2 * Copyright (c) 2013 Nicira, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at:
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
21 static bool hindex_node_is_body(const struct hindex_node *);
22 static bool hindex_node_is_head(const struct hindex_node *);
23 static void hindex_resize(struct hindex *, size_t new_mask);
24 static size_t hindex_calc_mask(size_t capacity);
26 COVERAGE_DEFINE(hindex_pathological);
27 COVERAGE_DEFINE(hindex_expand);
28 COVERAGE_DEFINE(hindex_shrink);
29 COVERAGE_DEFINE(hindex_reserve);
31 /* Initializes 'hindex' as an empty hash index. */
33 hindex_init(struct hindex *hindex)
35 hindex->buckets = &hindex->one;
41 /* Frees memory reserved by 'hindex'. It is the client's responsibility to
42 * free the nodes themselves, if necessary. */
44 hindex_destroy(struct hindex *hindex)
46 if (hindex && hindex->buckets != &hindex->one) {
47 free(hindex->buckets);
51 /* Removes all node from 'hindex', leaving it ready to accept more nodes. Does
52 * not free memory allocated for 'hindex'.
54 * This function is appropriate when 'hindex' will soon have about as many
55 * elements as it before. If 'hindex' will likely have fewer elements than
56 * before, use hindex_destroy() followed by hindex_clear() to save memory and
59 hindex_clear(struct hindex *hindex)
61 if (hindex->n_unique > 0) {
63 memset(hindex->buckets, 0,
64 (hindex->mask + 1) * sizeof *hindex->buckets);
68 /* Exchanges hash indexes 'a' and 'b'. */
70 hindex_swap(struct hindex *a, struct hindex *b)
72 struct hindex tmp = *a;
79 /* Adjusts 'hindex' to compensate for having moved position in memory (e.g. due
82 hindex_moved(struct hindex *hindex)
85 hindex->buckets = &hindex->one;
89 /* Expands 'hindex', if necessary, to optimize the performance of searches. */
91 hindex_expand(struct hindex *hindex)
93 size_t new_mask = hindex_calc_mask(hindex->n_unique);
94 if (new_mask > hindex->mask) {
95 COVERAGE_INC(hindex_expand);
96 hindex_resize(hindex, new_mask);
100 /* Shrinks 'hindex', if necessary, to optimize the performance of iteration. */
102 hindex_shrink(struct hindex *hindex)
104 size_t new_mask = hindex_calc_mask(hindex->n_unique);
105 if (new_mask < hindex->mask) {
106 COVERAGE_INC(hindex_shrink);
107 hindex_resize(hindex, new_mask);
111 /* Expands 'hindex', if necessary, to optimize the performance of searches when
112 * it has up to 'n' unique hashes. (But iteration will be slow in a hash index
113 * whose allocated capacity is much higher than its current number of
116 hindex_reserve(struct hindex *hindex, size_t n)
118 size_t new_mask = hindex_calc_mask(n);
119 if (new_mask > hindex->mask) {
120 COVERAGE_INC(hindex_reserve);
121 hindex_resize(hindex, new_mask);
125 /* Inserts 'node', with the given 'hash', into 'hindex'. Never automatically
126 * expands 'hindex' (use hindex_insert() instead if you want that). */
128 hindex_insert_fast(struct hindex *hindex,
129 struct hindex_node *node, size_t hash)
131 struct hindex_node *head = hindex_node_with_hash(hindex, hash);
133 /* 'head' is an existing head with hash == 'hash'.
