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Diffstat (limited to 'hashmap.h')
| -rw-r--r-- | hashmap.h | 440 |
1 files changed, 440 insertions, 0 deletions
diff --git a/hashmap.h b/hashmap.h new file mode 100644 index 000000000000..84249115664b --- /dev/null +++ b/hashmap.h @@ -0,0 +1,440 @@ +#ifndef HASHMAP_H +#define HASHMAP_H + +#include "hash.h" + +/* + * Generic implementation of hash-based key-value mappings. + * + * 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 void *hashmap_cmp_fn_data, + * const struct long2string *e1, + * const struct long2string *e2, + * const void *keydata) + * { + * const char *string = keydata; + * unsigned flags = *(unsigned *)hashmap_cmp_fn_data; + * + * if (flags & COMPARE_VALUE) + * return e1->key != e2->key || + * strcmp(e1->value, string ? string : e2->value); + * else + * return e1->key != e2->key; + * } + * + * int main(int argc, char **argv) + * { + * long key; + * char value[255], action[32]; + * unsigned flags = 0; + * + * hashmap_init(&map, (hashmap_cmp_fn) long2string_cmp, &flags, 0); + * + * while (scanf("%s %ld %s", action, &key, value)) { + * + * if (!strcmp("add", action)) { + * struct long2string *e; + * FLEX_ALLOC_STR(e, value, value); + * hashmap_entry_init(e, memhash(&key, sizeof(long))); + * e->key = key; + * hashmap_add(&map, e); + * } + * + * if (!strcmp("print_all_by_key", action)) { + * struct long2string k, *e; + * hashmap_entry_init(&k, memhash(&key, sizeof(long))); + * k.key = key; + * + * flags &= ~COMPARE_VALUE; + * e = hashmap_get(&map, &k, NULL); + * if (e) { + * printf("first: %ld %s\n", e->key, e->value); + * while ((e = hashmap_get_next(&map, e))) + * printf("found more: %ld %s\n", e->key, e->value); + * } + * } + * + * if (!strcmp("has_exact_match", action)) { + * struct long2string *e; + * FLEX_ALLOC_STR(e, value, value); + * hashmap_entry_init(e, memhash(&key, sizeof(long))); + * e->key = key; + * + * flags |= COMPARE_VALUE; + * printf("%sfound\n", hashmap_get(&map, e, NULL) ? "" : "not "); + * free(e); + * } + * + * if (!strcmp("has_exact_match_no_heap_alloc", action)) { + * struct long2string k; + * hashmap_entry_init(&k, memhash(&key, sizeof(long))); + * k.key = key; + * + * flags |= COMPARE_VALUE; + * printf("%sfound\n", hashmap_get(&map, &k, value) ? "" : "not "); + * } + * + * if (!strcmp("end", action)) { + * hashmap_free(&map, 1); + * break; + * } + * } + * + * return 0; + * } + */ + +/* + * 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. + */ +unsigned int strhash(const char *buf); +unsigned int strihash(const char *buf); +unsigned int memhash(const void *buf, size_t len); +unsigned int memihash(const void *buf, size_t len); +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 oidhash(const struct object_id *oid) +{ + /* + * Equivalent to 'return *(unsigned int *)oid->hash;', but safe on + * platforms that don't support unaligned reads. + */ + unsigned int hash; + memcpy(&hash, oid->hash, sizeof(hash)); + return hash; +} + +/* + * 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; +}; + +/* + * 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; + const void *cmpfn_data; + + /* total number of entries (0 means the hashmap is empty) */ + unsigned int private_size; /* use hashmap_get_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; + + unsigned int do_count_items : 1; +}; + +/* hashmap functions */ + +/* + * 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. + */ +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(). + */ +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; +} + +/* + * Return the number of items in the map. + */ +static inline unsigned int hashmap_get_size(struct hashmap *map) +{ + if (map->do_count_items) + return map->private_size; + + BUG("hashmap_get_size: size not set"); + return 0; +} + +/* + * 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. + */ +void *hashmap_get(const struct hashmap *map, const void *key, + 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) +{ + 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`. + */ +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. + */ +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). + */ +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`. + */ +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); + +/* + * 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. */ +void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter); + +/* Returns the next hashmap_entry, or NULL if there are no more entries. */ +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) +{ + hashmap_iter_init(map, iter); + return hashmap_iter_next(iter); +} + +/* + * Disable item counting and automatic rehashing when adding/removing items. + * + * Normally, the hashmap keeps track of the number of items in the map + * and uses it to dynamically resize it. This (both the counting and + * the resizing) can cause problems when the map is being used by + * threaded callers (because the hashmap code does not know about the + * locking strategy used by the threaded callers and therefore, does + * not know how to protect the "private_size" counter). + */ +static inline void hashmap_disable_item_counting(struct hashmap *map) +{ + map->do_count_items = 0; +} + +/* + * Re-enable item couting when adding/removing items. + * If counting is currently disabled, it will force count them. + * It WILL NOT automatically rehash them. + */ +static inline void hashmap_enable_item_counting(struct hashmap *map) +{ + unsigned int n = 0; + struct hashmap_iter iter; + + if (map->do_count_items) + return; + + hashmap_iter_init(map, &iter); + while (hashmap_iter_next(&iter)) + n++; + + map->do_count_items = 1; + map->private_size = n; +} + +/* 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. + */ +const void *memintern(const void *data, size_t len); +static inline const char *strintern(const char *string) +{ + return memintern(string, strlen(string)); +} + +#endif |