libexec/bootpd/hash.c

/************************************************************************
          Copyright 1988, 1991 by Carnegie Mellon University

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DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
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	$FreeBSD: head/libexec/bootpd/hash.c 21673 1997-01-14 07:20:47Z jkh $

************************************************************************/

/*
 * Generalized hash table ADT
 *
 * Provides multiple, dynamically-allocated, variable-sized hash tables on
 * various data and keys.
 *
 * This package attempts to follow some of the coding conventions suggested
 * by Bob Sidebotham and the AFS Clean Code Committee of the
 * Information Technology Center at Carnegie Mellon.
 */


#include <sys/types.h>
#include <stdlib.h>

#ifndef USE_BFUNCS
#include <memory.h>
/* Yes, memcpy is OK here (no overlapped copies). */
#define bcopy(a,b,c)    memcpy(b,a,c)
#define bzero(p,l)      memset(p,0,l)
#define bcmp(a,b,c)     memcmp(a,b,c)
#endif

#include "hash.h"

#define TRUE		1
#define FALSE		0
#ifndef	NULL
#define NULL		0
#endif

/*
 * This can be changed to make internal routines visible to debuggers, etc.
 */
#ifndef PRIVATE
#define PRIVATE static
#endif

#ifdef	__STDC__
#define P(args) args
#else
#define P(args) ()
#endif

PRIVATE void hashi_FreeMembers P((hash_member *, hash_freefp));

#undef P


/*
 * Hash table initialization routine.
 *
 * This routine creates and intializes a hash table of size "tablesize"
 * entries.  Successful calls return a pointer to the hash table (which must
 * be passed to other hash routines to identify the hash table).  Failed
 * calls return NULL.
 */

hash_tbl *
hash_Init(tablesize)
	unsigned tablesize;
{
	register hash_tbl *hashtblptr;
	register unsigned totalsize;

	if (tablesize > 0) {
		totalsize = sizeof(hash_tbl)
			+ sizeof(hash_member *) * (tablesize - 1);
		hashtblptr = (hash_tbl *) malloc(totalsize);
		if (hashtblptr) {
			bzero((char *) hashtblptr, totalsize);
			hashtblptr->size = tablesize;	/* Success! */
			hashtblptr->bucketnum = 0;
			hashtblptr->member = (hashtblptr->table)[0];
		}
	} else {
		hashtblptr = NULL;		/* Disallow zero-length tables */
	}
	return hashtblptr;			/* NULL if failure */
}


/*
 * Frees an entire linked list of bucket members (used in the open
 * hashing scheme).  Does nothing if the passed pointer is NULL.
 */

PRIVATE void
hashi_FreeMembers(bucketptr, free_data)
	hash_member *bucketptr;
	hash_freefp free_data;
{
	hash_member *nextbucket;
	while (bucketptr) {
		nextbucket = bucketptr->next;
		(*free_data) (bucketptr->data);
		free((char *) bucketptr);
		bucketptr = nextbucket;
	}
}


/*
 * This routine re-initializes the hash table.  It frees all the allocated
 * memory and resets all bucket pointers to NULL.
 */

void
hash_Reset(hashtable, free_data)
	hash_tbl *hashtable;
	hash_freefp free_data;
{
	hash_member **bucketptr;
	unsigned i;

	bucketptr = hashtable->table;
	for (i = 0; i < hashtable->size; i++) {
		hashi_FreeMembers(*bucketptr, free_data);
		*bucketptr++ = NULL;
	}
	hashtable->bucketnum = 0;
	hashtable->member = (hashtable->table)[0];
}


/*
 * Generic hash function to calculate a hash code from the given string.
 *
 * For each byte of the string, this function left-shifts the value in an
 * accumulator and then adds the byte into the accumulator.  The contents of
 * the accumulator is returned after the entire string has been processed.
 * It is assumed that this result will be used as the "hashcode" parameter in
 * calls to other functions in this package.  These functions automatically
 * adjust the hashcode for the size of each hashtable.
 *
 * This algorithm probably works best when the hash table size is a prime
 * number.
 *
 * Hopefully, this function is better than the previous one which returned
 * the sum of the squares of all the bytes.  I'm still open to other
 * suggestions for a default hash function.  The programmer is more than
 * welcome to supply his/her own hash function as that is one of the design
 * features of this package.
 */

unsigned
hash_HashFunction(string, len)
	unsigned char *string;
	register unsigned len;
{
	register unsigned accum;

	accum = 0;
	for (; len > 0; len--) {
		accum <<= 1;
		accum += (unsigned) (*string++ & 0xFF);
	}
	return accum;
}


/*
 * Returns TRUE if at least one entry for the given key exists; FALSE
 * otherwise.
 */

int
hash_Exists(hashtable, hashcode, compare, key)
	hash_tbl *hashtable;
	unsigned hashcode;
	hash_cmpfp compare;
	hash_datum *key;
{
	register hash_member *memberptr;

	memberptr = (hashtable->table)[hashcode % (hashtable->size)];
	while (memberptr) {
		if ((*compare) (key, memberptr->data)) {
			return TRUE;		/* Entry does exist */
		}
		memberptr = memberptr->next;
	}
	return FALSE;				/* Entry does not exist */
}


