
 287         /* lookup interned string in pool */
 288         hashmap_entry_init(&key, memhash(data, len));
 289         key.len = len;
 290         e = hashmap_get(&map, &key, data);
 291         if (!e) {
 292                 /* not found: create it */
 293                 FLEX_ALLOC_MEM(e, data, data, len);
 294                 hashmap_entry_init(e, key.ent.hash);
 295                 e->len = len;
 296                 hashmap_add(&map, e);
 297         }
 298         return e->data;
 299 }