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53e1b683 | 1 | /* SPDX-License-Identifier: LGPL-2.1+ */ |
30bdd695 | 2 | |
f36f8f78 DH |
3 | /* |
4 | * Priority Queue | |
5 | * The prioq object implements a priority queue. That is, it orders objects by | |
6 | * their priority and allows O(1) access to the object with the highest | |
7 | * priority. Insertion and removal are Θ(log n). Optionally, the caller can | |
8 | * provide a pointer to an index which will be kept up-to-date by the prioq. | |
9 | * | |
10 | * The underlying algorithm used in this implementation is a Heap. | |
11 | */ | |
12 | ||
11c3a366 TA |
13 | #include <errno.h> |
14 | #include <stdlib.h> | |
15 | ||
b5efdb8a | 16 | #include "alloc-util.h" |
11c3a366 | 17 | #include "hashmap.h" |
93cc7779 | 18 | #include "prioq.h" |
30bdd695 LP |
19 | |
20 | struct prioq_item { | |
21 | void *data; | |
22 | unsigned *idx; | |
23 | }; | |
24 | ||
25 | struct Prioq { | |
26 | compare_func_t compare_func; | |
27 | unsigned n_items, n_allocated; | |
28 | ||
29 | struct prioq_item *items; | |
30 | }; | |
31 | ||
32 | Prioq *prioq_new(compare_func_t compare_func) { | |
33 | Prioq *q; | |
34 | ||
35 | q = new0(Prioq, 1); | |
36 | if (!q) | |
37 | return q; | |
38 | ||
39 | q->compare_func = compare_func; | |
40 | return q; | |
41 | } | |
42 | ||
cab5b059 | 43 | Prioq* prioq_free(Prioq *q) { |
30bdd695 | 44 | if (!q) |
cab5b059 | 45 | return NULL; |
30bdd695 LP |
46 | |
47 | free(q->items); | |
6b430fdb | 48 | return mfree(q); |
30bdd695 LP |
49 | } |
50 | ||
e3017af9 LP |
51 | int prioq_ensure_allocated(Prioq **q, compare_func_t compare_func) { |
52 | assert(q); | |
53 | ||
54 | if (*q) | |
55 | return 0; | |
56 | ||
57 | *q = prioq_new(compare_func); | |
58 | if (!*q) | |
59 | return -ENOMEM; | |
60 | ||
61 | return 0; | |
62 | } | |
63 | ||
30bdd695 LP |
64 | static void swap(Prioq *q, unsigned j, unsigned k) { |
65 | void *saved_data; | |
66 | unsigned *saved_idx; | |
67 | ||
68 | assert(q); | |
69 | assert(j < q->n_items); | |
70 | assert(k < q->n_items); | |
71 | ||
72 | assert(!q->items[j].idx || *(q->items[j].idx) == j); | |
73 | assert(!q->items[k].idx || *(q->items[k].idx) == k); | |
74 | ||
75 | saved_data = q->items[j].data; | |
76 | saved_idx = q->items[j].idx; | |
77 | q->items[j].data = q->items[k].data; | |
78 | q->items[j].idx = q->items[k].idx; | |
79 | q->items[k].data = saved_data; | |
80 | q->items[k].idx = saved_idx; | |
81 | ||
82 | if (q->items[j].idx) | |
83 | *q->items[j].idx = j; | |
84 | ||
85 | if (q->items[k].idx) | |
86 | *q->items[k].idx = k; | |
87 | } | |
88 | ||
89 | static unsigned shuffle_up(Prioq *q, unsigned idx) { | |
90 | assert(q); | |
9f934223 | 91 | assert(idx < q->n_items); |
30bdd695 LP |
92 | |
93 | while (idx > 0) { | |
94 | unsigned k; | |
95 | ||
96 | k = (idx-1)/2; | |
97 | ||
8a9d23e4 | 98 | if (q->compare_func(q->items[k].data, q->items[idx].data) <= 0) |
30bdd695 LP |
99 | break; |
100 | ||
101 | swap(q, idx, k); | |
102 | idx = k; | |
103 | } | |
104 | ||
105 | return idx; | |
106 | } | |
107 | ||
108 | static unsigned shuffle_down(Prioq *q, unsigned idx) { | |
109 | assert(q); | |
110 | ||
111 | for (;;) { | |
112 | unsigned j, k, s; | |
113 | ||
114 | k = (idx+1)*2; /* right child */ | |
115 | j = k-1; /* left child */ | |
116 | ||
117 | if (j >= q->n_items) | |
118 | break; | |
119 | ||
120 | if (q->compare_func(q->items[j].data, q->items[idx].data) < 0) | |
121 | ||
122 | /* So our left child is smaller than we are, let's | |
123 | * remember this fact */ | |
124 | s = j; | |
125 | else | |
126 | s = idx; | |
127 | ||
128 | if (k < q->n_items && | |
129 | q->compare_func(q->items[k].data, q->items[s].data) < 0) | |
130 | ||
131 | /* So our right child is smaller than we are, let's | |
132 | * remember this fact */ | |
133 | s = k; | |
134 | ||
135 | /* s now points to the smallest of the three items */ | |
136 | ||
137 | if (s == idx) | |
138 | /* No swap necessary, we're done */ | |
139 | break; | |
140 | ||
