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7b64d42d22
Interning short strings with high probability of duplicates can reduce the memory footprint and speed up comparisons. Add strintern() and memintern() APIs that use a hashmap to manage the pool of unique, interned strings. Note: strintern(getenv()) could be used to sanitize git's use of getenv(), in case we ever encounter a platform where a call to getenv() invalidates previous getenv() results (which is allowed by POSIX). Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
98 lines
2.5 KiB
C
98 lines
2.5 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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static inline unsigned int sha1hash(const unsigned char *sha1)
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{
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/*
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* Equivalent to 'return *(unsigned int *)sha1;', but safe on
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* platforms that don't support unaligned reads.
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*/
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unsigned int hash;
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memcpy(&hash, sha1, sizeof(hash));
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return hash;
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}
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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, unsigned 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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static inline void *hashmap_get_from_hash(const struct hashmap *map,
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unsigned int hash, const void *keydata)
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{
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struct hashmap_entry key;
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hashmap_entry_init(&key, hash);
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return hashmap_get(map, &key, keydata);
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}
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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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/* string interning */
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extern const void *memintern(const void *data, size_t len);
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static inline const char *strintern(const char *string)
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{
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return memintern(string, strlen(string));
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}
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#endif
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