1 /* xf86drmSL.c -- Skip list support
2 * Created: Mon May 10 09:28:13 1999 by faith@precisioninsight.com
3 *
4 * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
5 * All Rights Reserved.
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a
8 * copy of this software and associated documentation files (the "Software"),
9 * to deal in the Software without restriction, including without limitation
10 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
11 * and/or sell copies of the Software, and to permit persons to whom the
12 * Software is furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice (including the next
15 * paragraph) shall be included in all copies or substantial portions of the
16 * Software.
17 *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
21 * PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
22 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
23 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
24 * DEALINGS IN THE SOFTWARE.
25 *
26 * Authors: Rickard E. (Rik) Faith <faith@valinux.com>
27 *
28 * DESCRIPTION
29 *
30 * This file contains a straightforward skip list implementation.n
31 *
32 * FUTURE ENHANCEMENTS
33 *
34 * REFERENCES
35 *
36 * [Pugh90] William Pugh. Skip Lists: A Probabilistic Alternative to
37 * Balanced Trees. CACM 33(6), June 1990, pp. 668-676.
38 *
39 */
40
41 #include <stdio.h>
42 #include <stdlib.h>
43
44 #include "libdrm_macros.h"
45 #include "xf86drm.h"
46
47 #define SL_LIST_MAGIC 0xfacade00LU
48 #define SL_ENTRY_MAGIC 0x00fab1edLU
49 #define SL_FREED_MAGIC 0xdecea5edLU
50 #define SL_MAX_LEVEL 16
51 #define SL_RANDOM_SEED 0xc01055a1LU
52
53 #define SL_RANDOM_DECL static void *state = NULL
54 #define SL_RANDOM_INIT(seed) if (!state) state = drmRandomCreate(seed)
55 #define SL_RANDOM drmRandom(state)
56
57 typedef struct SLEntry {
58 unsigned long magic; /* SL_ENTRY_MAGIC */
59 unsigned long key;
60 void *value;
61 int levels;
62 struct SLEntry *forward[1]; /* variable sized array */
63 } SLEntry, *SLEntryPtr;
64
65 typedef struct SkipList {
66 unsigned long magic; /* SL_LIST_MAGIC */
67 int level;
68 int count;
69 SLEntryPtr head;
70 SLEntryPtr p0; /* Position for iteration */
71 } SkipList, *SkipListPtr;
72
SLCreateEntry(int max_level,unsigned long key,void * value)73 static SLEntryPtr SLCreateEntry(int max_level, unsigned long key, void *value)
74 {
75 SLEntryPtr entry;
76
77 if (max_level < 0 || max_level > SL_MAX_LEVEL) max_level = SL_MAX_LEVEL;
78
79 entry = drmMalloc(sizeof(*entry)
80 + (max_level + 1) * sizeof(entry->forward[0]));
81 if (!entry) return NULL;
82 entry->magic = SL_ENTRY_MAGIC;
83 entry->key = key;
84 entry->value = value;
85 entry->levels = max_level + 1;
86
87 return entry;
88 }
89
SLRandomLevel(void)90 static int SLRandomLevel(void)
91 {
92 int level = 1;
93 SL_RANDOM_DECL;
94
95 SL_RANDOM_INIT(SL_RANDOM_SEED);
96
97 while ((SL_RANDOM & 0x01) && level < SL_MAX_LEVEL) ++level;
98 return level;
99 }
100
drmSLCreate(void)101 drm_public void *drmSLCreate(void)
102 {
103 SkipListPtr list;
104 int i;
105
106 list = drmMalloc(sizeof(*list));
107 if (!list) return NULL;
108 list->magic = SL_LIST_MAGIC;
109 list->level = 0;
110 list->head = SLCreateEntry(SL_MAX_LEVEL, 0, NULL);
111 list->count = 0;
112
113 for (i = 0; i <= SL_MAX_LEVEL; i++) list->head->forward[i] = NULL;
114
115 return list;
116 }
117
drmSLDestroy(void * l)118 drm_public int drmSLDestroy(void *l)
119 {
120 SkipListPtr list = (SkipListPtr)l;
121 SLEntryPtr entry;
122 SLEntryPtr next;
123
124 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
125
126 for (entry = list->head; entry; entry = next) {
127 if (entry->magic != SL_ENTRY_MAGIC) return -1; /* Bad magic */
128 next = entry->forward[0];
129 entry->magic = SL_FREED_MAGIC;
130 drmFree(entry);
131 }
132
133 list->magic = SL_FREED_MAGIC;
134 drmFree(list);
135 return 0;
136 }
137
SLLocate(void * l,unsigned long key,SLEntryPtr * update)138 static SLEntryPtr SLLocate(void *l, unsigned long key, SLEntryPtr *update)
139 {
140 SkipListPtr list = (SkipListPtr)l;
141 SLEntryPtr entry;
142 int i;
143
144 if (list->magic != SL_LIST_MAGIC) return NULL;
145
146 for (i = list->level, entry = list->head; i >= 0; i--) {
147 while (entry->forward[i] && entry->forward[i]->key < key)
148 entry = entry->forward[i];
149 update[i] = entry;
150 }
151
152 return entry->forward[0];
153 }
154
drmSLInsert(void * l,unsigned long key,void * value)155 drm_public int drmSLInsert(void *l, unsigned long key, void *value)
156 {
157 SkipListPtr list = (SkipListPtr)l;
158 SLEntryPtr entry;
159 SLEntryPtr update[SL_MAX_LEVEL + 1];
160 int level;
161 int i;
162
163 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
164
165 entry = SLLocate(list, key, update);
166
167 if (entry && entry->key == key) return 1; /* Already in list */
168
169
170 level = SLRandomLevel();
171 if (level > list->level) {
172 level = ++list->level;
173 update[level] = list->head;
174 }
175
176 entry = SLCreateEntry(level, key, value);
177
178 /* Fix up forward pointers */
179 for (i = 0; i <= level; i++) {
180 entry->forward[i] = update[i]->forward[i];
181 update[i]->forward[i] = entry;
182 }
183
184 ++list->count;
185 return 0; /* Added to table */
186 }
187
drmSLDelete(void * l,unsigned long key)188 drm_public int drmSLDelete(void *l, unsigned long key)
189 {
190 SkipListPtr list = (SkipListPtr)l;
191 SLEntryPtr update[SL_MAX_LEVEL + 1];
192 SLEntryPtr entry;
193 int i;
194
195 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
196
197 entry = SLLocate(list, key, update);
198
199 if (!entry || entry->key != key) return 1; /* Not found */
200
201 /* Fix up forward pointers */
202 for (i = 0; i <= list->level; i++) {
203 if (update[i]->forward[i] == entry)
204 update[i]->forward[i] = entry->forward[i];
205 }
206
207 entry->magic = SL_FREED_MAGIC;
208 drmFree(entry);
209
210 while (list->level && !list->head->forward[list->level]) --list->level;
211 --list->count;
212 return 0;
213 }
214
drmSLLookup(void * l,unsigned long key,void ** value)215 drm_public int drmSLLookup(void *l, unsigned long key, void **value)
216 {
217 SkipListPtr list = (SkipListPtr)l;
218 SLEntryPtr update[SL_MAX_LEVEL + 1];
219 SLEntryPtr entry;
220
221 entry = SLLocate(list, key, update);
222
223 if (entry && entry->key == key) {
224 *value = entry;
225 return 0;
226 }
227 *value = NULL;
228 return -1;
229 }
230
drmSLLookupNeighbors(void * l,unsigned long key,unsigned long * prev_key,void ** prev_value,unsigned long * next_key,void ** next_value)231 drm_public int drmSLLookupNeighbors(void *l, unsigned long key,
232 unsigned long *prev_key, void **prev_value,
233 unsigned long *next_key, void **next_value)
234 {
235 SkipListPtr list = (SkipListPtr)l;
236 SLEntryPtr update[SL_MAX_LEVEL + 1] = {0};
237 int retcode = 0;
238
239 SLLocate(list, key, update);
240
241 *prev_key = *next_key = key;
242 *prev_value = *next_value = NULL;
243
244 if (update[0]) {
245 *prev_key = update[0]->key;
246 *prev_value = update[0]->value;
247 ++retcode;
248 if (update[0]->forward[0]) {
249 *next_key = update[0]->forward[0]->key;
250 *next_value = update[0]->forward[0]->value;
251 ++retcode;
252 }
253 }
254 return retcode;
255 }
256
drmSLNext(void * l,unsigned long * key,void ** value)257 drm_public int drmSLNext(void *l, unsigned long *key, void **value)
258 {
259 SkipListPtr list = (SkipListPtr)l;
260 SLEntryPtr entry;
261
262 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
263
264 entry = list->p0;
265
266 if (entry) {
267 list->p0 = entry->forward[0];
268 *key = entry->key;
269 *value = entry->value;
270 return 1;
271 }
272 list->p0 = NULL;
273 return 0;
274 }
275
drmSLFirst(void * l,unsigned long * key,void ** value)276 drm_public int drmSLFirst(void *l, unsigned long *key, void **value)
277 {
278 SkipListPtr list = (SkipListPtr)l;
279
280 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
281
282 list->p0 = list->head->forward[0];
283 return drmSLNext(list, key, value);
284 }
285
286 /* Dump internal data structures for debugging. */
drmSLDump(void * l)287 drm_public void drmSLDump(void *l)
288 {
289 SkipListPtr list = (SkipListPtr)l;
290 SLEntryPtr entry;
291 int i;
292
293 if (list->magic != SL_LIST_MAGIC) {
294 printf("Bad magic: 0x%08lx (expected 0x%08lx)\n",
295 list->magic, SL_LIST_MAGIC);
296 return;
297 }
298
299 printf("Level = %d, count = %d\n", list->level, list->count);
300 for (entry = list->head; entry; entry = entry->forward[0]) {
301 if (entry->magic != SL_ENTRY_MAGIC) {
302 printf("Bad magic: 0x%08lx (expected 0x%08lx)\n",
303 list->magic, SL_ENTRY_MAGIC);
304 }
305 printf("\nEntry %p <0x%08lx, %p> has %2d levels\n",
306 entry, entry->key, entry->value, entry->levels);
307 for (i = 0; i < entry->levels; i++) {
308 if (entry->forward[i]) {
309 printf(" %2d: %p <0x%08lx, %p>\n",
310 i,
311 entry->forward[i],
312 entry->forward[i]->key,
313 entry->forward[i]->value);
314 } else {
315 printf(" %2d: %p\n", i, entry->forward[i]);
316 }
317 }
318 }
319 }
320