426 lines
10 KiB
C
426 lines
10 KiB
C
/************************************************************************
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Copyright 1988, 1991 by Carnegie Mellon University
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All Rights Reserved
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Permission to use, copy, modify, and distribute this software and its
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documentation for any purpose and without fee is hereby granted, provided
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that the above copyright notice appear in all copies and that both that
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copyright notice and this permission notice appear in supporting
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documentation, and that the name of Carnegie Mellon University not be used
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in advertising or publicity pertaining to distribution of the software
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without specific, written prior permission.
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CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
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SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.
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IN NO EVENT SHALL CMU BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
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DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
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PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
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ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
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SOFTWARE.
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************************************************************************/
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#ifndef lint
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static char rcsid[] = "$Id: hash.c,v 1.2 1994/08/22 22:14:58 gwr Exp $";
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#endif
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/*
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* Generalized hash table ADT
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*
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* Provides multiple, dynamically-allocated, variable-sized hash tables on
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* various data and keys.
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*
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* This package attempts to follow some of the coding conventions suggested
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* by Bob Sidebotham and the AFS Clean Code Committee of the
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* Information Technology Center at Carnegie Mellon.
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*/
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#include <sys/types.h>
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#include <stdlib.h>
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#ifndef USE_BFUNCS
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#include <memory.h>
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/* Yes, memcpy is OK here (no overlapped copies). */
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#define bcopy(a,b,c) memcpy(b,a,c)
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#define bzero(p,l) memset(p,0,l)
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#define bcmp(a,b,c) memcmp(a,b,c)
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#endif
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#include "hash.h"
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#define TRUE 1
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#define FALSE 0
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#ifndef NULL
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#define NULL 0
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#endif
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/*
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* This can be changed to make internal routines visible to debuggers, etc.
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*/
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#ifndef PRIVATE
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#define PRIVATE static
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#endif
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#ifdef __STDC__
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#define P(args) args
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#else
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#define P(args) ()
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#endif
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PRIVATE void hashi_FreeMembers P((hash_member *, hash_freefp));
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#undef P
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/*
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* Hash table initialization routine.
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*
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* This routine creates and intializes a hash table of size "tablesize"
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* entries. Successful calls return a pointer to the hash table (which must
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* be passed to other hash routines to identify the hash table). Failed
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* calls return NULL.
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*/
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hash_tbl *
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hash_Init(tablesize)
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unsigned tablesize;
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{
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register hash_tbl *hashtblptr;
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register unsigned totalsize;
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if (tablesize > 0) {
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totalsize = sizeof(hash_tbl)
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+ sizeof(hash_member *) * (tablesize - 1);
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hashtblptr = (hash_tbl *) malloc(totalsize);
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if (hashtblptr) {
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bzero((char *) hashtblptr, totalsize);
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hashtblptr->size = tablesize; /* Success! */
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hashtblptr->bucketnum = 0;
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hashtblptr->member = (hashtblptr->table)[0];
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}
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} else {
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hashtblptr = NULL; /* Disallow zero-length tables */
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}
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return hashtblptr; /* NULL if failure */
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}
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/*
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* Frees an entire linked list of bucket members (used in the open
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* hashing scheme). Does nothing if the passed pointer is NULL.
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*/
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PRIVATE void
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hashi_FreeMembers(bucketptr, free_data)
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hash_member *bucketptr;
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hash_freefp free_data;
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{
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hash_member *nextbucket;
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while (bucketptr) {
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nextbucket = bucketptr->next;
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(*free_data) (bucketptr->data);
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free((char *) bucketptr);
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bucketptr = nextbucket;
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}
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}
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/*
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* This routine re-initializes the hash table. It frees all the allocated
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* memory and resets all bucket pointers to NULL.
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*/
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void
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hash_Reset(hashtable, free_data)
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hash_tbl *hashtable;
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hash_freefp free_data;
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{
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hash_member **bucketptr;
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unsigned i;
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bucketptr = hashtable->table;
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for (i = 0; i < hashtable->size; i++) {
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hashi_FreeMembers(*bucketptr, free_data);
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*bucketptr++ = NULL;
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}
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hashtable->bucketnum = 0;
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hashtable->member = (hashtable->table)[0];
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}
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/*
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* Generic hash function to calculate a hash code from the given string.
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*
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* For each byte of the string, this function left-shifts the value in an
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* accumulator and then adds the byte into the accumulator. The contents of
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* the accumulator is returned after the entire string has been processed.
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* It is assumed that this result will be used as the "hashcode" parameter in
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* calls to other functions in this package. These functions automatically
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* adjust the hashcode for the size of each hashtable.
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*
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* This algorithm probably works best when the hash table size is a prime
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* number.
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*
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* Hopefully, this function is better than the previous one which returned
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* the sum of the squares of all the bytes. I'm still open to other
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* suggestions for a default hash function. The programmer is more than
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* welcome to supply his/her own hash function as that is one of the design
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* features of this package.
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*/
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unsigned
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hash_HashFunction(string, len)
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unsigned char *string;
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register unsigned len;
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{
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register unsigned accum;
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accum = 0;
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for (; len > 0; len--) {
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accum <<= 1;
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accum += (unsigned) (*string++ & 0xFF);
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}
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return accum;
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}
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/*
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* Returns TRUE if at least one entry for the given key exists; FALSE
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* otherwise.
