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+/* 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>
+
+#define HASH_MAIN 0
+
+#if !HASH_MAIN
+# include "xf86drm.h"
+#endif
+
+#define HASH_MAGIC 0xdeadbeef
+#define HASH_DEBUG 0
+#define HASH_SIZE 512 /* Good for about 100 entries */
+ /* If you change this value, you probably
+ have to change the HashHash hashing
+ function! */
+
+#if HASH_MAIN
+#define HASH_ALLOC malloc
+#define HASH_FREE free
+#define HASH_RANDOM_DECL
+#define HASH_RANDOM_INIT(seed) srandom(seed)
+#define HASH_RANDOM random()
+#define HASH_RANDOM_DESTROY
+#else
+#define HASH_ALLOC drmMalloc
+#define HASH_FREE drmFree
+#define HASH_RANDOM_DECL void *state
+#define HASH_RANDOM_INIT(seed) state = drmRandomCreate(seed)
+#define HASH_RANDOM drmRandom(state)
+#define HASH_RANDOM_DESTROY drmRandomDestroy(state)
+
+#endif
+
+typedef struct HashBucket {
+ unsigned long key;
+ void *value;
+ struct HashBucket *next;
+} HashBucket, *HashBucketPtr;
+
+typedef struct HashTable {
+ unsigned long magic;
+ unsigned long entries;
+ unsigned long hits; /* At top of linked list */
+ unsigned long partials; /* Not at top of linked list */
+ unsigned long misses; /* Not in table */
+ HashBucketPtr buckets[HASH_SIZE];
+ int p0;
+ HashBucketPtr p1;
+} HashTable, *HashTablePtr;
+
+#if HASH_MAIN
+extern void *drmHashCreate(void);
+extern int drmHashDestroy(void *t);
+extern int drmHashLookup(void *t, unsigned long key, unsigned long *value);
+extern int drmHashInsert(void *t, unsigned long key, unsigned long value);
+extern int drmHashDelete(void *t, unsigned long key);
+#endif
+
+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) {
+ HASH_RANDOM_DECL;
+ HASH_RANDOM_INIT(37);
+ for (i = 0; i < 256; i++) scatter[i] = HASH_RANDOM;
+ HASH_RANDOM_DESTROY;
+ ++init;
+ }
+
+ while (tmp) {
+ hash = (hash << 1) + scatter[tmp & 0xff];
+ tmp >>= 8;
+ }
+
+ hash %= HASH_SIZE;
+#if HASH_DEBUG
+ printf( "Hash(%d) = %d\n", key, hash);
+#endif
+ return hash;
+}
+
+void *drmHashCreate(void)
+{
+ HashTablePtr table;
+ int i;
+
+ table = HASH_ALLOC(sizeof(*table));
+ if (!table) return NULL;
+ table->magic = HASH_MAGIC;
+ table->entries = 0;
+ table->hits = 0;
+ table->partials = 0;
+ table->misses = 0;
+
+ for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = NULL;
+ return table;
+}
+
+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;
+ HASH_FREE(bucket);
+ bucket = next;
+ }
+ }
+ HASH_FREE(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;
+}
+
+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 */
+}
+
+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 = HASH_ALLOC(sizeof(*bucket));
+ if (!bucket) return -1; /* Error */
+ bucket->key = key;
+ bucket->value = value;
+ bucket->next = table->buckets[hash];
+ table->buckets[hash] = bucket;
+#if HASH_DEBUG
+ printf("Inserted %d at %d/%p\n", key, hash, bucket);
+#endif
+ return 0; /* Added to table */
+}
+
+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;
+ HASH_FREE(bucket);
+ return 0;
+}
+
+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;
+}
+
+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);
+}
+
+#if HASH_MAIN
+#define DIST_LIMIT 10
+static int dist[DIST_LIMIT];
+
+static void clear_dist(void) {
+ int i;
+
+ for (i = 0; i < DIST_LIMIT; i++) dist[i] = 0;
