3 * $Id: hash.h,v 1.4 2004/04/08 01:36:11 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,
37 /*----- Notes -------------------------------------------------------------*
39 * This isn't a complete implementation of anything. It's a collection of
40 * useful types and functions which will help when building hashtables of
41 * things. The general-purpose hashtable is provided by the @sym@ functions.
44 /*----- Header files ------------------------------------------------------*/
56 /*----- Data structures ---------------------------------------------------*/
58 /* --- Hashtable basics --- *
60 * This contains the bare minimum to actually get anything useful done. In
61 * particular it doesn't maintain any weighting information: when to extend
62 * the table is left up to the particular implementation.
65 typedef struct hash_table
{
66 uint32 mask
; /* Bit mask of hash bits */
67 struct hash_base
**v
; /* Vector of hash bins */
68 arena
*a
; /* Allocation arena */
71 /* --- A hashtable entry --- *
73 * This is the bare minimum of what needs to be remembered in each hashtable
74 * entry. Comparison of elements is left to the implementation, so I don't
75 * need to know anything about how to represent hash keys here.
78 typedef struct hash_base
{
79 struct hash_base
*next
; /* Next entry in hash bin */
80 uint32 hash
; /* Hash value for this entry */
83 /* --- A hashtable iterator --- */
85 typedef struct hash_iter
{
86 hash_table
*t
; /* Hashtable being iterated */
87 hash_base
*p
; /* Address of next item to return */
88 size_t i
; /* Index of next hash bin to use */
91 /*----- Functions provided ------------------------------------------------*/
93 /* --- @hash_create@ --- *
95 * Arguments: @hash_table *t@ = pointer to hashtable to initialize
96 * @size_t n@ = number of bins to allocate (zero initially)
100 * Use: Initializes a hashtable with a given number of bins. The
101 * bins are initially empty. The number of bins must be a power
102 * of two. This is not checked.
105 extern void hash_create(hash_table */
*t*/
, size_t /*n*/);
107 /* --- @hash_destroy@ --- *
109 * Arguments: @hash_table *t@ = pointer to hashtable to destroy
113 * Use: Frees a hashtable. The items are not freed: they are the
114 * responsibility of the implementation.
117 extern void hash_destroy(hash_table */
*t*/
);
119 /* --- @hash_bin@ --- *
121 * Arguments: @hash_table *t@ = pointer to hashtable
122 * @uint32 hash@ = hash value to look up
124 * Returns: Pointer to the bin's list head.
126 * Use: Given a hash value return the address of the appropriate list
127 * head. It is safe to remove the current entry from the table.
130 #define HASH_BIN(t, hash) ((t)->v + ((hash) & (t)->mask))
132 extern hash_base
**hash_bin(hash_table */
*t*/
, uint32
/*hash*/);
134 /* --- @hash_extend@ --- *
136 * Arguments: @hash_table *t@ = pointer to hashtable to extend
138 * Returns: Nonzero if extension was successful.
140 * Use: Extends a hashtable. The number of bins is doubled and the
141 * entries are redistributed.
144 extern int hash_extend(hash_table */
*t*/
);
146 /* --- @hash_remove@ --- *
148 * Arguments: @hash_table *t@ = pointer to hashtable
149 * @hash_base *p@ = pointer to item to remove
153 * Use: Removes an item from a hashtable. The item itself is not
154 * freed, although it is removed from the data structure and is
158 extern void hash_remove(hash_table */
*t*/
, hash_base */
*p*/
);
160 /* --- @hash_mkiter@ --- *
162 * Arguments: @hash_iter *i@ = pointer to iterator to create
163 * @hash_table *t@ = pointer to hashtable to iterate
167 * Use: Initializes a hashtable iterator.
170 #define HASH_MKITER(i_, t_) ((i_)->t = (t_), (i_)->p = 0, (i_)->i = 0)
172 extern void hash_mkiter(hash_iter */
*i*/
, hash_table */
*t*/
);
174 /* --- @hash_next@ --- *
176 * Arguments: @hash_iter *i@ = pointer to iterator
178 * Returns: Pointer to the next hashtable entry found, or null.
180 * Use: Returns the next entry from the hashtable.
183 #define HASH_NEXT(i_, b_) do { \
184 hash_iter *_i = (i_); \
186 hash_table *_t = _i->t; \
187 uint32 _m = _t->mask; \
194 } else if (_i->i > _m) { \
198 _i->p = _t->v[_i->i++]; \
203 extern hash_base
*hash_next(hash_iter */
*i*/
);
205 /*----- That's all, folks -------------------------------------------------*/