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064af421 | 1 | /* |
63e60b86 | 2 | * Copyright (c) 2008, 2009, 2010 Nicira Networks. |
064af421 | 3 | * |
a14bc59f BP |
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: | |
064af421 | 7 | * |
a14bc59f BP |
8 | * http://www.apache.org/licenses/LICENSE-2.0 |
9 | * | |
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. | |
064af421 BP |
15 | */ |
16 | ||
17 | #include <config.h> | |
18 | #include "hmap.h" | |
19 | #include <assert.h> | |
20 | #include <stdint.h> | |
f3099647 | 21 | #include <string.h> |
064af421 | 22 | #include "coverage.h" |
f2f7be86 | 23 | #include "random.h" |
064af421 BP |
24 | #include "util.h" |
25 | ||
d76f09ea BP |
26 | COVERAGE_DEFINE(hmap_pathological); |
27 | COVERAGE_DEFINE(hmap_expand); | |
28 | COVERAGE_DEFINE(hmap_shrink); | |
29 | COVERAGE_DEFINE(hmap_reserve); | |
30 | ||
064af421 BP |
31 | /* Initializes 'hmap' as an empty hash table. */ |
32 | void | |
33 | hmap_init(struct hmap *hmap) | |
34 | { | |
35 | hmap->buckets = &hmap->one; | |
36 | hmap->one = NULL; | |
37 | hmap->mask = 0; | |
38 | hmap->n = 0; | |
39 | } | |
40 | ||
41 | /* Frees memory reserved by 'hmap'. It is the client's responsibility to free | |
42 | * the nodes themselves, if necessary. */ | |
43 | void | |
44 | hmap_destroy(struct hmap *hmap) | |
45 | { | |
46 | if (hmap && hmap->buckets != &hmap->one) { | |
47 | free(hmap->buckets); | |
48 | } | |
49 | } | |
50 | ||
f3099647 BP |
51 | /* Removes all node from 'hmap', leaving it ready to accept more nodes. Does |
52 | * not free memory allocated for 'hmap'. | |
53 | * | |
54 | * This function is appropriate when 'hmap' will soon have about as many | |
55 | * elements as it before. If 'hmap' will likely have fewer elements than | |
56 | * before, use hmap_destroy() followed by hmap_clear() to save memory and | |
57 | * iteration time. */ | |
58 | void | |
59 | hmap_clear(struct hmap *hmap) | |
60 | { | |
61 | if (hmap->n > 0) { | |
62 | hmap->n = 0; | |
63 | memset(hmap->buckets, 0, (hmap->mask + 1) * sizeof *hmap->buckets); | |
64 | } | |
65 | } | |
66 | ||
064af421 BP |
67 | /* Exchanges hash maps 'a' and 'b'. */ |
68 | void | |
69 | hmap_swap(struct hmap *a, struct hmap *b) | |
70 | { | |
71 | struct hmap tmp = *a; | |
72 | *a = *b; | |
73 | *b = tmp; | |
baa8f41b BP |
74 | hmap_moved(a); |
75 | hmap_moved(b); | |
76 | } | |
77 | ||
78 | /* Adjusts 'hmap' to compensate for having moved position in memory (e.g. due | |
79 | * to realloc()). */ | |
80 | void | |
81 | hmap_moved(struct hmap *hmap) | |
82 | { | |
83 | if (!hmap->mask) { | |
84 | hmap->buckets = &hmap->one; | |
064af421 BP |
85 | } |
86 | } | |
87 | ||
88 | static void | |
89 | resize(struct hmap *hmap, size_t new_mask) | |
90 | { | |
91 | struct hmap tmp; | |
92 | size_t i; | |
93 | ||
94 | assert(!(new_mask & (new_mask + 1))); | |
95 | assert(new_mask != SIZE_MAX); | |
96 | ||
97 | hmap_init(&tmp); | |
98 | if (new_mask) { | |
99 | tmp.buckets = xmalloc(sizeof *tmp.buckets * (new_mask + 1)); | |
100 | tmp.mask = new_mask; | |
101 | for (i = 0; i <= tmp.mask; i++) { | |
102 | tmp.buckets[i] = NULL; | |
103 | } | |
104 | } | |
105 | for (i = 0; i <= hmap->mask; i++) { | |
106 | struct hmap_node *node, *next; | |
107 | int count = 0; | |
108 | for (node = hmap->buckets[i]; node; node = next) { | |
109 | next = node->next; | |
110 | hmap_insert_fast(&tmp, node, node->hash); | |
111 | count++; | |
112 | } | |
113 | if (count > 5) { | |
