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c73592812d
This avoids unnecessary re-allocations and reinsertions. On webkit.git (i.e. about 182k inserts to the name hash table), this reduces about 100ms out of 3s user time. Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
50 lines
1.4 KiB
C
50 lines
1.4 KiB
C
#ifndef HASH_H
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#define HASH_H
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/*
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* These are some simple generic hash table helper functions.
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* Not necessarily suitable for all users, but good for things
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* where you want to just keep track of a list of things, and
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* have a good hash to use on them.
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*
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* It keeps the hash table at roughly 50-75% free, so the memory
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* cost of the hash table itself is roughly
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*
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* 3 * 2*sizeof(void *) * nr_of_objects
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*
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* bytes.
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*
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* FIXME: on 64-bit architectures, we waste memory. It would be
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* good to have just 32-bit pointers, requiring a special allocator
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* for hashed entries or something.
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*/
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struct hash_table_entry {
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unsigned int hash;
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void *ptr;
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};
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struct hash_table {
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unsigned int size, nr;
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struct hash_table_entry *array;
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};
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extern void *lookup_hash(unsigned int hash, const struct hash_table *table);
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extern void **insert_hash(unsigned int hash, void *ptr, struct hash_table *table);
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extern int for_each_hash(const struct hash_table *table, int (*fn)(void *, void *), void *data);
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extern void free_hash(struct hash_table *table);
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static inline void init_hash(struct hash_table *table)
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{
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table->size = 0;
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table->nr = 0;
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table->array = NULL;
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}
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static inline void preallocate_hash(struct hash_table *table, unsigned int elts)
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{
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assert(table->size == 0 && table->nr == 0 && table->array == NULL);
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table->size = elts * 2;
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table->array = xcalloc(sizeof(struct hash_table_entry), table->size);
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}
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#endif
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