141 | swap(q, idx, s); | |
142 | idx = s; | |
143 | } | |
144 | ||
145 | return idx; | |
146 | } | |
147 | ||
148 | int prioq_put(Prioq *q, void *data, unsigned *idx) { | |
149 | struct prioq_item *i; | |
150 | unsigned k; | |
151 | ||
152 | assert(q); | |
153 | ||
154 | if (q->n_items >= q->n_allocated) { | |
155 | unsigned n; | |
156 | struct prioq_item *j; | |
157 | ||
9607d947 | 158 | n = MAX((q->n_items+1) * 2, 16u); |
62d74c78 | 159 | j = reallocarray(q->items, n, sizeof(struct prioq_item)); |
30bdd695 LP |
160 | if (!j) |
161 | return -ENOMEM; | |
162 | ||
163 | q->items = j; | |
164 | q->n_allocated = n; | |
165 | } | |
166 | ||
167 | k = q->n_items++; | |
168 | i = q->items + k; | |
169 | i->data = data; | |
170 | i->idx = idx; | |
171 | ||
172 | if (idx) | |
173 | *idx = k; | |
174 | ||
175 | shuffle_up(q, k); | |
176 | ||
177 | return 0; | |
178 | } | |
179 | ||
180 | static void remove_item(Prioq *q, struct prioq_item *i) { | |
181 | struct prioq_item *l; | |
182 | ||
183 | assert(q); | |
184 | assert(i); | |
185 | ||
186 | l = q->items + q->n_items - 1; | |
187 | ||
188 | if (i == l) | |
189 | /* Last entry, let's just remove it */ | |
190 | q->n_items--; | |
191 | else { | |
192 | unsigned k; | |
193 | ||
194 | /* Not last entry, let's replace the last entry with | |
195 | * this one, and reshuffle */ | |
196 | ||
197 | k = i - q->items; | |
198 | ||
199 | i->data = l->data; | |
200 | i->idx = l->idx; | |
201 | if (i->idx) | |
202 | *i->idx = k; | |
203 | q->n_items--; | |
204 | ||
205 | k = shuffle_down(q, k); | |
206 | shuffle_up(q, k); | |
207 | } | |
208 | } | |
209 | ||
44a6b1b6 | 210 | _pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) { |
30bdd695 LP |
211 | struct prioq_item *i; |
212 | ||
213 | assert(q); | |
214 | ||
cd86deef YW |
215 | if (q->n_items <= 0) |
216 | return NULL; | |
217 | ||
30bdd695 | 218 | if (idx) { |
c2ba3ad6 LP |
219 | if (*idx == PRIOQ_IDX_NULL || |
220 | *idx > q->n_items) | |
e3017af9 LP |
221 | return NULL; |
222 | ||
30bdd695 | 223 | i = q->items + *idx; |
e3017af9 LP |
224 | if (i->data != data) |
225 | return NULL; | |
30bdd695 LP |
226 | |
227 | return i; | |
228 | } else { | |
229 | for (i = q->items; i < q->items + q->n_items; i++) | |
230 | if (i->data == data) | |
231 | return i; | |
232 | return NULL; | |
233 | } | |
234 | } | |
235 | ||
236 | int prioq_remove(Prioq *q, void *data, unsigned *idx) { | |
237 | struct prioq_item *i; | |
238 | ||
a3de5ae1 LP |
239 | if (!q) |
240 | return 0; | |
30bdd695 LP |
241 | |
242 | i = find_item(q, data, idx); | |
243 | if (!i) | |
244 | return 0; | |
245 | ||
246 | remove_item(q, i); | |
247 | return 1; | |
248 | } | |
249 | ||
250 | int prioq_reshuffle(Prioq *q, void *data, unsigned *idx) { | |
251 | struct prioq_item *i; | |
252 | unsigned k; | |
253 | ||
254 | assert(q); | |
255 | ||
256 | i = find_item(q, data, idx); | |
257 | if (!i) | |
258 | return 0; | |
259 | ||
260 | k = i - q->items; | |
261 | k = shuffle_down(q, k); | |
262 | shuffle_up(q, k); | |
263 | return 1; | |
264 | } | |
265 | ||
266 | void *prioq_peek(Prioq *q) { | |
a3de5ae1 LP |
267 | |
268 | if (!q) | |
269 | return NULL; | |
30bdd695 LP |
270 | |
271 | if (q->n_items <= 0) | |
272 | return NULL; | |
273 | ||
274 | return q->items[0].data; | |
275 | } | |
276 | ||
277 | void *prioq_pop(Prioq *q) { | |
278 | void *data; | |
279 | ||
a3de5ae1 LP |
280 | if (!q) |
281 | return NULL; | |
30bdd695 LP |
282 | |
283 | if (q->n_items <= 0) | |
284 | return NULL; | |
285 | ||
286 | data = q->items[0].data; | |
287 | remove_item(q, q->items); | |
288 | return data; | |
289 | } | |
290 | ||
291 | unsigned prioq_size(Prioq *q) { | |
a3de5ae1 LP |
292 | |
293 | if (!q) | |
294 | return 0; | |
30bdd695 LP |
295 | |
296 | return q->n_items; | |
30bdd695 | 297 | } |
718db961 | 298 | |
30bdd695 | 299 | bool prioq_isempty(Prioq *q) { |
a3de5ae1 LP |
300 | |
301 | if (!q) | |
302 | return true; | |
30bdd695 LP |
303 | |
304 | return q->n_items <= 0; | |
305 | } |