1 /************************************************************************
2 Copyright 1988, 1991 by Carnegie Mellon University
6 Permission to use, copy, modify, and distribute this software and its
7 documentation for any purpose and without fee is hereby granted, provided
8 that the above copyright notice appear in all copies and that both that
9 copyright notice and this permission notice appear in supporting
10 documentation, and that the name of Carnegie Mellon University not be used
11 in advertising or publicity pertaining to distribution of the software
12 without specific, written prior permission.
14 CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
15 SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.
16 IN NO EVENT SHALL CMU BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
17 DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
18 PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
19 ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
24 ************************************************************************/
27 * Generalized hash table ADT
29 * Provides multiple, dynamically-allocated, variable-sized hash tables on
30 * various data and keys.
32 * This package attempts to follow some of the coding conventions suggested
33 * by Bob Sidebotham and the AFS Clean Code Committee of the
34 * Information Technology Center at Carnegie Mellon.
38 #include <sys/types.h>
51 * This can be changed to make internal routines visible to debuggers, etc.
54 #define PRIVATE static
57 PRIVATE void hashi_FreeMembers(hash_member *, hash_freefp);
63 * Hash table initialization routine.
65 * This routine creates and intializes a hash table of size "tablesize"
66 * entries. Successful calls return a pointer to the hash table (which must
67 * be passed to other hash routines to identify the hash table). Failed
79 totalsize = sizeof(hash_tbl)
80 + sizeof(hash_member *) * (tablesize - 1);
81 hashtblptr = (hash_tbl *) malloc(totalsize);
83 bzero((char *) hashtblptr, totalsize);
84 hashtblptr->size = tablesize; /* Success! */
85 hashtblptr->bucketnum = 0;
86 hashtblptr->member = (hashtblptr->table)[0];
89 hashtblptr = NULL; /* Disallow zero-length tables */
91 return hashtblptr; /* NULL if failure */
97 * Frees an entire linked list of bucket members (used in the open
98 * hashing scheme). Does nothing if the passed pointer is NULL.
102 hashi_FreeMembers(bucketptr, free_data)
103 hash_member *bucketptr;
104 hash_freefp free_data;
106 hash_member *nextbucket;
108 nextbucket = bucketptr->next;
109 (*free_data) (bucketptr->data);
110 free((char *) bucketptr);
111 bucketptr = nextbucket;
119 * This routine re-initializes the hash table. It frees all the allocated
120 * memory and resets all bucket pointers to NULL.
124 hash_Reset(hashtable, free_data)
126 hash_freefp free_data;
128 hash_member **bucketptr;
131 bucketptr = hashtable->table;
132 for (i = 0; i < hashtable->size; i++) {
133 hashi_FreeMembers(*bucketptr, free_data);
136 hashtable->bucketnum = 0;
137 hashtable->member = (hashtable->table)[0];
143 * Generic hash function to calculate a hash code from the given string.
145 * For each byte of the string, this function left-shifts the value in an
146 * accumulator and then adds the byte into the accumulator. The contents of
147 * the accumulator is returned after the entire string has been processed.
148 * It is assumed that this result will be used as the "hashcode" parameter in
149 * calls to other functions in this package. These functions automatically
150 * adjust the hashcode for the size of each hashtable.
152 * This algorithm probably works best when the hash table size is a prime
155 * Hopefully, this function is better than the previous one which returned
156 * the sum of the squares of all the bytes. I'm still open to other
157 * suggestions for a default hash function. The programmer is more than
158 * welcome to supply his/her own hash function as that is one of the design
159 * features of this package.
163 hash_HashFunction(string, len)
164 unsigned char *string;
170 for (; len > 0; len--) {
172 accum += (unsigned) (*string++ & 0xFF);
180 * Returns TRUE if at least one entry for the given key exists; FALSE
185 hash_Exists(hashtable, hashcode, compare, key)
191 hash_member *memberptr;
193 memberptr = (hashtable->table)[hashcode % (hashtable->size)];
195 if ((*compare) (key, memberptr->data)) {
196 return TRUE; /* Entry does exist */
198 memberptr = memberptr->next;
200 return FALSE; /* Entry does not exist */
206 * Insert the data item "element" into the hash table using "hashcode"
207 * to determine the bucket number, and "compare" and "key" to determine
210 * If the insertion is successful 0 is returned. If a matching entry
211 * already exists in the given bucket of the hash table, or some other error
212 * occurs, -1 is returned and the insertion is not done.
