chiark / gitweb /
Add global unihash table; use universal hashing instead of CRC.
[mLib] / hash.h
CommitLineData
03d53b73 1/* -*-c-*-
2 *
20eb516f 3 * $Id: hash.h,v 1.3 2000/06/17 10:37:39 mdw Exp $
03d53b73 4 *
5 * General hashtable infrastructure
6 *
7 * (c) 1999 Straylight/Edgeware
8 */
9
10/*----- Licensing notice --------------------------------------------------*
11 *
12 * This file is part of the mLib utilities library.
13 *
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.
18 *
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.
23 *
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,
27 * MA 02111-1307, USA.
28 */
29
30/*----- Revision history --------------------------------------------------*
31 *
32 * $Log: hash.h,v $
20eb516f 33 * Revision 1.3 2000/06/17 10:37:39 mdw
34 * Add support for arena management.
35 *
c6e0eaf0 36 * Revision 1.2 1999/12/10 23:42:04 mdw
37 * Change header file guard names.
38 *
03d53b73 39 * Revision 1.1 1999/08/02 14:45:48 mdw
40 * Break low-level hashtable code out from sym.
41 *
42 */
43
c6e0eaf0 44#ifndef MLIB_HASH_H
45#define MLIB_HASH_H
03d53b73 46
47#ifdef __cplusplus
48 extern "C" {
49#endif
50
51/*----- Notes -------------------------------------------------------------*
52 *
53 * This isn't a complete implementation of anything. It's a collection of
54 * useful types and functions which will help when building hashtables of
55 * things. The general-purpose hashtable is provided by the @sym@ functions.
56 */
57
58/*----- Header files ------------------------------------------------------*/
59
60#include <stddef.h>
61
20eb516f 62#ifndef MLIB_ARENA_H
63# include "arena.h"
64#endif
65
c6e0eaf0 66#ifndef MLIB_BITS_H
03d53b73 67# include "bits.h"
68#endif
69
70/*----- Data structures ---------------------------------------------------*/
71
72/* --- Hashtable basics --- *
73 *
74 * This contains the bare minimum to actually get anything useful done. In
75 * particular it doesn't maintain any weighting information: when to extend
76 * the table is left up to the particular implementation.
77 */
78
79typedef struct hash_table {
80 uint32 mask; /* Bit mask of hash bits */
81 struct hash_base **v; /* Vector of hash bins */
20eb516f 82 arena *a; /* Allocation arena */
03d53b73 83} hash_table;
84
85/* --- A hashtable entry --- *
86 *
87 * This is the bare minimum of what needs to be remembered in each hashtable
88 * entry. Comparison of elements is left to the implementation, so I don't
89 * need to know anything about how to represent hash keys here.
90 */
91
92typedef struct hash_base {
93 struct hash_base *next; /* Next entry in hash bin */
94 uint32 hash; /* Hash value for this entry */
95} hash_base;
96
97/* --- A hashtable iterator --- */
98
99typedef struct hash_iter {
100 hash_table *t; /* Hashtable being iterated */
101 hash_base *p; /* Address of next item to return */
102 size_t i; /* Index of next hash bin to use */
103} hash_iter;
104
105/*----- Functions provided ------------------------------------------------*/
106
107/* --- @hash_create@ --- *
108 *
109 * Arguments: @hash_table *t@ = pointer to hashtable to initialize
110 * @size_t n@ = number of bins to allocate (zero initially)
111 *
112 * Returns: ---
113 *
114 * Use: Initializes a hashtable with a given number of bins. The
115 * bins are initially empty. The number of bins must be a power
116 * of two. This is not checked.
117 */
118
119extern void hash_create(hash_table */*t*/, size_t /*n*/);
120
121/* --- @hash_destroy@ --- *
122 *
123 * Arguments: @hash_table *t@ = pointer to hashtable to destroy
124 *
125 * Returns: ---
126 *
127 * Use: Frees a hashtable. The items are not freed: they are the
128 * responsibility of the implementation.
129 */
130
131extern void hash_destroy(hash_table */*t*/);
132
133/* --- @hash_bin@ --- *
134 *
135 * Arguments: @hash_table *t@ = pointer to hashtable
136 * @uint32 hash@ = hash value to look up
137 *
138 * Returns: Pointer to the bin's list head.
139 *
140 * Use: Given a hash value return the address of the appropriate list
141 * head. It is safe to remove the current entry from the table.
142 */
143
144#define HASH_BIN(t, hash) ((t)->v + ((hash) & (t)->mask))
145
146extern hash_base **hash_bin(hash_table */*t*/, uint32 /*hash*/);
147
148/* --- @hash_extend@ --- *
149 *
150 * Arguments: @hash_table *t@ = pointer to hashtable to extend
151 *
152 * Returns: Nonzero if extension was successful.
153 *
154 * Use: Extends a hashtable. The number of bins is doubled and the
155 * entries are redistributed.
156 */
157
158extern int hash_extend(hash_table */*t*/);
159
160/* --- @hash_remove@ --- *
161 *
162 * Arguments: @hash_table *t@ = pointer to hashtable
163 * @hash_base *p@ = pointer to item to remove
164 *
165 * Returns: ---
166 *
167 * Use: Removes an item from a hashtable. The item itself is not
168 * freed, although it is removed from the data structure and is
169 * safe to free.
170 */
171
172extern void hash_remove(hash_table */*t*/, hash_base */*p*/);
173
174/* --- @hash_mkiter@ --- *
175 *
176 * Arguments: @hash_iter *i@ = pointer to iterator to create
177 * @hash_table *t@ = pointer to hashtable to iterate
178 *
179 * Returns: ---
180 *
181 * Use: Initializes a hashtable iterator.
182 */
183
184#define HASH_MKITER(i_, t_) ((i_)->t = (t_), (i_)->p = 0, (i_)->i = 0)
185
186extern void hash_mkiter(hash_iter */*i*/, hash_table */*t*/);
187
188/* --- @hash_next@ --- *
189 *
190 * Arguments: @hash_iter *i@ = pointer to iterator
191 *
192 * Returns: Pointer to the next hashtable entry found, or null.
193 *
194 * Use: Returns the next entry from the hashtable.
195 */
196
197#define HASH_NEXT(i_, b_) do { \
198 hash_iter *_i = (i_); \
199 hash_base *_p; \
200 hash_table *_t = _i->t; \
201 uint32 _m = _t->mask; \
202 \
203 for (;;) { \
204 if (_i->p) { \
205 _p = _i->p; \
206 _i->p = _p->next; \
207 break; \
208 } else if (_i->i > _m) { \
209 _p = 0; \
210 break; \
211 } else \
212 _i->p = _t->v[_i->i++]; \
213 } \
214 (b_) = _p; \
215} while (0)
216
217extern hash_base *hash_next(hash_iter */*i*/);
218
219/*----- That's all, folks -------------------------------------------------*/
220
221#ifdef __cplusplus
222 }
223#endif
224
225#endif