1 /* xf86drmSL.c -- Skip list support
2 * Created: Mon May 10 09:28:13 1999 by faith@precisioninsight.com
4 * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
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12 * Software is furnished to do so, subject to the following conditions:
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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
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24 * DEALINGS IN THE SOFTWARE.
26 * Authors: Rickard E. (Rik) Faith <faith@valinux.com>
30 * This file contains a straightforward skip list implementation.n
36 * [Pugh90] William Pugh. Skip Lists: A Probabilistic Alternative to
37 * Balanced Trees. CACM 33(6), June 1990, pp. 668-676.
46 #define SL_LIST_MAGIC 0xfacade00LU
47 #define SL_ENTRY_MAGIC 0x00fab1edLU
48 #define SL_FREED_MAGIC 0xdecea5edLU
49 #define SL_MAX_LEVEL 16
50 #define SL_RANDOM_SEED 0xc01055a1LU
52 #define SL_RANDOM_DECL static void *state = NULL
53 #define SL_RANDOM_INIT(seed) if (!state) state = drmRandomCreate(seed)
54 #define SL_RANDOM drmRandom(state)
56 typedef struct SLEntry {
57 unsigned long magic; /* SL_ENTRY_MAGIC */
61 struct SLEntry *forward[1]; /* variable sized array */
62 } SLEntry, *SLEntryPtr;
64 typedef struct SkipList {
65 unsigned long magic; /* SL_LIST_MAGIC */
69 SLEntryPtr p0; /* Position for iteration */
70 } SkipList, *SkipListPtr;
72 static SLEntryPtr SLCreateEntry(int max_level, unsigned long key, void *value)
76 if (max_level < 0 || max_level > SL_MAX_LEVEL) max_level = SL_MAX_LEVEL;
78 entry = drmMalloc(sizeof(*entry)
79 + (max_level + 1) * sizeof(entry->forward[0]));
80 if (!entry) return NULL;
81 entry->magic = SL_ENTRY_MAGIC;
84 entry->levels = max_level + 1;
89 static int SLRandomLevel(void)
94 SL_RANDOM_INIT(SL_RANDOM_SEED);
96 while ((SL_RANDOM & 0x01) && level < SL_MAX_LEVEL) ++level;
100 void *drmSLCreate(void)
105 list = drmMalloc(sizeof(*list));
106 if (!list) return NULL;
107 list->magic = SL_LIST_MAGIC;
109 list->head = SLCreateEntry(SL_MAX_LEVEL, 0, NULL);
112 for (i = 0; i <= SL_MAX_LEVEL; i++) list->head->forward[i] = NULL;
117 int drmSLDestroy(void *l)
119 SkipListPtr list = (SkipListPtr)l;
123 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
125 for (entry = list->head; entry; entry = next) {
126 if (entry->magic != SL_ENTRY_MAGIC) return -1; /* Bad magic */
127 next = entry->forward[0];
128 entry->magic = SL_FREED_MAGIC;
132 list->magic = SL_FREED_MAGIC;
137 static SLEntryPtr SLLocate(void *l, unsigned long key, SLEntryPtr *update)
139 SkipListPtr list = (SkipListPtr)l;
143 if (list->magic != SL_LIST_MAGIC) return NULL;
145 for (i = list->level, entry = list->head; i >= 0; i--) {
146 while (entry->forward[i] && entry->forward[i]->key < key)
147 entry = entry->forward[i];
151 return entry->forward[0];
154 int drmSLInsert(void *l, unsigned long key, void *value)
156 SkipListPtr list = (SkipListPtr)l;
158 SLEntryPtr update[SL_MAX_LEVEL + 1];
162 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
164 entry = SLLocate(list, key, update);
166 if (entry && entry->key == key) return 1; /* Already in list */
169 level = SLRandomLevel();
170 if (level > list->level) {
171 level = ++list->level;
172 update[level] = list->head;
175 entry = SLCreateEntry(level, key, value);
177 /* Fix up forward pointers */
178 for (i = 0; i <= level; i++) {
179 entry->forward[i] = update[i]->forward[i];
180 update[i]->forward[i] = entry;
184 return 0; /* Added to table */
187 int drmSLDelete(void *l, unsigned long key)
189 SkipListPtr list = (SkipListPtr)l;
190 SLEntryPtr update[SL_MAX_LEVEL + 1];
194 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
196 entry = SLLocate(list, key, update);
198 if (!entry || entry->key != key) return 1; /* Not found */
200 /* Fix up forward pointers */
201 for (i = 0; i <= list->level; i++) {
202 if (update[i]->forward[i] == entry)
203 update[i]->forward[i] = entry->forward[i];
206 entry->magic = SL_FREED_MAGIC;
209 while (list->level && !list->head->forward[list->level]) --list->level;
214 int drmSLLookup(void *l, unsigned long key, void **value)
216 SkipListPtr list = (SkipListPtr)l;
217 SLEntryPtr update[SL_MAX_LEVEL + 1];
220 entry = SLLocate(list, key, update);
222 if (entry && entry->key == key) {
230 int drmSLLookupNeighbors(void *l, unsigned long key,
231 unsigned long *prev_key, void **prev_value,
232 unsigned long *next_key, void **next_value)
234 SkipListPtr list = (SkipListPtr)l;
235 SLEntryPtr update[SL_MAX_LEVEL + 1] = {0};
238 SLLocate(list, key, update);
240 *prev_key = *next_key = key;
241 *prev_value = *next_value = NULL;
244 *prev_key = update[0]->key;
245 *prev_value = update[0]->value;
247 if (update[0]->forward[0]) {
248 *next_key = update[0]->forward[0]->key;
249 *next_value = update[0]->forward[0]->value;
256 int drmSLNext(void *l, unsigned long *key, void **value)
258 SkipListPtr list = (SkipListPtr)l;
261 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
266 list->p0 = entry->forward[0];
268 *value = entry->value;
275 int drmSLFirst(void *l, unsigned long *key, void **value)
277 SkipListPtr list = (SkipListPtr)l;
279 if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
281 list->p0 = list->head->forward[0];
282 return drmSLNext(list, key, value);
285 /* Dump internal data structures for debugging. */
286 void drmSLDump(void *l)
288 SkipListPtr list = (SkipListPtr)l;
292 if (list->magic != SL_LIST_MAGIC) {
293 printf("Bad magic: 0x%08lx (expected 0x%08lx)\n",
294 list->magic, SL_LIST_MAGIC);
298 printf("Level = %d, count = %d\n", list->level, list->count);
299 for (entry = list->head; entry; entry = entry->forward[0]) {
300 if (entry->magic != SL_ENTRY_MAGIC) {
301 printf("Bad magic: 0x%08lx (expected 0x%08lx)\n",
302 list->magic, SL_ENTRY_MAGIC);
304 printf("\nEntry %p <0x%08lx, %p> has %2d levels\n",
305 entry, entry->key, entry->value, entry->levels);
306 for (i = 0; i < entry->levels; i++) {
307 if (entry->forward[i]) {
308 printf(" %2d: %p <0x%08lx, %p>\n",
311 entry->forward[i]->key,
312 entry->forward[i]->value);
314 printf(" %2d: %p\n", i, entry->forward[i]);