diff options
Diffstat (limited to 'libihash/ihash.c')
| -rw-r--r-- | libihash/ihash.c | 37 |
1 files changed, 27 insertions, 10 deletions
diff --git a/libihash/ihash.c b/libihash/ihash.c index 249f4884..151c1a79 100644 --- a/libihash/ihash.c +++ b/libihash/ihash.c @@ -180,14 +180,15 @@ hurd_ihash_set_cleanup (hurd_ihash_t ht, hurd_ihash_cleanup_t cleanup, } -/* Set the maximum load factor in percent to MAX_LOAD, which should be - between 1 and 100. The default is HURD_IHASH_MAX_LOAD_DEFAULT. - New elements are only added to the hash table while the number of - hashed elements is that much percent of the total size of the hash - table. If more elements are added, the hash table is first - expanded and reorganized. A MAX_LOAD of 100 will always fill the - whole table before enlarging it, but note that this will increase - the cost of operations significantly when the table is almost full. +/* Set the maximum load factor in binary percent to MAX_LOAD, which + should be between 64 and 128. The default is + HURD_IHASH_MAX_LOAD_DEFAULT. New elements are only added to the + hash table while the number of hashed elements is that much binary + percent of the total size of the hash table. If more elements are + added, the hash table is first expanded and reorganized. A + MAX_LOAD of 128 will always fill the whole table before enlarging + it, but note that this will increase the cost of operations + significantly when the table is almost full. If the value is set to a smaller value than the current load factor, the next reorganization will happen when a new item is @@ -272,8 +273,24 @@ hurd_ihash_add (hurd_ihash_t ht, hurd_ihash_key_t key, hurd_ihash_value_t item) if (ht->size) { - /* Only fill the hash table up to its maximum load factor. */ - if ((ht->nr_items * 100) >> __builtin_ctzl (ht->size) <= ht->max_load) + /* Only fill the hash table up to its maximum load factor given + as "binary percent", where 128b% corresponds to 100%. As the + size is always a power of two, and 128 is also, the quotient + of both is also a power of two. Therefore, we can use bit + shifts to scale the number of items. + + load = nr_items * 128 / size + = nr_items * 2^{log2 (128) - log2 (size)} + = nr_items >> (log2 (size) - log2 (128)) + -- if size >= 128 + = nr_items << (log2 (128) - log2 (size)) + -- otherwise + */ + int d = __builtin_ctzl (ht->size) - 7; + unsigned int load = d >= 0 + ? ht->nr_items >> d + : ht->nr_items << -d; + if (load <= ht->max_load) if (add_one (ht, key, item)) return 0; } |