/* 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 "libdrm_macros.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;

}

drm_public 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;

}

drm_public 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];

}

drm_public 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 */

}

drm_public 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;

}

drm_public 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;

}

drm_public 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;

}

drm_public 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;

}

drm_public 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. */

drm_public 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]);

	    }

	}

    }

}