The same rationale applies here as for the hash table. Power of two size should give better performance, and using the algorithm hash = sh + i/2 + i*i/2 should result in only distinct hash values when hitting collisions. Should give a performance increase as we can do bitmasking instead of a modulo operation for fitting the hash in the address space. --- src/util/set.c | 103 ++++++++++++++++++++++++++++++--------------------------- src/util/set.h | 1 - 2 files changed, 54 insertions(+), 50 deletions(-)
diff --git a/src/util/set.c b/src/util/set.c index f01f869..8f0ad0d 100644 --- a/src/util/set.c +++ b/src/util/set.c @@ -48,40 +48,46 @@ uint32_t deleted_key_value; const void *deleted_key = &deleted_key_value; +/** + * We chose table sizes that's a power of two. + * This is computationally less expensive than primes. + * FNV-1a has good avalanche properties, so collision is not an issue. + * These tables are sized to have an extra 10% free to avoid + * exponential performance degradation as the hash table fills + */ static const struct { - uint32_t max_entries, size, rehash; + uint32_t max_entries, size; } hash_sizes[] = { - { 2, 5, 3 }, - { 4, 7, 5 }, - { 8, 13, 11 }, - { 16, 19, 17 }, - { 32, 43, 41 }, - { 64, 73, 71 }, - { 128, 151, 149 }, - { 256, 283, 281 }, - { 512, 571, 569 }, - { 1024, 1153, 1151 }, - { 2048, 2269, 2267 }, - { 4096, 4519, 4517 }, - { 8192, 9013, 9011 }, - { 16384, 18043, 18041 }, - { 32768, 36109, 36107 }, - { 65536, 72091, 72089 }, - { 131072, 144409, 144407 }, - { 262144, 288361, 288359 }, - { 524288, 576883, 576881 }, - { 1048576, 1153459, 1153457 }, - { 2097152, 2307163, 2307161 }, - { 4194304, 4613893, 4613891 }, - { 8388608, 9227641, 9227639 }, - { 16777216, 18455029, 18455027 }, - { 33554432, 36911011, 36911009 }, - { 67108864, 73819861, 73819859 }, - { 134217728, 147639589, 147639587 }, - { 268435456, 295279081, 295279079 }, - { 536870912, 590559793, 590559791 }, - { 1073741824, 1181116273, 1181116271 }, - { 2147483648ul, 2362232233ul, 2362232231ul } + { 3, 4 }, + { 7, 8 }, + { 14, 16 }, + { 28, 32 }, + { 57, 64 }, + { 115, 128 }, + { 230, 256 }, + { 460, 512 }, + { 921, 1024 }, + { 1843, 2048 }, + { 3686, 4096 }, + { 7372, 8192 }, + { 14745, 16384 }, + { 29491, 32768 }, + { 58982, 65536 }, + { 117964, 131072 }, + { 235929, 262144 }, + { 471859, 524288 }, + { 943718, 1048576 }, + { 1887436, 2097152 }, + { 3774873, 4194304 }, + { 7549747, 8388608 }, + { 15099494, 16777216 }, + { 30198988, 33554432 }, + { 60397977, 67108864 }, + { 120795955, 134217728 }, + { 241591910, 268435456 }, + { 483183820, 536870912 }, + { 966367641, 1073741824 }, + { 1932735283ul, 2147483648ul } }; static int @@ -116,7 +122,6 @@ _mesa_set_create(void *mem_ctx, ht->size_index = 0; ht->size = hash_sizes[ht->size_index].size; - ht->rehash = hash_sizes[ht->size_index].rehash; ht->max_entries = hash_sizes[ht->size_index].max_entries; ht->key_hash_function = key_hash_function; ht->key_equals_function = key_equals_function; @@ -163,12 +168,12 @@ _mesa_set_destroy(struct set *ht, void (*delete_function)(struct set_entry *entr static struct set_entry * set_search(const struct set *ht, uint32_t hash, const void *key) { - uint32_t hash_address; + uint32_t start_hash_address = hash & (ht->size - 1); + uint32_t hash_address = start_hash_address; + // Start at 2, or we will match start_hash_address initially and bail + uint32_t quad_hash = 2; - hash_address = hash % ht->size; do { - uint32_t double_hash; - struct set_entry *entry = ht->table + hash_address; if (entry_is_free(entry)) { @@ -179,10 +184,10 @@ set_search(const struct set *ht, uint32_t hash, const void *key) } } - double_hash = 1 + hash % ht->rehash; - - hash_address = (hash_address + double_hash) % ht->size; - } while (hash_address != hash % ht->size); + hash_address = (start_hash_address + (quad_hash / 2) + + ((quad_hash * quad_hash) / 2)) & (ht->size - 1); + quad_hash++; + } while (hash_address != start_hash_address); return NULL; } @@ -225,7 +230,6 @@ set_rehash(struct set *ht, unsigned new_size_index) ht->table = table; ht->size_index = new_size_index; ht->size = hash_sizes[ht->size_index].size; - ht->rehash = hash_sizes[ht->size_index].rehash; ht->max_entries = hash_sizes[ht->size_index].max_entries; ht->entries = 0; ht->deleted_entries = 0; @@ -250,7 +254,9 @@ set_rehash(struct set *ht, unsigned new_size_index) static struct set_entry * set_add(struct set *ht, uint32_t hash, const void *key) { - uint32_t hash_address; + uint32_t start_hash_address = hash & (ht->size - 1); + uint32_t hash_address = start_hash_address; + uint32_t quad_hash = 2; struct set_entry *available_entry = NULL; if (ht->entries >= ht->max_entries) { @@ -259,10 +265,8 @@ set_add(struct set *ht, uint32_t hash, const void *key) set_rehash(ht, ht->size_index); } - hash_address = hash % ht->size; do { struct set_entry *entry = ht->table + hash_address; - uint32_t double_hash; if (!entry_is_present(entry)) { /* Stash the first available entry we find */ @@ -288,10 +292,11 @@ set_add(struct set *ht, uint32_t hash, const void *key) return entry; } - double_hash = 1 + hash % ht->rehash; + hash_address = (start_hash_address + (quad_hash / 2) + + ((quad_hash * quad_hash) / 2)) & (ht->size - 1); + quad_hash++; + } while (hash_address != start_hash_address); - hash_address = (hash_address + double_hash) % ht->size; - } while (hash_address != hash % ht->size); if (available_entry) { if (entry_is_deleted(available_entry)) @@ -368,7 +373,7 @@ _mesa_set_random_entry(struct set *ht, int (*predicate)(struct set_entry *entry)) { struct set_entry *entry; - uint32_t i = rand() % ht->size; + uint32_t i = rand() & (ht->size - 1); if (ht->entries == 0) return NULL; diff --git a/src/util/set.h b/src/util/set.h index 9acd2c2..5a1097c 100644 --- a/src/util/set.h +++ b/src/util/set.h @@ -46,7 +46,6 @@ struct set { uint32_t (*key_hash_function)(const void *key); bool (*key_equals_function)(const void *a, const void *b); uint32_t size; - uint32_t rehash; uint32_t max_entries; uint32_t size_index; uint32_t entries; -- 2.2.1 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev