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 #define HASHMAP_INITIAL_SIZE 64
  54 /* grow / shrink by 2^2 */
  55 #define HASHMAP_RESIZE_BITS 2
  56 /* load factor in percent */
  57 #define HASHMAP_LOAD_FACTOR 80
  58
  59 static void alloc_table(struct hashmap *map, unsigned int size)
  60 {
  61         map->tablesize = size;
  62         map->table = xcalloc(size, sizeof(struct hashmap_entry *));
  63
  64         /* calculate resize thresholds for new size */
  65         map->grow_at = (unsigned int) ((uint64_t) size * HASHMAP_LOAD_FACTOR / 100);
  66         if (size <= HASHMAP_INITIAL_SIZE)
  67                 map->shrink_at = 0;
  68         else
  69                 /*
  70                  * The shrink-threshold must be slightly smaller than
  71                  * (grow-threshold / resize-factor) to prevent erratic resizing,
  72                  * thus we divide by (resize-factor + 1).
  73                  */
  74                 map->shrink_at = map->grow_at / ((1 << HASHMAP_RESIZE_BITS) + 1);
  75 }
  76
  77 static inline int entry_equals(const struct hashmap *map,
  78                 const struct hashmap_entry *e1, const struct hashmap_entry *e2,
  79                 const void *keydata)
  80 {
  81         return (e1 == e2) || (e1->hash == e2->hash && !map->cmpfn(e1, e2, keydata));
  82 }
  83
  84 static inline unsigned int bucket(const struct hashmap *map,
  85                 const struct hashmap_entry *key)
  86 {
  87         return key->hash & (map->tablesize - 1);
  88 }
  89
  90 static void rehash(struct hashmap *map, unsigned int newsize)
  91 {
  92         unsigned int i, oldsize = map->tablesize;
  93         struct hashmap_entry **oldtable = map->table;
  94
  95         alloc_table(map, newsize);
  96         for (i = 0; i < oldsize; i++) {
  97                 struct hashmap_entry *e = oldtable[i];
  98                 while (e) {
  99                         struct hashmap_entry *next = e->next;
 100                         unsigned int b = bucket(map, e);
 101                         e->next = map->table[b];
 102                         map->table[b] = e;
 103                         e = next;
 104                 }
 105         }
 106         free(oldtable);
 107 }
 108
 109 static inline struct hashmap_entry **find_entry_ptr(const struct hashmap *map,
 110                 const struct hashmap_entry *key, const void *keydata)
 111 {
 112         struct hashmap_entry **e = &map->table[bucket(map, key)];
 113         while (*e && !entry_equals(map, *e, key, keydata))
 114                 e = &(*e)->next;
 115         return e;
 116 }
 117
 118 static int always_equal(const void *unused1, const void *unused2, const void *unused3)
 119 {
 120         return 0;
 121 }
 122
 123 void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
 124                 size_t initial_size)
 125 {
 126         unsigned int size = HASHMAP_INITIAL_SIZE;
 127         map->size = 0;
 128         map->cmpfn = equals_function ? equals_function : always_equal;
 129
 130         /* calculate initial table size and allocate the table */
 131         initial_size = (unsigned int) ((uint64_t) initial_size * 100
 132                         / HASHMAP_LOAD_FACTOR);
 133         while (initial_size > size)
 134                 size <<= HASHMAP_RESIZE_BITS;
 135         alloc_table(map, size);
 136 }
 137
 138 void hashmap_free(struct hashmap *map, int free_entries)
 139 {
 140         if (!map || !map->table)
 141                 return;
 142         if (free_entries) {
 143                 struct hashmap_iter iter;
 144                 struct hashmap_entry *e;
 145                 hashmap_iter_init(map, &iter);
 146                 while ((e = hashmap_iter_next(&iter)))
 147                         free(e);
 148         }
 149         free(map->table);
 150         memset(map, 0, sizeof(*map));
 151 }
 152
 153 void *hashmap_get(const struct hashmap *map, const void *key, const void *keydata)
 154 {
 155         return *find_entry_ptr(map, key, keydata);
 156 }
 157
 158 void *hashmap_get_next(const struct hashmap *map, const void *entry)
 159 {
 160         struct hashmap_entry *e = ((struct hashmap_entry *) entry)->next;
 161         for (; e; e = e->next)
 162                 if (entry_equals(map, entry, e, NULL))
 163                         return e;
 164         return NULL;
 165 }
 166
 167 void hashmap_add(struct hashmap *map, void *entry)
 168 {
 169         unsigned int b = bucket(map, entry);
 170
 171         /* add entry */
 172         ((struct hashmap_entry *) entry)->next = map->table[b];
 173         map->table[b] = entry;
 174
 175         /* fix size and rehash if appropriate */
 176         map->size++;
 177         if (map->size > map->grow_at)
 178                 rehash(map, map->tablesize << HASHMAP_RESIZE_BITS);
 179 }
 180
 181 void *hashmap_remove(struct hashmap *map, const void *key, const void *keydata)
 182 {
 183         struct hashmap_entry *old;
 184         struct hashmap_entry **e = find_entry_ptr(map, key, keydata);
 185         if (!*e)
 186                 return NULL;
 187
 188         /* remove existing entry */
 189         old = *e;
 190         *e = old->next;
 191         old->next = NULL;
 192
 193         /* fix size and rehash if appropriate */
 194         map->size--;
 195         if (map->size < map->shrink_at)
 196                 rehash(map, map->tablesize >> HASHMAP_RESIZE_BITS);
 197         return old;
 198 }
 199
 200 void *hashmap_put(struct hashmap *map, void *entry)
 201 {
 202         struct hashmap_entry *old = hashmap_remove(map, entry, NULL);
 203         hashmap_add(map, entry);
 204         return old;
 205 }
 206
 207 void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter)
 208 {
 209         iter->map = map;
 210         iter->tablepos = 0;
 211         iter->next = NULL;
 212 }
 213
 214 void *hashmap_iter_next(struct hashmap_iter *iter)
 215 {
 216         struct hashmap_entry *current = iter->next;
 217         for (;;) {
 218                 if (current) {
 219                         iter->next = current->next;
 220                         return current;
 221                 }
 222
 223                 if (iter->tablepos >= iter->map->tablesize)
 224                         return NULL;
 225
 226                 current = iter->map->table[iter->tablepos++];
 227         }
 228 }
 229
 230 struct pool_entry {
 231         struct hashmap_entry ent;
 232         size_t len;
 233         unsigned char data[FLEX_ARRAY];
 234 };
 235
 236 static int pool_entry_cmp(const struct pool_entry *e1,
 237                           const struct pool_entry *e2,
 238                           const unsigned char *keydata)
 239 {
 240         return e1->data != keydata &&
 241                (e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
 242 }
 243
 244 const void *memintern(const void *data, size_t len)
 245 {
 246         static struct hashmap map;
 247         struct pool_entry key, *e;
 248
 249         /* initialize string pool hashmap */
 250         if (!map.tablesize)
 251                 hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, 0);
 252
 253         /* lookup interned string in pool */
 254         hashmap_entry_init(&key, memhash(data, len));
 255         key.len = len;
 256         e = hashmap_get(&map, &key, data);
 257         if (!e) {
 258                 /* not found: create it */
 259                 e = xmallocz(sizeof(struct pool_entry) + len);
 260                 hashmap_entry_init(e, key.ent.hash);
 261                 e->len = len;
 262                 memcpy(e->data, data, len);
 263                 hashmap_add(&map, e);
 264         }
 265         return e->data;
 266 }