114 | COVERAGE_INC(hmap_pathological); | |
115 | } | |
116 | } | |
117 | hmap_swap(hmap, &tmp); | |
118 | hmap_destroy(&tmp); | |
119 | } | |
120 | ||
121 | static size_t | |
122 | calc_mask(size_t capacity) | |
123 | { | |
124 | size_t mask = capacity / 2; | |
125 | mask |= mask >> 1; | |
126 | mask |= mask >> 2; | |
127 | mask |= mask >> 4; | |
128 | mask |= mask >> 8; | |
129 | mask |= mask >> 16; | |
130 | #if SIZE_MAX > UINT32_MAX | |
131 | mask |= mask >> 32; | |
132 | #endif | |
133 | ||
134 | /* If we need to dynamically allocate buckets we might as well allocate at | |
135 | * least 4 of them. */ | |
136 | mask |= (mask & 1) << 1; | |
137 | ||
138 | return mask; | |
139 | } | |
140 | ||
141 | /* Expands 'hmap', if necessary, to optimize the performance of searches. */ | |
142 | void | |
143 | hmap_expand(struct hmap *hmap) | |
144 | { | |
145 | size_t new_mask = calc_mask(hmap->n); | |
146 | if (new_mask > hmap->mask) { | |
147 | COVERAGE_INC(hmap_expand); | |
148 | resize(hmap, new_mask); | |
149 | } | |
150 | } | |
151 | ||
152 | /* Shrinks 'hmap', if necessary, to optimize the performance of iteration. */ | |
153 | void | |
154 | hmap_shrink(struct hmap *hmap) | |
155 | { | |
156 | size_t new_mask = calc_mask(hmap->n); | |
157 | if (new_mask < hmap->mask) { | |
158 | COVERAGE_INC(hmap_shrink); | |
159 | resize(hmap, new_mask); | |
160 | } | |
161 | } | |
162 | ||
163 | /* Expands 'hmap', if necessary, to optimize the performance of searches when | |
164 | * it has up to 'n' elements. (But iteration will be slow in a hash map whose | |
165 | * allocated capacity is much higher than its current number of nodes.) */ | |
166 | void | |
167 | hmap_reserve(struct hmap *hmap, size_t n) | |
168 | { | |
169 | size_t new_mask = calc_mask(n); | |
170 | if (new_mask > hmap->mask) { | |
171 | COVERAGE_INC(hmap_reserve); | |
172 | resize(hmap, new_mask); | |
173 | } | |
174 | } | |
63e60b86 BP |
175 | |
176 | /* Adjusts 'hmap' to compensate for 'old_node' having moved position in memory | |
177 | * to 'node' (e.g. due to realloc()). */ | |
178 | void | |
179 | hmap_node_moved(struct hmap *hmap, | |
180 | struct hmap_node *old_node, struct hmap_node *node) | |
181 | { | |
182 | struct hmap_node **bucket = &hmap->buckets[node->hash & hmap->mask]; | |
183 | while (*bucket != old_node) { | |
184 | bucket = &(*bucket)->next; | |
185 | } | |
186 | *bucket = node; | |
187 | } | |
188 | ||
f2f7be86 BP |
189 | /* Chooses and returns a randomly selected node from 'hmap', which must not be |
190 | * empty. | |
191 | * | |
192 | * I wouldn't depend on this algorithm to be fair, since I haven't analyzed it. | |
193 | * But it does at least ensure that any node in 'hmap' can be chosen. */ | |
194 | struct hmap_node * | |
195 | hmap_random_node(const struct hmap *hmap) | |
196 | { | |
197 | struct hmap_node *bucket, *node; | |
198 | size_t n, i; | |
199 | ||
200 | /* Choose a random non-empty bucket. */ | |
201 | for (i = random_uint32(); ; i++) { | |
202 | bucket = hmap->buckets[i & hmap->mask]; | |
203 | if (bucket) { | |
204 | break; | |
205 | } | |
206 | } | |
207 | ||
208 | /* Count nodes in bucket. */ | |
209 | n = 0; | |
210 | for (node = bucket; node; node = node->next) { | |
211 | n++; | |
212 | } | |
213 | ||
214 | /* Choose random node from bucket. */ | |
215 | i = random_range(n); | |
216 | for (node = bucket; i-- > 0; node = node->next) { | |
217 | continue; | |
218 | } | |
219 | return node; | |
220 | } |