diff options
Diffstat (limited to 'hashmap.h')
| -rw-r--r-- | hashmap.h | 360 |
1 files changed, 324 insertions, 36 deletions
@@ -3,17 +3,123 @@ /* * Generic implementation of hash-based key-value mappings. - * See Documentation/technical/api-hashmap.txt. + * + * An example that maps long to a string: + * For the sake of the example this allows to lookup exact values, too + * (i.e. it is operated as a set, the value is part of the key) + * ------------------------------------- + * + * struct hashmap map; + * struct long2string { + * struct hashmap_entry ent; // must be the first member! + * long key; + * char value[FLEX_ARRAY]; // be careful with allocating on stack! + * }; + * + * #define COMPARE_VALUE 1 + * + * static int long2string_cmp(const struct long2string *e1, + * const struct long2string *e2, + * const void *keydata, const void *userdata) + * { + * char *string = keydata; + * unsigned *flags = (unsigned*)userdata; + * + * if (flags & COMPARE_VALUE) + * return !(e1->key == e2->key) || (keydata ? + * strcmp(e1->value, keydata) : strcmp(e1->value, e2->value)); + * else + * return !(e1->key == e2->key); + * } + * + * int main(int argc, char **argv) + * { + * long key; + * char *value, *action; + * + * unsigned flags = ALLOW_DUPLICATE_KEYS; + * + * hashmap_init(&map, (hashmap_cmp_fn) long2string_cmp, &flags, 0); + * + * while (scanf("%s %l %s", action, key, value)) { + * + * if (!strcmp("add", action)) { + * struct long2string *e; + * e = malloc(sizeof(struct long2string) + strlen(value)); + * hashmap_entry_init(e, memhash(&key, sizeof(long))); + * e->key = key; + * memcpy(e->value, value, strlen(value)); + * hashmap_add(&map, e); + * } + * + * if (!strcmp("print_all_by_key", action)) { + * flags &= ~COMPARE_VALUE; + * + * struct long2string k; + * hashmap_entry_init(&k, memhash(&key, sizeof(long))); + * k.key = key; + * + * struct long2string *e = hashmap_get(&map, &k, NULL); + * if (e) { + * printf("first: %l %s\n", e->key, e->value); + * while (e = hashmap_get_next(&map, e)) + * printf("found more: %l %s\n", e->key, e->value); + * } + * } + * + * if (!strcmp("has_exact_match", action)) { + * flags |= COMPARE_VALUE; + * + * struct long2string *e; + * e = malloc(sizeof(struct long2string) + strlen(value)); + * hashmap_entry_init(e, memhash(&key, sizeof(long))); + * e->key = key; + * memcpy(e->value, value, strlen(value)); + * + * printf("%s found\n", hashmap_get(&map, e, NULL) ? "" : "not"); + * } + * + * if (!strcmp("has_exact_match_no_heap_alloc", action)) { + * flags |= COMPARE_VALUE; + * + * struct long2string e; + * hashmap_entry_init(e, memhash(&key, sizeof(long))); + * e.key = key; + * + * printf("%s found\n", hashmap_get(&map, e, value) ? "" : "not"); + * } + * + * if (!strcmp("end", action)) { + * hashmap_free(&map, 1); + * break; + * } + * } + * } */ -/* FNV-1 functions */ - +/* + * Ready-to-use hash functions for strings, using the FNV-1 algorithm (see + * http://www.isthe.com/chongo/tech/comp/fnv). + * `strhash` and `strihash` take 0-terminated strings, while `memhash` and + * `memihash` operate on arbitrary-length memory. + * `strihash` and `memihash` are case insensitive versions. + * `memihash_cont` is a variant of `memihash` that allows a computation to be + * continued with another chunk of data. + */ extern unsigned int strhash(const char *buf); extern unsigned int strihash(const char *buf); extern unsigned int memhash(const void *buf, size_t len); extern unsigned int memihash(const void *buf, size_t len); extern unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len); +/* + * Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code + * for use in hash tables. Cryptographic hashes are supposed to have + * uniform distribution, so in contrast to `memhash()`, this just copies + * the first `sizeof(int)` bytes without shuffling any bits. Note that + * the results will be different on big-endian and little-endian + * platforms, so they should not be stored or transferred over the net. + */ static inline unsigned int sha1hash(const unsigned char *sha1) { /* @@ -25,86 +131,255 @@ static inline unsigned int sha1hash(const unsigned char *sha1) return hash; } -/* data structures */ - +/* + * struct hashmap_entry is an opaque structure representing an entry in the + * hash table, which must be used as first member of user data structures. + * Ideally it should be followed by an int-sized member to prevent unused + * memory on 64-bit systems due to alignment. + */ struct hashmap_entry { + /* + * next points to the next entry in case of collisions (i.e. if + * multiple entries map to the same bucket) + */ struct hashmap_entry *next; + + /* entry's hash code */ unsigned int hash; }; -typedef int (*hashmap_cmp_fn)(const void *entry, const void *entry_or_key, - const void *keydata); +/* + * User-supplied function to test two hashmap entries for equality. Shall + * return 0 if the entries are equal. + * + * This function is always called with non-NULL `entry` and `entry_or_key` + * parameters that have the same hash code. + * + * When