134 * Insert 'node' as a body node just below 'head'. */
142 /* No existing node has hash 'hash'. Insert 'node' as a new head in
144 struct hindex_node **bucket = &hindex->buckets[hash & hindex->mask];
153 /* Inserts 'node', with the given 'hash', into 'hindex', and expands 'hindex'
154 * if necessary to optimize search performance. */
156 hindex_insert(struct hindex *hindex, struct hindex_node *node, size_t hash)
158 hindex_insert_fast(hindex, node, hash);
159 if (hindex->n_unique / 2 > hindex->mask) {
160 hindex_expand(hindex);
164 /* Removes 'node' from 'hindex'. Does not shrink the hash index; call
165 * hindex_shrink() directly if desired. */
167 hindex_remove(struct hindex *hindex, struct hindex_node *node)
169 if (!hindex_node_is_head(node)) {
170 node->d->s = node->s;
172 node->s->d = node->d;
175 struct hindex_node **head;
177 for (head = &hindex->buckets[node->hash & hindex->mask];
178 (*head)->hash != node->hash;
186 node->s->d = node->d;
194 /* Helper functions. */
196 /* Returns true if 'node', which must be inserted into an hindex, is a "body"
197 * node, that is, it is not reachable from a bucket by following zero or more
198 * 'd' pointers. Returns false otherwise. */
200 hindex_node_is_body(const struct hindex_node *node)
202 return node->d && node->d->hash == node->hash;
205 /* Returns true if 'node', which must be inserted into an hindex, is a "head"
206 * node, that is, if it is reachable from a bucket by following zero or more
207 * 'd' pointers. Returns false if 'node' is a body node (and therefore one
208 * must follow at least one 's' pointer to reach it). */
210 hindex_node_is_head(const struct hindex_node *node)
212 return !hindex_node_is_body(node);
215 /* Reallocates 'hindex''s array of buckets to use bitwise mask 'new_mask'. */
217 hindex_resize(struct hindex *hindex, size_t new_mask)
222 ovs_assert(is_pow2(new_mask + 1));
223 ovs_assert(new_mask != SIZE_MAX);
227 tmp.buckets = xmalloc(sizeof *tmp.buckets * (new_mask + 1));
229 for (i = 0; i <= tmp.mask; i++) {
230 tmp.buckets[i] = NULL;
233 for (i = 0; i <= hindex->mask; i++) {
234 struct hindex_node *node, *next;
238 for (node = hindex->buckets[i]; node; node = next) {
239 struct hindex_node **head = &tmp.buckets[node->hash & tmp.mask];
247 COVERAGE_INC(hindex_pathological);
250 tmp.n_unique = hindex->n_unique;
251 hindex_swap(hindex, &tmp);
252 hindex_destroy(&tmp);
255 /* Returns the bitwise mask to use in struct hindex to support 'capacity'
256 * hindex_nodes with unique hashes. */
258 hindex_calc_mask(size_t capacity)
260 size_t mask = capacity / 2;
266 #if SIZE_MAX > UINT32_MAX
270 /* If we need to dynamically allocate buckets we might as well allocate at
271 * least 4 of them. */
272 mask |= (mask & 1) << 1;
277 /* Returns the head node in 'hindex' with the given 'hash', or a null pointer
278 * if no nodes have that hash value. */
280 hindex_node_with_hash(const struct hindex *hindex, size_t hash)
282 struct hindex_node *node = hindex->buckets[hash & hindex->mask];
284 while (node && node->hash != hash) {
290 /* Returns the head node in 'hindex' with the given 'hash'. 'hindex' must
291 * contain a head node with the given hash. */
292 static struct hindex_node *
293 hindex_head_node(const struct hindex *hindex, size_t hash)
295 struct hindex_node *node = hindex->buckets[hash & hindex->mask];
297 while (node->hash != hash) {
303 static struct hindex_node *
304 hindex_next__(const struct hindex *hindex, size_t start)
307 for (i = start; i <= hindex->mask; i++) {
308 struct hindex_node *node = hindex->buckets[i];
316 /* Returns the first node in 'hindex', in arbitrary order, or a null pointer if
317 * 'hindex' is empty. */
319 hindex_first(const struct hindex *hindex)
321 return hindex_next__(hindex, 0);
324 /* Returns the next node in 'hindex' following 'node', in arbitrary order, or a
325 * null pointer if 'node' is the last node in 'hindex'.
327 * If the hash index has been reallocated since 'node' was visited, some nodes
328 * may be skipped or visited twice. */
330 hindex_next(const struct hindex *hindex, const struct hindex_node *node)
332 struct hindex_node *head;
334 /* If there's a node with the same hash, return it. */
339 /* If there's another node in the same bucket, return it. */
340 head = hindex_head_node(hindex, node->hash);
345 /* Return the first node in the next (or later) bucket. */
346 return hindex_next__(hindex, (node->hash & hindex->mask) + 1);