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The existing hashtable implementation (in hash.[ch]) uses open addressing (i.e. resolve hash collisions by distributing entries across the table). Thus, removal is difficult to implement with less than O(n) complexity. Resolving collisions of entries with identical hashes (e.g. via chaining) is left to the client code. Add a hashtable implementation that supports O(1) removal and is slightly easier to use due to builtin entry chaining. Supports all basic operations init, free, get, add, remove and iteration. Also includes ready-to-use hash functions based on the public domain FNV-1 algorithm (http://www.isthe.com/chongo/tech/comp/fnv). The per-entry data structure (hashmap_entry) is piggybacked in front of the client's data structure to save memory. See test-hashmap.c for usage examples. The hashtable is resized by a factor of four when 80% full. With these settings, average memory consumption is about 2/3 of hash.[ch], and insertion is about twice as fast due to less frequent resizing. Lookups are also slightly faster, because entries are strictly confined to their bucket (i.e. no data of other buckets needs to be traversed). Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
72 lines
1.8 KiB
C
72 lines
1.8 KiB
C
#ifndef HASHMAP_H
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#define HASHMAP_H
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/*
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* Generic implementation of hash-based key-value mappings.
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* See Documentation/technical/api-hashmap.txt.
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*/
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/* FNV-1 functions */
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extern unsigned int strhash(const char *buf);
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extern unsigned int strihash(const char *buf);
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extern unsigned int memhash(const void *buf, size_t len);
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extern unsigned int memihash(const void *buf, size_t len);
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/* data structures */
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struct hashmap_entry {
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struct hashmap_entry *next;
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unsigned int hash;
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};
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typedef int (*hashmap_cmp_fn)(const void *entry, const void *entry_or_key,
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const void *keydata);
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struct hashmap {
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struct hashmap_entry **table;
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hashmap_cmp_fn cmpfn;
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unsigned int size, tablesize, grow_at, shrink_at;
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};
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struct hashmap_iter {
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struct hashmap *map;
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struct hashmap_entry *next;
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unsigned int tablepos;
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};
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/* hashmap functions */
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extern void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function,
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size_t initial_size);
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extern void hashmap_free(struct hashmap *map, int free_entries);
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/* hashmap_entry functions */
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static inline void hashmap_entry_init(void *entry, int hash)
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{
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struct hashmap_entry *e = entry;
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e->hash = hash;
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e->next = NULL;
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}
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extern void *hashmap_get(const struct hashmap *map, const void *key,
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const void *keydata);
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extern void *hashmap_get_next(const struct hashmap *map, const void *entry);
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extern void hashmap_add(struct hashmap *map, void *entry);
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extern void *hashmap_put(struct hashmap *map, void *entry);
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extern void *hashmap_remove(struct hashmap *map, const void *key,
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const void *keydata);
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/* hashmap_iter functions */
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extern void hashmap_iter_init(struct hashmap *map, struct hashmap_iter *iter);
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extern void *hashmap_iter_next(struct hashmap_iter *iter);
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static inline void *hashmap_iter_first(struct hashmap *map,
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struct hashmap_iter *iter)
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{
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hashmap_iter_init(map, iter);
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return hashmap_iter_next(iter);
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}
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#endif
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