looking up an entry, the `key` and `keydata` parameters to hashmap_get + * and hashmap_remove are always passed as second `entry_or_key` and third + * argument `keydata`, respectively. Otherwise, `keydata` is NULL. + * + * When it is too expensive to allocate a user entry (either because it is + * large or varialbe sized, such that it is not on the stack), then the + * relevant data to check for equality should be passed via `keydata`. + * In this case `key` can be a stripped down version of the user key data + * or even just a hashmap_entry having the correct hash. + * + * The `hashmap_cmp_fn_data` entry is the pointer given in the init function. + */ +typedef int (*hashmap_cmp_fn)(const void *hashmap_cmp_fn_data, + const void *entry, const void *entry_or_key, + const void *keydata); +/* + * struct hashmap is the hash table structure. Members can be used as follows, + * but should not be modified directly. + */ struct hashmap { struct hashmap_entry **table; + + /* Stores the comparison function specified in `hashmap_init()`. */ hashmap_cmp_fn cmpfn; - unsigned int size, tablesize, grow_at, shrink_at; - unsigned disallow_rehash : 1; -}; + const void *cmpfn_data; -struct hashmap_iter { - struct hashmap *map; - struct hashmap_entry *next; - unsigned int tablepos; + /* total number of entries (0 means the hashmap is empty) */ + unsigned int size; + + /* + * tablesize is the allocated size of the hash table. A non-0 value + * indicates that the hashmap is initialized. It may also be useful + * for statistical purposes (i.e. `size / tablesize` is the current + * load factor). + */ + unsigned int tablesize; + + unsigned int grow_at; + unsigned int shrink_at; + + /* See `hashmap_disallow_rehash`. */ + unsigned disallow_rehash : 1; }; /* hashmap functions */ -extern void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function, - size_t initial_size); +/* + * Initializes a hashmap structure. + * + * `map` is the hashmap to initialize. + * + * The `equals_function` can be specified to compare two entries for equality. + * If NULL, entries are considered equal if their hash codes are equal. + * + * The `equals_function_data` parameter can be used to provide additional data + * (a callback cookie) that will be passed to `equals_function` each time it + * is called. This allows a single `equals_function` to implement multiple + * comparison functions. + * + * If the total number of entries is known in advance, the `initial_size` + * parameter may be used to preallocate a sufficiently large table and thus + * prevent expensive resizing. If 0, the table is dynamically resized. + */ +extern void hashmap_init(struct hashmap *map, + hashmap_cmp_fn equals_function, + const void *equals_function_data, + size_t initial_size); + +/* + * Frees a hashmap structure and allocated memory. + * + * If `free_entries` is true, each hashmap_entry in the map is freed as well + * using stdlibs free(). + */ extern void hashmap_free(struct hashmap *map, int free_entries); /* hashmap_entry functions */ +/* + * Initializes a hashmap_entry structure. + * + * `entry` points to the entry to initialize. + * `hash` is the hash code of the entry. + * + * The hashmap_entry structure does not hold references to external resources, + * and it is safe to just discard it once you are done with it (i.e. if + * your structure was allocated with xmalloc(), you can just free(3) it, + * and if it is on stack, you can just let it go out of scope). + */ static inline void hashmap_entry_init(void *entry, unsigned int hash) { struct hashmap_entry *e = entry; e->hash = hash; e->next = NULL; } + +/* + * Returns the hashmap entry for the specified key, or NULL if not found. + * + * `map` is the hashmap structure. + * + * `key` is a user data structure that starts with hashmap_entry that has at + * least been initialized with the proper hash code (via `hashmap_entry_init`). + * + * `keydata` is a data structure that holds just enough information to check + * for equality to a given entry. + * + * If the key data is variable-sized (e.g. a FLEX_ARRAY string) or quite large, + * it is undesirable to create a full-fledged entry structure on the heap and + * copy all the key data into the structure. + * + * In this case, the `keydata` parameter can be used to pass + * variable-sized key data directly to the comparison function, and the `key` + * parameter can be a stripped-down, fixed size entry structure allocated on the + * stack. + * + * If an entry with matching hash code is found, `key` and `keydata` are passed + * to `hashmap_cmp_fn` to decide whether the entry matches the key. + */ extern void *hashmap_get(const struct hashmap *map, const void *key, - const void *keydata); -extern void *hashmap_get_next(const struct hashmap *map, const void *entry); -extern void hashmap_add(struct hashmap *map, void *entry); -extern void *hashmap_put(struct hashmap *map, void *entry); -extern void *hashmap_remove(struct hashmap *map, const void *key, - const void *keydata); + const void *keydata); +/* + * Returns the