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hashtable.c
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hashtable.c
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/***************************************************************************
*cr
*cr (C) Copyright 1995-2019 The Board of Trustees of the
*cr University of Illinois
*cr All Rights Reserved
*cr
***************************************************************************/
/***************************************************************************
* RCS INFORMATION:
*
* $RCSfile: hash.c,v $
* $Author: johns $ $Locker: $ $State: Exp $
* $Revision: 1.17 $ $Date: 2019/01/17 21:21:03 $
*
***************************************************************************
* DESCRIPTION:
* A simple hash table implementation for strings, contributed by John Stone,
* derived from his ray tracer code.
***************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "hashtable.h"
#define HASH_LIMIT 0.5
typedef struct hash_node_t {
int data; /* data in hash node */
const char * key; /* key for hash lookup */
struct hash_node_t *next; /* next node in hash chain */
} hash_node_t;
/*
* hash() - Hash function returns a hash number for a given key.
*
* tptr: Pointer to a hash table
* key: The key to create a hash number for
*/
static int hash(const hash_t *tptr, const char *key) {
int i=0;
int hashvalue;
while (*key != '\0')
i=(i<<3)+(*key++ - '0');
hashvalue = (((i*1103515249)>>tptr->downshift) & tptr->mask);
if (hashvalue < 0) {
hashvalue = 0;
}
return hashvalue;
}
/*
* hash_init() - Initialize a new hash table.
*
* tptr: Pointer to the hash table to initialize
* buckets: The number of initial buckets to create
*/
VMDEXTERNSTATIC void hash_init(hash_t *tptr, int buckets) {
/* make sure we allocate something */
if (buckets==0)
buckets=16;
/* initialize the table */
tptr->entries=0;
tptr->size=2;
tptr->mask=1;
tptr->downshift=29;
/* ensure buckets is a power of 2 */
while (tptr->size<buckets) {
tptr->size<<=1;
tptr->mask=(tptr->mask<<1)+1;
tptr->downshift--;
} /* while */
/* allocate memory for table */
tptr->bucket=(hash_node_t **) calloc(tptr->size, sizeof(hash_node_t *));
return;
}
/*
* rebuild_table() - Create new hash table when old one fills up.
*
* tptr: Pointer to a hash table
*/
static void rebuild_table(hash_t *tptr) {
hash_node_t **old_bucket, *old_hash, *tmp;
int old_size, h, i;
old_bucket=tptr->bucket;
old_size=tptr->size;
/* create a new table and rehash old buckets */
hash_init(tptr, old_size<<1);
for (i=0; i<old_size; i++) {
old_hash=old_bucket[i];
while(old_hash) {
tmp=old_hash;
old_hash=old_hash->next;
h=hash(tptr, tmp->key);
tmp->next=tptr->bucket[h];
tptr->bucket[h]=tmp;
tptr->entries++;
} /* while */
} /* for */
/* free memory used by old table */
free(old_bucket);
return;
}
/*
* hash_lookup() - Lookup an entry in the hash table and return a pointer to
* it or HASH_FAIL if it wasn't found.
*
* tptr: Pointer to the hash table
* key: The key to lookup
*/
VMDEXTERNSTATIC int hash_lookup(const hash_t *tptr, const char *key) {
int h;
hash_node_t *node;
/* find the entry in the hash table */
h=hash(tptr, key);
for (node=tptr->bucket[h]; node!=NULL; node=node->next) {
if (!strcmp(node->key, key))
break;
}
/* return the entry if it exists, or HASH_FAIL */
return(node ? node->data : HASH_FAIL);
}
/*
* hash_insert() - Insert an entry into the hash table. If the entry already
* exists return a pointer to it, otherwise return HASH_FAIL.
*
* tptr: A pointer to the hash table
* key: The key to insert into the hash table
* data: A pointer to the data to insert into the hash table
*/
VMDEXTERNSTATIC int hash_insert(hash_t *tptr, const char *key, int data) {
int tmp;
hash_node_t *node;
int h;
/* check to see if the entry exists */
if ((tmp=hash_lookup(tptr, key)) != HASH_FAIL)
return(tmp);
/* expand the table if needed */
while (tptr->entries>=HASH_LIMIT*tptr->size)
rebuild_table(tptr);
/* insert the new entry */
h=hash(tptr, key);
node=(struct hash_node_t *) malloc(sizeof(hash_node_t));
node->data=data;
node->key=key;
node->next=tptr->bucket[h];
tptr->bucket[h]=node;
tptr->entries++;
return HASH_FAIL;
}
/*
* hash_delete() - Remove an entry from a hash table and return a pointer
* to its data or HASH_FAIL if it wasn't found.
*
* tptr: A pointer to the hash table
* key: The key to remove from the hash table
*/
VMDEXTERNSTATIC int hash_delete(hash_t *tptr, const char *key) {
hash_node_t *node, *last;
int data;
int h;
/* find the node to remove */
h=hash(tptr, key);
for (node=tptr->bucket[h]; node; node=node->next) {
if (!strcmp(node->key, key))
break;
}
/* Didn't find anything, return HASH_FAIL */
if (node==NULL)
return HASH_FAIL;
/* if node is at head of bucket, we have it easy */
if (node==tptr->bucket[h])
tptr->bucket[h]=node->next;
else {
/* find the node before the node we want to remove */
for (last=tptr->bucket[h]; last && last->next; last=last->next) {
if (last->next==node)
break;
}
last->next=node->next;
}
/* free memory and return the data */
data=node->data;
free(node);
return(data);
}
/*
* inthash_entries() - return the number of hash table entries.
*
*/
VMDEXTERNSTATIC int hash_entries(hash_t *tptr) {
return tptr->entries;
}
/*
* hash_destroy() - Delete the entire table, and all remaining entries.
*
*/
VMDEXTERNSTATIC void hash_destroy(hash_t *tptr) {
hash_node_t *node, *last;
int i;
for (i=0; i<tptr->size; i++) {
node = tptr->bucket[i];
while (node != NULL) {
last = node;
node = node->next;
free(last);
}
}
/* free the entire array of buckets */
if (tptr->bucket != NULL) {
free(tptr->bucket);
memset(tptr, 0, sizeof(hash_t));
}
}
/*
* alos() - Find the average length of search.
*
* tptr: Pointer to a hash table
*/
static float alos(hash_t *tptr) {
int i,j;
float alos=0;
hash_node_t *node;
for (i=0; i<tptr->size; i++) {
for (node=tptr->bucket[i], j=0; node!=NULL; node=node->next, j++);
if (j)
alos+=((j*(j+1))>>1);
} /* for */
return(tptr->entries ? alos/tptr->entries : 0);
}
/*
* hash_stats() - Return a string with stats about a hash table.
*
* tptr: A pointer to the hash table
*/
VMDEXTERNSTATIC char * hash_stats(hash_t *tptr) {
static char buf[1024];
sprintf(buf, "%u slots, %u entries, and %1.2f ALOS",
(int)tptr->size, (int)tptr->entries, alos(tptr));
return(buf);
}