216 hash_Insert(hashtable, hashcode, compare, key, element)
220 hash_datum *key, *element;
224 hashcode %= hashtable->size;
225 if (hash_Exists(hashtable, hashcode, compare, key)) {
226 return -1; /* At least one entry already exists */
228 temp = (hash_member *) malloc(sizeof(hash_member));
230 return -1; /* malloc failed! */
232 temp->data = element;
233 temp->next = (hashtable->table)[hashcode];
234 (hashtable->table)[hashcode] = temp;
235 return 0; /* Success */
241 * Delete all data elements which match the given key. If at least one
242 * element is found and the deletion is successful, 0 is returned.
243 * If no matching elements can be found in the hash table, -1 is returned.
247 hash_Delete(hashtable, hashcode, compare, key, free_data)
252 hash_freefp free_data;
254 hash_member *memberptr, *tempptr;
255 hash_member *previous = NULL;
259 hashcode %= hashtable->size;
262 * Delete the first member of the list if it matches. Since this moves
263 * the second member into the first position we have to keep doing this
264 * over and over until it no longer matches.
266 memberptr = (hashtable->table)[hashcode];
267 while (memberptr && (*compare) (key, memberptr->data)) {
268 (hashtable->table)[hashcode] = memberptr->next;
270 * Stop hashi_FreeMembers() from deleting the whole list!
272 memberptr->next = NULL;
273 hashi_FreeMembers(memberptr, free_data);
274 memberptr = (hashtable->table)[hashcode];
279 * Now traverse the rest of the list
282 previous = memberptr;
283 memberptr = memberptr->next;
286 if ((*compare) (key, memberptr->data)) {
288 previous->next = memberptr = memberptr->next;
290 * Put the brakes on hashi_FreeMembers(). . . .
292 tempptr->next = NULL;
293 hashi_FreeMembers(tempptr, free_data);
296 previous = memberptr;
297 memberptr = memberptr->next;
306 * Locate and return the data entry associated with the given key.
308 * If the data entry is found, a pointer to it is returned. Otherwise,
313 hash_Lookup(hashtable, hashcode, compare, key)
319 hash_member *memberptr;
321 memberptr = (hashtable->table)[hashcode % (hashtable->size)];
323 if ((*compare) (key, memberptr->data)) {
324 return (memberptr->data);
326 memberptr = memberptr->next;
334 * Return the next available entry in the hashtable for a linear search
338 hash_NextEntry(hashtable)
342 hash_member *memberptr;
345 * First try to pick up where we left off.
347 memberptr = hashtable->member;
349 hashtable->member = memberptr->next; /* Set up for next call */
350 return memberptr->data; /* Return the data */
353 * We hit the end of a chain, so look through the array of buckets
354 * until we find a new chain (non-empty bucket) or run out of buckets.
356 bucket = hashtable->bucketnum + 1;
357 while ((bucket < hashtable->size) &&
358 !(memberptr = (hashtable->table)[bucket])) {
363 * Check to see if we ran out of buckets.
365 if (bucket >= hashtable->size) {
367 * Reset to top of table for next call.
369 hashtable->bucketnum = 0;
370 hashtable->member = (hashtable->table)[0];
372 * But return end-of-table indication to the caller this time.
377 * Must have found a non-empty bucket.
379 hashtable->bucketnum = bucket;
380 hashtable->member = memberptr->next; /* Set up for next call */
381 return memberptr->data; /* Return the data */
387 * Return the first entry in a hash table for a linear search
391 hash_FirstEntry(hashtable)
394 hashtable->bucketnum = 0;
395 hashtable->member = (hashtable->table)[0];
396 return hash_NextEntry(hashtable);
403 * c-argdecl-indent: 4
404 * c-continued-statement-offset: 4
405 * c-continued-brace-offset: -4