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/* xf86drmHash.c -- Small hash table support for integer -> integer mapping
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* Created: Sun Apr 18 09:35:45 1999 by faith@precisioninsight.com
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* Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
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* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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* Authors: Rickard E. (Rik) Faith <faith@valinux.com>
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* $XFree86: xc/programs/Xserver/hw/xfree86/os-support/linux/drm/xf86drmHash.c,v 1.4 2001/03/21 18:08:54 dawes Exp $
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* This file contains a straightforward implementation of a fixed-sized
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* hash table using self-organizing linked lists [Knuth73, pp. 398-399] for
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* collision resolution. There are two potentially interesting things
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* about this implementation:
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* 1) The table is power-of-two sized. Prime sized tables are more
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* traditional, but do not have a significant advantage over power-of-two
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* sized table, especially when double hashing is not used for collision
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* 2) The hash computation uses a table of random integers [Hanson97,
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* With a table size of 512, the current implementation is sufficient for a
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* few hundred keys. Since this is well above the expected size of the
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* tables for which this implementation was designed, the implementation of
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* dynamic hash tables was postponed until the need arises. A common (and
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* naive) approach to dynamic hash table implementation simply creates a
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* new hash table when necessary, rehashes all the data into the new table,
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* and destroys the old table. The approach in [Larson88] is superior in
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* two ways: 1) only a portion of the table is expanded when needed,
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* distributing the expansion cost over several insertions, and 2) portions
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* of the table can be locked, enabling a scalable thread-safe
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* [Hanson97] David R. Hanson. C Interfaces and Implementations:
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* Techniques for Creating Reusable Software. Reading, Massachusetts:
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* Addison-Wesley, 1997.
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* [Knuth73] Donald E. Knuth. The Art of Computer Programming. Volume 3:
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* Sorting and Searching. Reading, Massachusetts: Addison-Wesley, 1973.
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* [Larson88] Per-Ake Larson. "Dynamic Hash Tables". CACM 31(4), April
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#ifdef HAVE_XORG_CONFIG_H
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#include <xorg-config.h>
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# include "xf86_ansic.h"
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#define HASH_MAGIC 0xdeadbeef
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#define HASH_SIZE 512 /* Good for about 100 entries */
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/* If you change this value, you probably
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have to change the HashHash hashing
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#define HASH_ALLOC malloc
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#define HASH_FREE free
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#define HASH_RANDOM_DECL
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#define HASH_RANDOM_INIT(seed) srandom(seed)
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#define HASH_RANDOM random()
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#define HASH_ALLOC drmMalloc
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#define HASH_FREE drmFree
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#define HASH_RANDOM_DECL void *state
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#define HASH_RANDOM_INIT(seed) state = drmRandomCreate(seed)
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#define HASH_RANDOM drmRandom(state)
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typedef struct HashBucket {
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struct HashBucket *next;
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} HashBucket, *HashBucketPtr;
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typedef struct HashTable {
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unsigned long entries;
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unsigned long hits; /* At top of linked list */
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unsigned long partials; /* Not at top of linked list */
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unsigned long misses; /* Not in table */
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HashBucketPtr buckets[HASH_SIZE];
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} HashTable, *HashTablePtr;
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extern void *N(HashCreate)(void);
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extern int N(HashDestroy)(void *t);
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extern int N(HashLookup)(void *t, unsigned long key, unsigned long *value);
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extern int N(HashInsert)(void *t, unsigned long key, unsigned long value);
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extern int N(HashDelete)(void *t, unsigned long key);
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static unsigned long HashHash(unsigned long key)
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unsigned long hash = 0;
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unsigned long tmp = key;
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static unsigned long scatter[256];
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HASH_RANDOM_INIT(37);
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for (i = 0; i < 256; i++) scatter[i] = HASH_RANDOM;
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hash = (hash << 1) + scatter[tmp & 0xff];
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printf( "Hash(%d) = %d\n", key, hash);
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void *N(HashCreate)(void)
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table = HASH_ALLOC(sizeof(*table));
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if (!table) return NULL;
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table->magic = HASH_MAGIC;
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for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = NULL;
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int N(HashDestroy)(void *t)
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HashTablePtr table = (HashTablePtr)t;
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HashBucketPtr bucket;
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if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
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for (i = 0; i < HASH_SIZE; i++) {
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for (bucket = table->buckets[i]; bucket;) {
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/* Find the bucket and organize the list so that this bucket is at the
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static HashBucketPtr HashFind(HashTablePtr table,
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unsigned long key, unsigned long *h)
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unsigned long hash = HashHash(key);
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HashBucketPtr prev = NULL;
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HashBucketPtr bucket;
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for (bucket = table->buckets[hash]; bucket; bucket = bucket->next) {
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if (bucket->key == key) {
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prev->next = bucket->next;
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bucket->next = table->buckets[hash];
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table->buckets[hash] = bucket;
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int N(HashLookup)(void *t, unsigned long key, void **value)
