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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 | ||
0cb3b295 | 35 | q = new(Prioq, 1); |
30bdd695 LP |
36 | if (!q) |
37 | return q; | |
38 | ||
0cb3b295 YW |
39 | *q = (Prioq) { |
40 | .compare_func = compare_func, | |
41 | }; | |
42 | ||
30bdd695 LP |
43 | return q; |
44 | } | |
45 | ||
cab5b059 | 46 | Prioq* prioq_free(Prioq *q) { |
30bdd695 | 47 | if (!q) |
cab5b059 | 48 | return NULL; |
30bdd695 LP |
49 | |
50 | free(q->items); | |
6b430fdb | 51 | return mfree(q); |
30bdd695 LP |
52 | } |
53 | ||
e3017af9 LP |
54 | int prioq_ensure_allocated(Prioq **q, compare_func_t compare_func) { |
55 | assert(q); | |
56 | ||
57 | if (*q) | |
58 | return 0; | |
59 | ||
60 | *q = prioq_new(compare_func); | |
61 | if (!*q) | |
62 | return -ENOMEM; | |
63 | ||
64 | return 0; | |
65 | } | |
66 | ||
30bdd695 LP |
67 | static void swap(Prioq *q, unsigned j, unsigned k) { |
68 | void *saved_data; | |
69 | unsigned *saved_idx; | |
70 | ||
71 | assert(q); | |
72 | assert(j < q->n_items); | |
73 | assert(k < q->n_items); | |
74 | ||
75 | assert(!q->items[j].idx || *(q->items[j].idx) == j); | |
76 | assert(!q->items[k].idx || *(q->items[k].idx) == k); | |
77 | ||
78 | saved_data = q->items[j].data; | |
79 | saved_idx = q->items[j].idx; | |
80 | q->items[j].data = q->items[k].data; | |
81 | q->items[j].idx = q->items[k].idx; | |
82 | q->items[k].data = saved_data; | |
83 | q->items[k].idx = saved_idx; | |
84 | ||
85 | if (q->items[j].idx) | |
86 | *q->items[j].idx = j; | |
87 | ||
88 | if (q->items[k].idx) | |
89 | *q->items[k].idx = k; | |
90 | } | |
91 | ||
92 | static unsigned shuffle_up(Prioq *q, unsigned idx) { | |
93 | assert(q); | |
9f934223 | 94 | assert(idx < q->n_items); |
30bdd695 LP |
95 | |
96 | while (idx > 0) { | |
97 | unsigned k; | |
98 | ||
99 | k = (idx-1)/2; | |
100 | ||
8a9d23e4 | 101 | if (q->compare_func(q->items[k].data, q->items[idx].data) <= 0) |
30bdd695 LP |
102 | break; |
103 | ||
104 | swap(q, idx, k); | |
105 | idx = k; | |
106 | } | |
107 | ||
108 | return idx; | |
109 | } | |
110 | ||
111 | static unsigned shuffle_down(Prioq *q, unsigned idx) { | |
112 | assert(q); | |
113 | ||
114 | for (;;) { | |
115 | unsigned j, k, s; | |
116 | ||
117 | k = (idx+1)*2; /* right child */ | |
118 | j = k-1; /* left child */ | |
119 | ||
120 | if (j >= q->n_items) | |
121 | break; | |
122 | ||
123 | if (q->compare_func(q->items[j].data, q->items[idx].data) < 0) | |
124 | ||
125 | /* So our left child is smaller than we are, let's | |
126 | * remember this fact */ | |
127 | s = j; | |
128 | else | |
129 | s = idx; | |
130 | ||
131 | if (k < q->n_items && | |
132 | q->compare_func(q->items[k].data, q->items[s].data) < 0) | |
133 | ||
134 | /* So our right child is smaller than we are, let's | |
135 | * remember this fact */ | |
136 | s = k; | |
137 | ||
138 | /* s now points to the smallest of the three items */ | |
139 | ||
140 | if (s == idx) | |
141 | /* No swap necessary, we're done */ | |
142 | break; | |
143 | ||
144 | swap(q, idx, s); | |
145 | idx = s; | |
146 | } | |
147 | ||
148 | return idx; | |
149 | } | |
150 | ||
151 | int prioq_put(Prioq *q, void *data, unsigned *idx) { | |
152 | struct prioq_item *i; | |
153 | unsigned k; | |
154 | ||
155 | assert(q); | |
156 | ||
157 | if (q->n_items >= q->n_allocated) { | |
158 | unsigned n; | |
159 | struct prioq_item *j; | |
160 | ||
9607d947 | 161 | n = MAX((q->n_items+1) * 2, 16u); |
62d74c78 | 162 | j = reallocarray(q->items, n, sizeof(struct prioq_item)); |