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*/
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int
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hash_Exists(hashtable, hashcode, compare, key)
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hash_tbl *hashtable;
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unsigned hashcode;
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hash_cmpfp compare;
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hash_datum *key;
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{
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register hash_member *memberptr;
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memberptr = (hashtable->table)[hashcode % (hashtable->size)];
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while (memberptr) {
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if ((*compare) (key, memberptr->data)) {
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return TRUE; /* Entry does exist */
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}
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memberptr = memberptr->next;
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}
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return FALSE; /* Entry does not exist */
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}
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/*
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* Insert the data item "element" into the hash table using "hashcode"
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* to determine the bucket number, and "compare" and "key" to determine
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* its uniqueness.
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*
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* If the insertion is successful 0 is returned. If a matching entry
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* already exists in the given bucket of the hash table, or some other error
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* occurs, -1 is returned and the insertion is not done.
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*/
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int
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hash_Insert(hashtable, hashcode, compare, key, element)
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hash_tbl *hashtable;
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unsigned hashcode;
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hash_cmpfp compare;
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hash_datum *key, *element;
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{
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hash_member *temp;
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hashcode %= hashtable->size;
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if (hash_Exists(hashtable, hashcode, compare, key)) {
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return -1; /* At least one entry already exists */
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}
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temp = (hash_member *) malloc(sizeof(hash_member));
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if (!temp)
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return -1; /* malloc failed! */
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temp->data = element;
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temp->next = (hashtable->table)[hashcode];
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(hashtable->table)[hashcode] = temp;
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return 0; /* Success */
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}
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/*
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* Delete all data elements which match the given key. If at least one
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* element is found and the deletion is successful, 0 is returned.
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* If no matching elements can be found in the hash table, -1 is returned.
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*/
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int
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hash_Delete(hashtable, hashcode, compare, key, free_data)
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hash_tbl *hashtable;
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unsigned hashcode;
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hash_cmpfp compare;
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hash_datum *key;
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hash_freefp free_data;
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{
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hash_member *memberptr, *tempptr;
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hash_member *previous = NULL;
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int retval;
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retval = -1;
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hashcode %= hashtable->size;
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/*
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* Delete the first member of the list if it matches. Since this moves
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* the second member into the first position we have to keep doing this
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* over and over until it no longer matches.
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*/
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memberptr = (hashtable->table)[hashcode];
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while (memberptr && (*compare) (key, memberptr->data)) {
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(hashtable->table)[hashcode] = memberptr->next;
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/*
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* Stop hashi_FreeMembers() from deleting the whole list!
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*/
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memberptr->next = NULL;
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hashi_FreeMembers(memberptr, free_data);
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memberptr = (hashtable->table)[hashcode];
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retval = 0;
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}
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/*
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* Now traverse the rest of the list
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*/
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if (memberptr) {
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previous = memberptr;
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memberptr = memberptr->next;
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}
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while (memberptr) {
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if ((*compare) (key, memberptr->data)) {
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tempptr = memberptr;
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previous->next = memberptr = memberptr->next;
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/*
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* Put the brakes on hashi_FreeMembers(). . . .
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*/
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tempptr->next = NULL;
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hashi_FreeMembers(tempptr, free_data);
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retval = 0;
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} else {
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previous = memberptr;
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memberptr = memberptr->next;
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}
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}
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return retval;
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}
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/*
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* Locate and return the data entry associated with the given key.
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*
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* If the data entry is found, a pointer to it is returned. Otherwise,
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* NULL is returned.
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*/
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hash_datum *
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hash_Lookup(hashtable, hashcode, compare, key)
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hash_tbl *hashtable;
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unsigned hashcode;
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hash_cmpfp compare;
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hash_datum *key;
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{
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hash_member *memberptr;
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memberptr = (hashtable->table)[hashcode % (hashtable->size)];
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while (memberptr) {
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if ((*compare) (key, memberptr->data)) {
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return (memberptr->data);
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}
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memberptr = memberptr->next;
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}
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return NULL;
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}
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/*
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* Return the next available entry in the hashtable for a linear search
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*/
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hash_datum *
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hash_NextEntry(hashtable)
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hash_tbl *hashtable;
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{
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register unsigned bucket;
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register hash_member *memberptr;
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/*
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* First try to pick up where we left off.
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*/
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memberptr = hashtable->member;
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if (memberptr) {
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hashtable->member = memberptr->next; /* Set up for next call */
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return memberptr->data; /* Return the data */
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}
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/*
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* We hit the end of a chain, so look through the array of buckets
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* until we find a new chain (non-empty bucket) or run out of buckets.
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*/
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bucket = hashtable->bucketnum + 1;
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while ((bucket < hashtable->size) &&
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!(memberptr = (hashtable->table)[bucket])) {
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bucket++;
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}
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/*
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* Check to see if we ran out of buckets.
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*/
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if (bucket >= hashtable->size) {
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/*
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* Reset to top of table for next call.
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*/
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hashtable->bucketnum = 0;
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hashtable->member = (hashtable->table)[0];
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/*
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* But return end-of-table indication to the caller this time.
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*/
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return NULL;
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}
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/*
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* Must have found a non-empty bucket.
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*/
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hashtable->bucketnum = bucket;
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hashtable->member = memberptr->next; /* Set up for next call */
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return memberptr->data; /* Return the data */
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}
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/*
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* Return the first entry in a hash table for a linear search
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*/
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hash_datum *
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hash_FirstEntry(hashtable)
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hash_tbl *hashtable;
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{
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hashtable->bucketnum = 0;
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hashtable->member = (hashtable->table)[0];
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return hash_NextEntry(hashtable);
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}
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/*
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* Local Variables:
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* tab-width: 4
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* c-indent-level: 4
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* c-argdecl-indent: 4
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* c-continued-statement-offset: 4
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* c-continued-brace-offset: -4
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* c-label-offset: -4
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* c-brace-offset: 0
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* End:
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*/
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