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HashTablePtr table = (HashTablePtr)t;
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HashBucketPtr bucket;
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if (!table || table->magic != HASH_MAGIC) return -1; /* Bad magic */
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bucket = HashFind(table, key, NULL);
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if (!bucket) return 1; /* Not found */
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*value = bucket->value;
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return 0; /* Found */
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int N(HashInsert)(void *t, unsigned long key, void *value)
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HashTablePtr table = (HashTablePtr)t;
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HashBucketPtr bucket;
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if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
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if (HashFind(table, key, &hash)) return 1; /* Already in table */
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bucket = HASH_ALLOC(sizeof(*bucket));
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if (!bucket) return -1; /* Error */
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bucket->value = value;
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bucket->next = table->buckets[hash];
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table->buckets[hash] = bucket;
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printf("Inserted %d at %d/%p\n", key, hash, bucket);
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return 0; /* Added to table */
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int N(HashDelete)(void *t, unsigned long key)
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HashTablePtr table = (HashTablePtr)t;
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HashBucketPtr bucket;
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if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
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bucket = HashFind(table, key, &hash);
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if (!bucket) return 1; /* Not found */
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table->buckets[hash] = bucket->next;
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int N(HashNext)(void *t, unsigned long *key, void **value)
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HashTablePtr table = (HashTablePtr)t;
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for (; table->p0 < HASH_SIZE;
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++table->p0, table->p1 = table->buckets[table->p0]) {
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*key = table->p1->key;
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*value = table->p1->value;
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table->p1 = table->p1->next;
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int N(HashFirst)(void *t, unsigned long *key, void **value)
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HashTablePtr table = (HashTablePtr)t;
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if (table->magic != HASH_MAGIC) return -1; /* Bad magic */
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table->p1 = table->buckets[0];
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return N(HashNext)(table, key, value);
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#define DIST_LIMIT 10
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static int dist[DIST_LIMIT];
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static void clear_dist(void) {
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for (i = 0; i < DIST_LIMIT; i++) dist[i] = 0;
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static int count_entries(HashBucketPtr bucket)
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for (; bucket; bucket = bucket->next) ++count;
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static void update_dist(int count)
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if (count >= DIST_LIMIT) ++dist[DIST_LIMIT-1];
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static void compute_dist(HashTablePtr table)
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HashBucketPtr bucket;
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printf("Entries = %ld, hits = %ld, partials = %ld, misses = %ld\n",
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table->entries, table->hits, table->partials, table->misses);
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for (i = 0; i < HASH_SIZE; i++) {
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bucket = table->buckets[i];
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update_dist(count_entries(bucket));
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for (i = 0; i < DIST_LIMIT; i++) {
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if (i != DIST_LIMIT-1) printf("%5d %10d\n", i, dist[i]);
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else printf("other %10d\n", dist[i]);
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static void check_table(HashTablePtr table,
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unsigned long key, unsigned long value)
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unsigned long retval = 0;
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int retcode = N(HashLookup)(table, key, &retval);
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printf("Bad magic = 0x%08lx:"
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" key = %lu, expected = %lu, returned = %lu\n",
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table->magic, key, value, retval);
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printf("Not found: key = %lu, expected = %lu returned = %lu\n",
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printf("Bad value: key = %lu, expected = %lu, returned = %lu\n",
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printf("Bad retcode = %d: key = %lu, expected = %lu, returned = %lu\n",
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retcode, key, value, retval);
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printf("\n***** 256 consecutive integers ****\n");
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table = N(HashCreate)();
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for (i = 0; i < 256; i++) N(HashInsert)(table, i, i);
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for (i = 0; i < 256; i++) check_table(table, i, i);
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for (i = 256; i >= 0; i--) check_table(table, i, i);
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N(HashDestroy)(table);
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printf("\n***** 1024 consecutive integers ****\n");
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table = N(HashCreate)();
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for (i = 0; i < 1024; i++) N(HashInsert)(table, i, i);
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for (i = 0; i < 1024; i++) check_table(table, i, i);
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for (i = 1024; i >= 0; i--) check_table(table, i, i);
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N(HashDestroy)(table);
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printf("\n***** 1024 consecutive page addresses (4k pages) ****\n");
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table = N(HashCreate)();
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for (i = 0; i < 1024; i++) N(HashInsert)(table, i*4096, i);
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for (i = 0; i < 1024; i++) check_table(table, i*4096, i);
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for (i = 1024; i >= 0; i--) check_table(table, i*4096, i);
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N(HashDestroy)(table);
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printf("\n***** 1024 random integers ****\n");
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table = N(HashCreate)();
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for (i = 0; i < 1024; i++) N(HashInsert)(table, random(), i);
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for (i = 0; i < 1024; i++) check_table(table, random(), i);
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for (i = 0; i < 1024; i++) check_table(table, random(), i);
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N(HashDestroy)(table);
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printf("\n***** 5000 random integers ****\n");
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table = N(HashCreate)();
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for (i = 0; i < 5000; i++) N(HashInsert)(table, random(), i);
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for (i = 0; i < 5000; i++) check_table(table, random(), i);
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for (i = 0; i < 5000; i++) check_table(table, random(), i);
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N(HashDestroy)(table);