30bdd695 LP |
163 | if (!j) |
164 | return -ENOMEM; | |
165 | ||
166 | q->items = j; | |
167 | q->n_allocated = n; | |
168 | } | |
169 | ||
170 | k = q->n_items++; | |
171 | i = q->items + k; | |
172 | i->data = data; | |
173 | i->idx = idx; | |
174 | ||
175 | if (idx) | |
176 | *idx = k; | |
177 | ||
178 | shuffle_up(q, k); | |
179 | ||
180 | return 0; | |
181 | } | |
182 | ||
183 | static void remove_item(Prioq *q, struct prioq_item *i) { | |
184 | struct prioq_item *l; | |
185 | ||
186 | assert(q); | |
187 | assert(i); | |
188 | ||
189 | l = q->items + q->n_items - 1; | |
190 | ||
191 | if (i == l) | |
192 | /* Last entry, let's just remove it */ | |
193 | q->n_items--; | |
194 | else { | |
195 | unsigned k; | |
196 | ||
197 | /* Not last entry, let's replace the last entry with | |
198 | * this one, and reshuffle */ | |
199 | ||
200 | k = i - q->items; | |
201 | ||
202 | i->data = l->data; | |
203 | i->idx = l->idx; | |
204 | if (i->idx) | |
205 | *i->idx = k; | |
206 | q->n_items--; | |
207 | ||
208 | k = shuffle_down(q, k); | |
209 | shuffle_up(q, k); | |
210 | } | |
211 | } | |
212 | ||
44a6b1b6 | 213 | _pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) { |
30bdd695 LP |
214 | struct prioq_item *i; |
215 | ||
216 | assert(q); | |
217 | ||
cd86deef YW |
218 | if (q->n_items <= 0) |
219 | return NULL; | |
220 | ||
30bdd695 | 221 | if (idx) { |
c2ba3ad6 | 222 | if (*idx == PRIOQ_IDX_NULL || |
e6e637a1 | 223 | *idx >= q->n_items) |
e3017af9 LP |
224 | return NULL; |
225 | ||
30bdd695 | 226 | i = q->items + *idx; |
e3017af9 LP |
227 | if (i->data != data) |
228 | return NULL; | |
30bdd695 LP |
229 | |
230 | return i; | |
231 | } else { | |
232 | for (i = q->items; i < q->items + q->n_items; i++) | |
233 | if (i->data == data) | |
234 | return i; | |
235 | return NULL; | |
236 | } | |
237 | } | |
238 | ||
239 | int prioq_remove(Prioq *q, void *data, unsigned *idx) { | |
240 | struct prioq_item *i; | |
241 | ||
a3de5ae1 LP |
242 | if (!q) |
243 | return 0; | |
30bdd695 LP |
244 | |
245 | i = find_item(q, data, idx); | |
246 | if (!i) | |
247 | return 0; | |
248 | ||
249 | remove_item(q, i); | |
250 | return 1; | |
251 | } | |
252 | ||
253 | int prioq_reshuffle(Prioq *q, void *data, unsigned *idx) { | |
254 | struct prioq_item *i; | |
255 | unsigned k; | |
256 | ||
257 | assert(q); | |
258 | ||
259 | i = find_item(q, data, idx); | |
260 | if (!i) | |
261 | return 0; | |
262 | ||
263 | k = i - q->items; | |
264 | k = shuffle_down(q, k); | |
265 | shuffle_up(q, k); | |
266 | return 1; | |
267 | } | |
268 | ||
269 | void *prioq_peek(Prioq *q) { | |
a3de5ae1 LP |
270 | |
271 | if (!q) | |
272 | return NULL; | |
30bdd695 LP |
273 | |
274 | if (q->n_items <= 0) | |
275 | return NULL; | |
276 | ||
277 | return q->items[0].data; | |
278 | } | |
279 | ||
280 | void *prioq_pop(Prioq *q) { | |
281 | void *data; | |
282 | ||
a3de5ae1 LP |
283 | if (!q) |
284 | return NULL; | |
30bdd695 LP |
285 | |
286 | if (q->n_items <= 0) | |
287 | return NULL; | |
288 | ||
289 | data = q->items[0].data; | |
290 | remove_item(q, q->items); | |
291 | return data; | |
292 | } | |
293 | ||
294 | unsigned prioq_size(Prioq *q) { | |
a3de5ae1 LP |
295 | |
296 | if (!q) | |
297 | return 0; | |
30bdd695 LP |
298 | |
299 | return q->n_items; | |
30bdd695 | 300 | } |
718db961 | 301 | |
30bdd695 | 302 | bool prioq_isempty(Prioq *q) { |
a3de5ae1 LP |
303 | |
304 | if (!q) | |
305 | return true; | |
30bdd695 LP |
306 | |
307 | return q->n_items <= 0; | |
308 | } |