/*
 * Insert the data item "element" into the hash table using "hashcode"
 * to determine the bucket number, and "compare" and "key" to determine
 * its uniqueness.
 *
 * If the insertion is successful 0 is returned.  If a matching entry
 * already exists in the given bucket of the hash table, or some other error
 * occurs, -1 is returned and the insertion is not done.
 */

int
hash_Insert(hashtable, hashcode, compare, key, element)
	hash_tbl *hashtable;
	unsigned hashcode;
	hash_cmpfp compare;
	hash_datum *key, *element;
{
	hash_member *temp;

	hashcode %= hashtable->size;
	if (hash_Exists(hashtable, hashcode, compare, key)) {
		return -1;				/* At least one entry already exists */
	}
	temp = (hash_member *) malloc(sizeof(hash_member));
	if (!temp)
		return -1;				/* malloc failed! */

	temp->data = element;
	temp->next = (hashtable->table)[hashcode];
	(hashtable->table)[hashcode] = temp;
	return 0;					/* Success */
}


/*
 * Delete all data elements which match the given key.  If at least one
 * element is found and the deletion is successful, 0 is returned.
 * If no matching elements can be found in the hash table, -1 is returned.
 */

int
hash_Delete(hashtable, hashcode, compare, key, free_data)
	hash_tbl *hashtable;
	unsigned hashcode;
	hash_cmpfp compare;
	hash_datum *key;
	hash_freefp free_data;
{
	hash_member *memberptr, *tempptr;
	hash_member *previous = NULL;
	int retval;

	retval = -1;
	hashcode %= hashtable->size;

	/*
	 * Delete the first member of the list if it matches.  Since this moves
	 * the second member into the first position we have to keep doing this
	 * over and over until it no longer matches.
	 */
	memberptr = (hashtable->table)[hashcode];
	while (memberptr && (*compare) (key, memberptr->data)) {
		(hashtable->table)[hashcode] = memberptr->next;
		/*
		 * Stop hashi_FreeMembers() from deleting the whole list!
		 */
		memberptr->next = NULL;
		hashi_FreeMembers(memberptr, free_data);
		memberptr = (hashtable->table)[hashcode];
		retval = 0;
	}

	/*
	 * Now traverse the rest of the list
	 */
	if (memberptr) {
		previous = memberptr;
		memberptr = memberptr->next;
	}
	while (memberptr) {
		if ((*compare) (key, memberptr->data)) {
			tempptr = memberptr;
			previous->next = memberptr = memberptr->next;
			/*
			 * Put the brakes on hashi_FreeMembers(). . . .
			 */
			tempptr->next = NULL;
			hashi_FreeMembers(tempptr, free_data);
			retval = 0;
		} else {
			previous = memberptr;
			memberptr = memberptr->next;
		}
	}
	return retval;
}


/*
 * Locate and return the data entry associated with the given key.
 *
 * If the data entry is found, a pointer to it is returned.  Otherwise,
 * NULL is returned.
 */

hash_datum *
hash_Lookup(hashtable, hashcode, compare, key)
	hash_tbl *hashtable;
	unsigned hashcode;
	hash_cmpfp compare;
	hash_datum *key;
{
	hash_member *memberptr;

	memberptr = (hashtable->table)[hashcode % (hashtable->size)];
	while (memberptr) {
		if ((*compare) (key, memberptr->data)) {
			return (memberptr->data);
		}
		memberptr = memberptr->next;
	}
	return NULL;
}


/*
 * Return the next available entry in the hashtable for a linear search
 */

hash_datum *
hash_NextEntry(hashtable)
	hash_tbl *hashtable;
{
	register unsigned bucket;
	register hash_member *memberptr;

	/*
	 * First try to pick up where we left off.
	 */
	memberptr = hashtable->member;
	if (memberptr) {
		hashtable->member = memberptr->next;	/* Set up for next call */
		return memberptr->data;	/* Return the data */
	}
	/*
	 * We hit the end of a chain, so look through the array of buckets
	 * until we find a new chain (non-empty bucket) or run out of buckets.
	 */
	bucket = hashtable->bucketnum + 1;
	while ((bucket < hashtable->size) &&
		   !(memberptr = (hashtable->table)[bucket])) {
		bucket++;
	}

	/*
	 * Check to see if we ran out of buckets.
	 */
	if (bucket >= hashtable->size) {
		/*
		 * Reset to top of table for next call.
		 */
		hashtable->bucketnum = 0;
		hashtable->member = (hashtable->table)[0];
		/*
		 * But return end-of-table indication to the caller this time.
		 */
		return NULL;
	}
	/*
	 * Must have found a non-empty bucket.
	 */
	hashtable->bucketnum = bucket;
	hashtable->member = memberptr->next;	/* Set up for next call */
	return memberptr->data;		/* Return the data */
}


/*
 * Return the first entry in a hash table for a linear search
 */

hash_datum *
hash_FirstEntry(hashtable)
	hash_tbl *hashtable;
{
	hashtable->bucketnum = 0;
	hashtable->member = (hashtable->table)[0];
	return hash_NextEntry(hashtable);
}

/*
 * Local Variables:
 * tab-width: 4
 * c-indent-level: 4
 * c-argdecl-indent: 4
 * c-continued-statement-offset: 4
 * c-continued-brace-offset: -4
 * c-label-offset: -4
 * c-brace-offset: 0
 * End:
 */