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