/* xf86drmHash.c -- Small hash table support for integer -> integer mapping

 * Created: Sun Apr 18 09:35:45 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 implementation of a fixed-sized

 * hash table using self-organizing linked lists [Knuth73, pp. 398-399] for

 * collision resolution.  There are two potentially interesting things

 * about this implementation:

 *

 * 1) The table is power-of-two sized.  Prime sized tables are more

 * traditional, but do not have a significant advantage over power-of-two

 * sized table, especially when double hashing is not used for collision

 * resolution.

 *

 * 2) The hash computation uses a table of random integers [Hanson97,

 * pp. 39-41].

 *

 * FUTURE ENHANCEMENTS

 *

 * With a table size of 512, the current implementation is sufficient for a

 * few hundred keys.  Since this is well above the expected size of the

 * tables for which this implementation was designed, the implementation of

 * dynamic hash tables was postponed until the need arises.  A common (and

 * naive) approach to dynamic hash table implementation simply creates a

 * new hash table when necessary, rehashes all the data into the new table,

 * and destroys the old table.  The approach in [Larson88] is superior in

 * two ways: 1) only a portion of the table is expanded when needed,

 * distributing the expansion cost over several insertions, and 2) portions

 * of the table can be locked, enabling a scalable thread-safe

 * implementation.

 *

 * REFERENCES

 *

 * [Hanson97] David R. Hanson.  C Interfaces and Implementations:

 * Techniques for Creating Reusable Software.  Reading, Massachusetts:

 * Addison-Wesley, 1997.

 *

 * [Knuth73] Donald E. Knuth. The Art of Computer Programming.  Volume 3:

 * Sorting and Searching.  Reading, Massachusetts: Addison-Wesley, 1973.

 *

 * [Larson88] Per-Ake Larson. "Dynamic Hash Tables".  CACM 31(4), April

 * 1988, pp. 446-457.

 *

 */

#include <stdio.h>

#include <stdlib.h>

#include "libdrm_macros.h"

#include "xf86drm.h"

#include "xf86drmHash.h"

#define HASH_MAGIC 0xdeadbeef

static unsigned long HashHash(unsigned long key)

{

    unsigned long        hash = 0;

    unsigned long        tmp  = key;

    static int           init = 0;

    static unsigned long scatter[256];

    int                  i;

    if (!init) {

	void *state;

	state = drmRandomCreate(37);

	for (i = 0; i < 256; i++) scatter[i] = drmRandom(state);

	drmRandomDestroy(state);

	++init;

    }

    while (tmp) {

	hash = (hash << 1) + scatter[tmp & 0xff];

	tmp >>= 8;

    }

    hash %= HASH_SIZE;

    return hash;

}

drm_public void *drmHashCreate(void)

{

    HashTablePtr table;

    table           = drmMalloc(sizeof(*table));

    if (!table) return NULL;

    table->magic    = HASH_MAGIC;

    return table;

}

drm_public int drmHashDestroy(void *t)

{

    HashTablePtr  table = (HashTablePtr)t;

    HashBucketPtr bucket;

    HashBucketPtr next;

    int           i;

    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */

    for (i = 0; i < HASH_SIZE; i++) {

	for (bucket = table->buckets[i]; bucket;) {

	    next = bucket->next;

	    drmFree(bucket);

	    bucket = next;

	}

    }

    drmFree(table);

    return 0;

}

/* Find the bucket and organize the list so that this bucket is at the

   top. */

static HashBucketPtr HashFind(HashTablePtr table,

			      unsigned long key, unsigned long *h)

{

    unsigned long hash = HashHash(key);

    HashBucketPtr prev = NULL;

    HashBucketPtr bucket;

    if (h) *h = hash;

    for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) {

	if (bucket->key == key) {

	    if (prev) {

				/* Organize */

		prev->next           = bucket->next;

		bucket->next         = table->buckets[hash];

		table->buckets[hash] = bucket;

		++table->partials;

	    } else {

		++table->hits;

	    }

	    return bucket;

	}

	prev = bucket;

    }

    ++table->misses;

    return NULL;

}

drm_public int drmHashLookup(void *t, unsigned long key, void **value)

{

    HashTablePtr  table = (HashTablePtr)t;

    HashBucketPtr bucket;

    if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */

    bucket = HashFind(table, key, NULL);

    if (!bucket) return 1;	/* Not found */

    *value = bucket->value;

    return 0;			/* Found */

}

drm_public int drmHashInsert(void *t, unsigned long key, void *value)

{

    HashTablePtr  table = (HashTablePtr)t;

    HashBucketPtr bucket;

    unsigned long hash;

    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */

    if (HashFind(table, key, &hash)) return 1; /* Already in table */

    bucket               = drmMalloc(sizeof(*bucket));

    if (!bucket) return -1;	/* Error */

    bucket->key          = key;

    bucket->value        = value;

    bucket->next         = table->buckets[hash];

    table->buckets[hash] = bucket;

    return 0;			/* Added to table */

}

drm_public int drmHashDelete(void *t, unsigned long key)

{

    HashTablePtr  table = (HashTablePtr)t;

    unsigned long hash;

    HashBucketPtr bucket;

    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */

    bucket = HashFind(table, key, &hash);

    if (!bucket) return 1;	/* Not found */

    table->buckets[hash] = bucket->next;

    drmFree(bucket);

    return 0;

}

drm_public int drmHashNext(void *t, unsigned long *key, void **value)

{

    HashTablePtr  table = (HashTablePtr)t;

    while (table->p0 < HASH_SIZE) {

	if (table->p1) {

	    *key       = table->p1->key;

	    *value     = table->p1->value;

	    table->p1  = table->p1->next;

	    return 1;

	}

	table->p1 = table->buckets[table->p0];

	++table->p0;

    }

    return 0;

}

drm_public int drmHashFirst(void *t, unsigned long *key, void **value)

{

    HashTablePtr  table = (HashTablePtr)t;

    if (table->magic != HASH_MAGIC) return -1; /* Bad magic */

    table->p0 = 0;

    table->p1 = table->buckets[0];

    return drmHashNext(table, key, value);

}