/* xf86drmSL.c -- Skip list support
* Created: Mon May 10 09:28:13 1999 by faith@precisioninsight.com
*
* Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
* All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*
* Authors: Rickard E. (Rik) Faith <faith@valinux.com>
*
* DESCRIPTION
*
* This file contains a straightforward skip list implementation.n
*
* FUTURE ENHANCEMENTS
*
* REFERENCES
*
* [Pugh90] William Pugh. Skip Lists: A Probabilistic Alternative to
* Balanced Trees. CACM 33(6), June 1990, pp. 668-676.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include "xf86drm.h"
#define SL_LIST_MAGIC 0xfacade00LU
#define SL_ENTRY_MAGIC 0x00fab1edLU
#define SL_FREED_MAGIC 0xdecea5edLU
#define SL_MAX_LEVEL 16
#define SL_RANDOM_SEED 0xc01055a1LU
#define SL_RANDOM_DECL static void *state = NULL
#define SL_RANDOM_INIT(seed) if (!state) state = drmRandomCreate(seed)
#define SL_RANDOM drmRandom(state)
typedef struct SLEntry {
unsigned long magic; /* SL_ENTRY_MAGIC */
unsigned long key;
void *value;
int levels;
struct SLEntry *forward[1]; /* variable sized array */
} SLEntry, *SLEntryPtr;
typedef struct SkipList {
unsigned long magic; /* SL_LIST_MAGIC */
int level;
int count;
SLEntryPtr head;
SLEntryPtr p0; /* Position for iteration */
} SkipList, *SkipListPtr;
static SLEntryPtr SLCreateEntry(int max_level, unsigned long key, void *value)
{
SLEntryPtr entry;
if (max_level < 0 || max_level > SL_MAX_LEVEL) max_level = SL_MAX_LEVEL;
entry = drmMalloc(sizeof(*entry)
+ (max_level + 1) * sizeof(entry->forward[0]));
if (!entry) return NULL;
entry->magic = SL_ENTRY_MAGIC;
entry->key = key;
entry->value = value;
entry->levels = max_level + 1;
return entry;
}
static int SLRandomLevel(void)
{
int level = 1;
SL_RANDOM_DECL;
SL_RANDOM_INIT(SL_RANDOM_SEED);
while ((SL_RANDOM & 0x01) && level < SL_MAX_LEVEL) ++level;
return level;
}
void *drmSLCreate(void)
{
SkipListPtr list;
int i;
list = drmMalloc(sizeof(*list));
if (!list) return NULL;
list->magic = SL_LIST_MAGIC;
list->level = 0;
list->head = SLCreateEntry(SL_MAX_LEVEL, 0, NULL);
list->count = 0;
for (i = 0; i <= SL_MAX_LEVEL; i++) list->head->forward[i] = NULL;
return list;
}
int drmSLDestroy(void *l)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr entry;
SLEntryPtr next;
if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
for (entry = list->head; entry; entry = next) {
if (entry->magic != SL_ENTRY_MAGIC) return -1; /* Bad magic */
next = entry->forward[0];
entry->magic = SL_FREED_MAGIC;
drmFree(entry);
}
list->magic = SL_FREED_MAGIC;
drmFree(list);
return 0;
}
static SLEntryPtr SLLocate(void *l, unsigned long key, SLEntryPtr *update)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr entry;
int i;
if (list->magic != SL_LIST_MAGIC) return NULL;
for (i = list->level, entry = list->head; i >= 0; i--) {
while (entry->forward[i] && entry->forward[i]->key < key)
entry = entry->forward[i];
update[i] = entry;
}
return entry->forward[0];
}
int drmSLInsert(void *l, unsigned long key, void *value)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr entry;
SLEntryPtr update[SL_MAX_LEVEL + 1];
int level;
int i;
if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
entry = SLLocate(list, key, update);
if (entry && entry->key == key) return 1; /* Already in list */
level = SLRandomLevel();
if (level > list->level) {
level = ++list->level;
update[level] = list->head;
}
entry = SLCreateEntry(level, key, value);
/* Fix up forward pointers */
for (i = 0; i <= level; i++) {
entry->forward[i] = update[i]->forward[i];
update[i]->forward[i] = entry;
}
++list->count;
return 0; /* Added to table */
}
int drmSLDelete(void *l, unsigned long key)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr update[SL_MAX_LEVEL + 1];
SLEntryPtr entry;
int i;
if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
entry = SLLocate(list, key, update);
if (!entry || entry->key != key) return 1; /* Not found */
/* Fix up forward pointers */
for (i = 0; i <= list->level; i++) {
if (update[i]->forward[i] == entry)
update[i]->forward[i] = entry->forward[i];
}
entry->magic = SL_FREED_MAGIC;
drmFree(entry);
while (list->level && !list->head->forward[list->level]) --list->level;
--list->count;
return 0;
}
int drmSLLookup(void *l, unsigned long key, void **value)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr update[SL_MAX_LEVEL + 1];
SLEntryPtr entry;
entry = SLLocate(list, key, update);
if (entry && entry->key == key) {
*value = entry;
return 0;
}
*value = NULL;
return -1;
}
int drmSLLookupNeighbors(void *l, unsigned long key,
unsigned long *prev_key, void **prev_value,
unsigned long *next_key, void **next_value)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr update[SL_MAX_LEVEL + 1] = {0};
int retcode = 0;
SLLocate(list, key, update);
*prev_key = *next_key = key;
*prev_value = *next_value = NULL;
if (update[0]) {
*prev_key = update[0]->key;
*prev_value = update[0]->value;
++retcode;
if (update[0]->forward[0]) {
*next_key = update[0]->forward[0]->key;
*next_value = update[0]->forward[0]->value;
++retcode;
}
}
return retcode;
}
int drmSLNext(void *l, unsigned long *key, void **value)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr entry;
if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
entry = list->p0;
if (entry) {
list->p0 = entry->forward[0];
*key = entry->key;
*value = entry->value;
return 1;
}
list->p0 = NULL;
return 0;
}
int drmSLFirst(void *l, unsigned long *key, void **value)
{
SkipListPtr list = (SkipListPtr)l;
if (list->magic != SL_LIST_MAGIC) return -1; /* Bad magic */
list->p0 = list->head->forward[0];
return drmSLNext(list, key, value);
}
/* Dump internal data structures for debugging. */
void drmSLDump(void *l)
{
SkipListPtr list = (SkipListPtr)l;
SLEntryPtr entry;
int i;
if (list->magic != SL_LIST_MAGIC) {
printf("Bad magic: 0x%08lx (expected 0x%08lx)\n",
list->magic, SL_LIST_MAGIC);
return;
}
printf("Level = %d, count = %d\n", list->level, list->count);
for (entry = list->head; entry; entry = entry->forward[0]) {
if (entry->magic != SL_ENTRY_MAGIC) {
printf("Bad magic: 0x%08lx (expected 0x%08lx)\n",
list->magic, SL_ENTRY_MAGIC);
}
printf("\nEntry %p <0x%08lx, %p> has %2d levels\n",
entry, entry->key, entry->value, entry->levels);
for (i = 0; i < entry->levels; i++) {
if (entry->forward[i]) {
printf(" %2d: %p <0x%08lx, %p>\n",
i,
entry->forward[i],
entry->forward[i]->key,
entry->forward[i]->value);
} else {
printf(" %2d: %p\n", i, entry->forward[i]);
}
}
}
}