+}
+
+static int count_entries(HashBucketPtr bucket)
+{
+ int count = 0;
+
+ for (; bucket; bucket = bucket->next) ++count;
+ return count;
+}
+
+static void update_dist(int count)
+{
+ if (count >= DIST_LIMIT) ++dist[DIST_LIMIT-1];
+ else ++dist[count];
+}
+
+static void compute_dist(HashTablePtr table)
+{
+ int i;
+ HashBucketPtr bucket;
+
+ printf("Entries = %ld, hits = %ld, partials = %ld, misses = %ld\n",
+ table->entries, table->hits, table->partials, table->misses);
+ clear_dist();
+ for (i = 0; i < HASH_SIZE; i++) {
+ bucket = table->buckets[i];
+ update_dist(count_entries(bucket));
+ }
+ for (i = 0; i < DIST_LIMIT; i++) {
+ if (i != DIST_LIMIT-1) printf("%5d %10d\n", i, dist[i]);
+ else printf("other %10d\n", dist[i]);
+ }
+}
+
+static void check_table(HashTablePtr table,
+ unsigned long key, unsigned long value)
+{
+ unsigned long retval = 0;
+ int retcode = drmHashLookup(table, key, &retval);
+
+ switch (retcode) {
+ case -1:
+ printf("Bad magic = 0x%08lx:"
+ " key = %lu, expected = %lu, returned = %lu\n",
+ table->magic, key, value, retval);
+ break;
+ case 1:
+ printf("Not found: key = %lu, expected = %lu returned = %lu\n",
+ key, value, retval);
+ break;
+ case 0:
+ if (value != retval)
+ printf("Bad value: key = %lu, expected = %lu, returned = %lu\n",
+ key, value, retval);
+ break;
+ default:
+ printf("Bad retcode = %d: key = %lu, expected = %lu, returned = %lu\n",
+ retcode, key, value, retval);
+ break;
+ }
+}
+
+int main(void)
+{
+ HashTablePtr table;
+ int i;
+
+ printf("\n***** 256 consecutive integers ****\n");
+ table = drmHashCreate();
+ for (i = 0; i < 256; i++) drmHashInsert(table, i, i);
+ for (i = 0; i < 256; i++) check_table(table, i, i);
+ for (i = 256; i >= 0; i--) check_table(table, i, i);
+ compute_dist(table);
+ drmHashDestroy(table);
+
+ printf("\n***** 1024 consecutive integers ****\n");
+ table = drmHashCreate();
+ for (i = 0; i < 1024; i++) drmHashInsert(table, i, i);
+ for (i = 0; i < 1024; i++) check_table(table, i, i);
+ for (i = 1024; i >= 0; i--) check_table(table, i, i);
+ compute_dist(table);
+ drmHashDestroy(table);
+
+ printf("\n***** 1024 consecutive page addresses (4k pages) ****\n");
+ table = drmHashCreate();
+ for (i = 0; i < 1024; i++) drmHashInsert(table, i*4096, i);
+ for (i = 0; i < 1024; i++) check_table(table, i*4096, i);
+ for (i = 1024; i >= 0; i--) check_table(table, i*4096, i);
+ compute_dist(table);
+ drmHashDestroy(table);
+
+ printf("\n***** 1024 random integers ****\n");
+ table = drmHashCreate();
+ srandom(0xbeefbeef);
+ for (i = 0; i < 1024; i++) drmHashInsert(table, random(), i);
+ srandom(0xbeefbeef);
+ for (i = 0; i < 1024; i++) check_table(table, random(), i);
+ srandom(0xbeefbeef);
+ for (i = 0; i < 1024; i++) check_table(table, random(), i);
+ compute_dist(table);
+ drmHashDestroy(table);
+
+ printf("\n***** 5000 random integers ****\n");
+ table = drmHashCreate();
+ srandom(0xbeefbeef);
+ for (i = 0; i < 5000; i++) drmHashInsert(table, random(), i);
+ srandom(0xbeefbeef);
+ for (i = 0; i < 5000; i++) check_table(table, random(), i);
+ srandom(0xbeefbeef);
+ for (i = 0; i < 5000; i++) check_table(table, random(), i);
+ compute_dist(table);
+ drmHashDestroy(table);
+
+ return 0;
+}
+#endif
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