/* glxhash.c -- Small hash table support for integer -> integer mapping * Taken from libdrm. * * 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 "glxhash.h" #include <X11/Xfuncproto.h> #define HASH_MAIN 0 #include <stdio.h> #include <stdlib.h> #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! */ #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 typedef struct __glxHashBucket { unsigned long key; void *value; struct __glxHashBucket *next; } __glxHashBucket, *__glxHashBucketPtr; typedef struct __glxHashTable *__glxHashTablePtr; struct __glxHashTable { unsigned long magic; unsigned long hits; /* At top of linked list */ unsigned long partials; /* Not at top of linked list */ unsigned long misses; /* Not in table */ __glxHashBucketPtr buckets[HASH_SIZE]; int p0; __glxHashBucketPtr p1; }; 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; } _X_HIDDEN __glxHashTable *__glxHashCreate(void) { __glxHashTablePtr table; int i; table = HASH_ALLOC(sizeof(*table)); if (!table) return NULL; table->magic = HASH_MAGIC; table->hits = 0; table->partials = 0; table->misses = 0; for (i = 0; i < HASH_SIZE; i++) table->buckets[i] = NULL; return table; } _X_HIDDEN int __glxHashDestroy(__glxHashTable *t) { __glxHashTablePtr table = (__glxHashTablePtr)t; __glxHashBucketPtr bucket; __glxHashBucketPtr 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 __glxHashBucketPtr HashFind(__glxHashTablePtr table, unsigned long key, unsigned long *h) { unsigned long hash = HashHash(key); __glxHashBucketPtr prev = NULL; __glxHashBucketPtr 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; } _X_HIDDEN int __glxHashLookup(__glxHashTable *t, unsigned long key, void **value) { __glxHashTablePtr table = (__glxHashTablePtr)t; __glxHashBucketPtr 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 */ } _X_HIDDEN int __glxHashInsert(__glxHashTable *t, unsigned long key, void *value) { __glxHashTablePtr table = (__glxHashTablePtr)t; __glxHashBucketPtr 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 */ } _X_HIDDEN int __glxHashDelete(__glxHashTable *t, unsigned long key) { __glxHashTablePtr table = (__glxHashTablePtr)t; unsigned long hash; __glxHashBucketPtr 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; } _X_HIDDEN int __glxHashNext(__glxHashTable *t, unsigned long *key, void **value) { __glxHashTablePtr table = (__glxHashTablePtr)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; } _X_HIDDEN int __glxHashFirst(__glxHashTable *t, unsigned long *key, void **value) { __glxHashTablePtr table = (__glxHashTablePtr)t; if (table->magic != HASH_MAGIC) return -1; /* Bad magic */ table->p0 = 0; table->p1 = table->buckets[0]; return __glxHashNext(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(__glxHashBucketPtr 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(__glxHashTablePtr table) { int i; __glxHashBucketPtr bucket; printf("Hits = %ld, partials = %ld, misses = %ld\n", 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(__glxHashTablePtr table, unsigned long key, unsigned long value) { unsigned long retval = 0; int retcode = __glxHashLookup(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) { __glxHashTablePtr table; int i; printf("\n***** 256 consecutive integers ****\n"); table = __glxHashCreate(); for (i = 0; i < 256; i++) __glxHashInsert(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); __glxHashDestroy(table); printf("\n***** 1024 consecutive integers ****\n"); table = __glxHashCreate(); for (i = 0; i < 1024; i++) __glxHashInsert(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); __glxHashDestroy(table); printf("\n***** 1024 consecutive page addresses (4k pages) ****\n"); table = __glxHashCreate(); for (i = 0; i < 1024; i++) __glxHashInsert(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); __glxHashDestroy(table); printf("\n***** 1024 random integers ****\n"); table = __glxHashCreate(); srandom(0xbeefbeef); for (i = 0; i < 1024; i++) __glxHashInsert(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); __glxHashDestroy(table); printf("\n***** 5000 random integers ****\n"); table = __glxHashCreate(); srandom(0xbeefbeef); for (i = 0; i < 5000; i++) __glxHashInsert(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); __glxHashDestroy(table); return 0; } #endif