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/* glxhash.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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* 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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#include <X11/Xfuncproto.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 char *ps, rs[256]
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#define HASH_RANDOM_INIT(seed) ps = initstate(seed, rs, sizeof(rs))
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#define HASH_RANDOM random()
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#define HASH_RANDOM_DESTROY setstate(ps)
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#define HASH_RANDOM_DECL struct random_data rd; int32_t rv; char rs[256]
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#define HASH_RANDOM_INIT(seed) \
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(void) memset(&rd, 0, sizeof(rd)); \
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(void) initstate_r(seed, rs, sizeof(rs), &rd); \
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#define HASH_RANDOM ((void) random_r(&rd, &rv), rv)
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#define HASH_RANDOM_DESTROY
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typedef struct __glxHashBucket
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struct __glxHashBucket *next;
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} __glxHashBucket, *__glxHashBucketPtr;
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typedef struct __glxHashTable *__glxHashTablePtr;
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struct __glxHashTable
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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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__glxHashBucketPtr buckets[HASH_SIZE];
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__glxHashBucketPtr p1;
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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++)
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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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_X_HIDDEN __glxHashTable *
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__glxHashCreate(void)
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__glxHashTablePtr table;
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table = HASH_ALLOC(sizeof(*table));
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table->magic = HASH_MAGIC;
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for (i = 0; i < HASH_SIZE; i++)
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table->buckets[i] = NULL;
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__glxHashDestroy(__glxHashTable * t)
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__glxHashTablePtr table = (__glxHashTablePtr) t;
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__glxHashBucketPtr bucket;
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__glxHashBucketPtr next;
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if (table->magic != HASH_MAGIC)
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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 __glxHashBucketPtr
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HashFind(__glxHashTablePtr table, unsigned long key, unsigned long *h)
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unsigned long hash = HashHash(key);
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__glxHashBucketPtr prev = NULL;
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__glxHashBucketPtr 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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__glxHashLookup(__glxHashTable * t, unsigned long key, void **value)
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__glxHashTablePtr table = (__glxHashTablePtr) t;
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__glxHashBucketPtr bucket;
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if (!table || table->magic != HASH_MAGIC)
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return -1; /* Bad magic */
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bucket = HashFind(table, key, NULL);
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return 1; /* Not found */
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*value = bucket->value;
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return 0; /* Found */
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__glxHashInsert(__glxHashTable * t, unsigned long key, void *value)
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__glxHashTablePtr table = (__glxHashTablePtr) t;
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__glxHashBucketPtr bucket;
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if (table->magic != HASH_MAGIC)
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return -1; /* Bad magic */
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if (HashFind(table, key, &hash))
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return 1; /* Already in table */
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bucket = HASH_ALLOC(sizeof(*bucket));
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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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__glxHashDelete(__glxHashTable * t, unsigned long key)
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__glxHashTablePtr table = (__glxHashTablePtr) t;
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__glxHashBucketPtr bucket;
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if (table->magic != HASH_MAGIC)
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return -1; /* Bad magic */
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bucket = HashFind(table, key, &hash);
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return 1; /* Not found */
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table->buckets[hash] = bucket->next;
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__glxHashNext(__glxHashTable * t, unsigned long *key, void **value)
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__glxHashTablePtr table = (__glxHashTablePtr) t;
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while (table->p0 < HASH_SIZE) {
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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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table->p1 = table->buckets[table->p0];
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__glxHashFirst(__glxHashTable * t, unsigned long *key, void **value)
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__glxHashTablePtr table = (__glxHashTablePtr) t;
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if (table->magic != HASH_MAGIC)
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return -1; /* Bad magic */
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table->p1 = table->buckets[0];
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return __glxHashNext(table, key, value);
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#define DIST_LIMIT 10
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static int dist[DIST_LIMIT];
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for (i = 0; i < DIST_LIMIT; i++)
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count_entries(__glxHashBucketPtr bucket)
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for (; bucket; bucket = bucket->next)
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update_dist(int count)
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if (count >= DIST_LIMIT)
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++dist[DIST_LIMIT - 1];
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compute_dist(__glxHashTablePtr table)
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__glxHashBucketPtr bucket;
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printf("Hits = %ld, partials = %ld, misses = %ld\n",
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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)
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printf("%5d %10d\n", i, dist[i]);
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printf("other %10d\n", dist[i]);
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check_table(__glxHashTablePtr table, unsigned long key, unsigned long value)
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unsigned long retval = 0;
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int retcode = __glxHashLookup(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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__glxHashTablePtr table;
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printf("\n***** 256 consecutive integers ****\n");
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table = __glxHashCreate();
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for (i = 0; i < 256; i++)
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__glxHashInsert(table, i, i);
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for (i = 0; i < 256; i++)
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check_table(table, i, i);
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for (i = 256; i >= 0; i--)
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check_table(table, i, i);
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__glxHashDestroy(table);
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printf("\n***** 1024 consecutive integers ****\n");
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table = __glxHashCreate();
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for (i = 0; i < 1024; i++)
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__glxHashInsert(table, i, i);
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for (i = 0; i < 1024; i++)
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check_table(table, i, i);
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for (i = 1024; i >= 0; i--)
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check_table(table, i, i);
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__glxHashDestroy(table);
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printf("\n***** 1024 consecutive page addresses (4k pages) ****\n");
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table = __glxHashCreate();
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for (i = 0; i < 1024; i++)
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__glxHashInsert(table, i * 4096, i);
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for (i = 0; i < 1024; i++)
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check_table(table, i * 4096, i);
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for (i = 1024; i >= 0; i--)
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check_table(table, i * 4096, i);
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__glxHashDestroy(table);
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printf("\n***** 1024 random integers ****\n");
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table = __glxHashCreate();
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for (i = 0; i < 1024; i++)
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__glxHashInsert(table, random(), i);
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for (i = 0; i < 1024; i++)
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check_table(table, random(), i);
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for (i = 0; i < 1024; i++)
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check_table(table, random(), i);
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__glxHashDestroy(table);
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printf("\n***** 5000 random integers ****\n");
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table = __glxHashCreate();
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for (i = 0; i < 5000; i++)
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__glxHashInsert(table, random(), i);
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for (i = 0; i < 5000; i++)
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check_table(table, random(), i);
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for (i = 0; i < 5000; i++)
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check_table(table, random(), i);
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__glxHashDestroy(table);