hashmap entry for the specified hash code and key data, + * or NULL if not found. + * + * `map` is the hashmap structure. + * `hash` is the hash code of the entry to look up. + * + * If an entry with matching hash code is found, `keydata` is passed to + * `hashmap_cmp_fn` to decide whether the entry matches the key. The + * `entry_or_key` parameter of `hashmap_cmp_fn` points to a hashmap_entry + * structure that should not be used in the comparison. + */ static inline void *hashmap_get_from_hash(const struct hashmap *map, - unsigned int hash, const void *keydata) + unsigned int hash, + const void *keydata) { struct hashmap_entry key; hashmap_entry_init(&key, hash); return hashmap_get(map, &key, keydata); } +/* + * Returns the next equal hashmap entry, or NULL if not found. This can be + * used to iterate over duplicate entries (see `hashmap_add`). + * + * `map` is the hashmap structure. + * `entry` is the hashmap_entry to start the search from, obtained via a previous + * call to `hashmap_get` or `hashmap_get_next`. + */ +extern void *hashmap_get_next(const struct hashmap *map, const void *entry); + +/* + * Adds a hashmap entry. This allows to add duplicate entries (i.e. + * separate values with the same key according to hashmap_cmp_fn). + * + * `map` is the hashmap structure. + * `entry` is the entry to add. + */ +extern void hashmap_add(struct hashmap *map, void *entry); + +/* + * Adds or replaces a hashmap entry. If the hashmap contains duplicate + * entries equal to the specified entry, only one of them will be replaced. + * + * `map` is the hashmap structure. + * `entry` is the entry to add or replace. + * Returns the replaced entry, or NULL if not found (i.e. the entry was added). + */ +extern void *hashmap_put(struct hashmap *map, void *entry); + +/* + * Removes a hashmap entry matching the specified key. If the hashmap contains + * duplicate entries equal to the specified key, only one of them will be + * removed. Returns the removed entry, or NULL if not found. + * + * Argument explanation is the same as in `hashmap_get`. + */ +extern void *hashmap_remove(struct hashmap *map, const void *key, + const void *keydata); + +/* + * Returns the `bucket` an entry is stored in. + * Useful for multithreaded read access. + */ int hashmap_bucket(const struct hashmap *map, unsigned int hash); /* * Disallow/allow rehashing of the hashmap. - * This is useful if the caller knows that the hashmap - * needs multi-threaded access. The caller is still - * required to guard/lock searches and inserts in a - * manner appropriate to their usage. This simply - * prevents the table from being unexpectedly re-mapped. + * This is useful if the caller knows that the hashmap needs multi-threaded + * access. The caller is still required to guard/lock searches and inserts + * in a manner appropriate to their usage. This simply prevents the table + * from being unexpectedly re-mapped. * - * If is up to the caller to ensure that the hashmap is - * initialized to a reasonable size to prevent poor - * performance. + * It is up to the caller to ensure that the hashmap is initialized to a + * reasonable size to prevent poor performance. * - * When value=1, prevent future rehashes on adds and deleted. - * When value=0, allow future rehahses. This DOES NOT force - * a rehash now. + * A call to allow rehashing does not force a rehash; that might happen + * with the next insert or delete. */ static inline void hashmap_disallow_rehash(struct hashmap *map, unsigned value) { map->disallow_rehash = value; } -/* hashmap_iter functions */ +/* + * Used to iterate over all entries of a hashmap. Note that it is + * not safe to add or remove entries to the hashmap while + * iterating. + */ +struct hashmap_iter { + struct hashmap *map; + struct hashmap_entry *next; + unsigned int tablepos; +}; +/* Initializes a `hashmap_iter` structure. */ extern void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter); + +/* Returns the next hashmap_entry, or NULL if there are no more entries. */ extern void *hashmap_iter_next(struct hashmap_iter *iter); + +/* Initializes the iterator and returns the first entry, if any. */ static inline void *hashmap_iter_first(struct hashmap *map, struct hashmap_iter *iter) { @@ -112,8 +387,21 @@ static inline void *hashmap_iter_first(struct hashmap *map, return hashmap_iter_next(iter); } -/* string interning */ +/* String interning */ +/* + * Returns the unique, interned version of the specified string or data, + * similar to the `String.intern` API in Java and .NET, respectively. + * Interned strings remain valid for the entire lifetime of the process. + * + * Can be used as `[x]strdup()` or `xmemdupz` replacement, except that interned + * strings / data must not be modified or freed. + * + * Interned strings are best used for short strings with high probability of + * duplicates. + * + * Uses a hashmap to store the pool of interned strings. + */ extern const void *memintern(const void *data, size_t len); static inline const char *strintern(const char *string) { |