3 * $Id: hash.h,v 1.2 1999/12/10 23:42:04 mdw Exp $
5 * General hashtable infrastructure
7 * (c) 1999 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of the mLib utilities library.
14 * mLib is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU Library General Public License as
16 * published by the Free Software Foundation; either version 2 of the
17 * License, or (at your option) any later version.
19 * mLib is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU Library General Public License for more details.
24 * You should have received a copy of the GNU Library General Public
25 * License along with mLib; if not, write to the Free
26 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
30 /*----- Revision history --------------------------------------------------*
33 * Revision 1.2 1999/12/10 23:42:04 mdw
34 * Change header file guard names.
36 * Revision 1.1 1999/08/02 14:45:48 mdw
37 * Break low-level hashtable code out from sym.
48 /*----- Notes -------------------------------------------------------------*
50 * This isn't a complete implementation of anything. It's a collection of
51 * useful types and functions which will help when building hashtables of
52 * things. The general-purpose hashtable is provided by the @sym@ functions.
55 /*----- Header files ------------------------------------------------------*/
63 /*----- Data structures ---------------------------------------------------*/
65 /* --- Hashtable basics --- *
67 * This contains the bare minimum to actually get anything useful done. In
68 * particular it doesn't maintain any weighting information: when to extend
69 * the table is left up to the particular implementation.
72 typedef struct hash_table {
73 uint32 mask; /* Bit mask of hash bits */
74 struct hash_base **v; /* Vector of hash bins */
77 /* --- A hashtable entry --- *
79 * This is the bare minimum of what needs to be remembered in each hashtable
80 * entry. Comparison of elements is left to the implementation, so I don't
81 * need to know anything about how to represent hash keys here.
84 typedef struct hash_base {
85 struct hash_base *next; /* Next entry in hash bin */
86 uint32 hash; /* Hash value for this entry */
89 /* --- A hashtable iterator --- */
91 typedef struct hash_iter {
92 hash_table *t; /* Hashtable being iterated */
93 hash_base *p; /* Address of next item to return */
94 size_t i; /* Index of next hash bin to use */
97 /*----- Functions provided ------------------------------------------------*/
99 /* --- @hash_create@ --- *
101 * Arguments: @hash_table *t@ = pointer to hashtable to initialize
102 * @size_t n@ = number of bins to allocate (zero initially)
106 * Use: Initializes a hashtable with a given number of bins. The
107 * bins are initially empty. The number of bins must be a power
108 * of two. This is not checked.
111 extern void hash_create(hash_table */*t*/, size_t /*n*/);
113 /* --- @hash_destroy@ --- *
115 * Arguments: @hash_table *t@ = pointer to hashtable to destroy
119 * Use: Frees a hashtable. The items are not freed: they are the
120 * responsibility of the implementation.
123 extern void hash_destroy(hash_table */*t*/);
125 /* --- @hash_bin@ --- *
127 * Arguments: @hash_table *t@ = pointer to hashtable
128 * @uint32 hash@ = hash value to look up
130 * Returns: Pointer to the bin's list head.
132 * Use: Given a hash value return the address of the appropriate list
133 * head. It is safe to remove the current entry from the table.
136 #define HASH_BIN(t, hash) ((t)->v + ((hash) & (t)->mask))
138 extern hash_base **hash_bin(hash_table */*t*/, uint32 /*hash*/);
140 /* --- @hash_extend@ --- *
142 * Arguments: @hash_table *t@ = pointer to hashtable to extend
144 * Returns: Nonzero if extension was successful.
146 * Use: Extends a hashtable. The number of bins is doubled and the
147 * entries are redistributed.
150 extern int hash_extend(hash_table */*t*/);
152 /* --- @hash_remove@ --- *
154 * Arguments: @hash_table *t@ = pointer to hashtable
155 * @hash_base *p@ = pointer to item to remove
159 * Use: Removes an item from a hashtable. The item itself is not
160 * freed, although it is removed from the data structure and is
164 extern void hash_remove(hash_table */*t*/, hash_base */*p*/);
166 /* --- @hash_mkiter@ --- *
168 * Arguments: @hash_iter *i@ = pointer to iterator to create
169 * @hash_table *t@ = pointer to hashtable to iterate
173 * Use: Initializes a hashtable iterator.
176 #define HASH_MKITER(i_, t_) ((i_)->t = (t_), (i_)->p = 0, (i_)->i = 0)
178 extern void hash_mkiter(hash_iter */*i*/, hash_table */*t*/);
180 /* --- @hash_next@ --- *
182 * Arguments: @hash_iter *i@ = pointer to iterator
184 * Returns: Pointer to the next hashtable entry found, or null.
186 * Use: Returns the next entry from the hashtable.
189 #define HASH_NEXT(i_, b_) do { \
190 hash_iter *_i = (i_); \
192 hash_table *_t = _i->t; \
193 uint32 _m = _t->mask; \
200 } else if (_i->i > _m) { \
204 _i->p = _t->v[_i->i++]; \
209 extern hash_base *hash_next(hash_iter */*i*/);
211 /*----- That's all, folks -------------------------------------------------*/