mdw@git.distorted.org.uk Git - mLib/blob - struct/hash.c

   1 /* -*-c-*-
   2  *
   3  * General hashtable infrastructure
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the mLib utilities library.
  11  *
  12  * mLib is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * mLib is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with mLib; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include <stdio.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33
  34 #include "alloc.h"
  35 #include "arena.h"
  36 #include "bits.h"
  37 #include "exc.h"
  38 #include "hash.h"
  39
  40 /*----- Main code ---------------------------------------------------------*/
  41
  42 /* --- @hash_create@ --- *
  43  *
  44  * Arguments:   @hash_table *t@ = pointer to hashtable to initialize
  45  *              @size_t n@ = number of bins to allocate (zero initially)
  46  *
  47  * Returns:     ---
  48  *
  49  * Use:         Initializes a hashtable with a given number of bins.  The
  50  *              bins are initially empty.  The number of bins must be a power
  51  *              of two.  This is not checked.
  52  */
  53
  54 void hash_create(hash_table *t, size_t n)
  55 {
  56   hash_base **v;
  57
  58   t->a = arena_global;
  59   t->v = x_alloc(t->a, n * sizeof(hash_base *));
  60   t->mask = n - 1;
  61   for (v = t->v; n; v++, n--)
  62     *v = 0;
  63 }
  64
  65 /* --- @hash_destroy@ --- *
  66  *
  67  * Arguments:   @hash_table *t@ = pointer to hashtable to destroy
  68  *
  69  * Returns:     ---
  70  *
  71  * Use:         Frees a hashtable.  The items are not freed: they are the
  72  *              responsibility of the implementation.
  73  */
  74
  75 void hash_destroy(hash_table *t) { x_free(t->a, t->v); }
  76
  77 /* --- @hash_bin@ --- *
  78  *
  79  * Arguments:   @hash_table *t@ = pointer to hashtable
  80  *              @uint32 hash@ = hash value to look up
  81  *
  82  * Returns:     Pointer to the bin's list head.
  83  *
  84  * Use:         Given a hash value return the address of the appropriate list
  85  *              head.  It is safe to remove the current entry from the table.
  86  */
  87
  88 hash_base **hash_bin(hash_table *t, uint32 hash)
  89   { return (HASH_BIN(t, hash)); }
  90
  91 /* --- @hash_extend@ --- *
  92  *
  93  * Arguments:   @hash_table *t@ = pointer to hashtable to extend
  94  *
  95  * Returns:     Nonzero if extension was successful.
  96  *
  97  * Use:         Extends a hashtable.  The number of bins is doubled and the
  98  *              entries are redistributed.
  99  */
 100
 101 int hash_extend(hash_table *t)
 102 {
 103   hash_base **v;
 104   uint32 m = t->mask + 1;
 105   size_t i;
 106
 107   /* --- Allocate a new hash bin vector --- */
 108
 109   if ((v = A_REALLOC(t->a, t->v,
 110                      2 * m * sizeof(hash_base *),
 111                      m * sizeof(hash_base *))) == 0) {
 112     return (0);
 113   }
 114   t->v = v;
 115   t->mask = (m * 2) - 1;
 116
 117   /* --- Wander through the table rehashing things --- */
 118
 119   for (i = 0; i < m; i++) {
 120     hash_base **p = v + i;
 121     hash_base **q = p + m;
 122
 123     while (*p) {
 124       if (!((*p)->hash & m))
 125         p = &(*p)->next;
 126       else {
 127         *q = *p;
 128         q = &(*q)->next;
 129         *p = (*p)->next;
 130       }
 131     }
 132     *p = 0;
 133     *q = 0;
 134   }
 135
 136   return (1);
 137 }
 138
 139 /* --- @hash_remove@ --- *
 140  *
 141  * Arguments:   @hash_table *t@ = pointer to hashtable
 142  *              @hash_base *p@ = pointer to item to remove
 143  *
 144  * Returns:     ---
 145  *
 146  * Use:         Removes an item from a hashtable.  The item itself is not
 147  *              freed, although it is removed from the data structure and is
 148  *              safe to free.
 149  */
 150
 151 void hash_remove(hash_table *t, hash_base *p)
 152 {
 153   hash_base **b = HASH_BIN(t, p->hash);
 154   while (*b) {
 155     if (*b == p) {
 156       *b = p->next;
 157       return;
 158     }
 159     b = &(*b)->next;
 160   }
 161   return;
 162 }
 163
 164 /* --- @hash_mkiter@ --- *
 165  *
 166  * Arguments:   @hash_iter *i@ = pointer to iterator to create
 167  *              @hash_table *t@ = pointer to hashtable to iterate
 168  *
 169  * Returns:     ---
 170  *
 171  * Use:         Initializes a hashtable iterator.
 172  */
 173
 174 void hash_mkiter(hash_iter *i, hash_table *t) { HASH_MKITER(i, t); }
 175
 176 /* --- @hash_next@ --- *
 177  *
 178  * Arguments:   @hash_iter *i@ = pointer to iterator
 179  *
 180  * Returns:     Pointer to the next hashtable entry found, or null.
 181  *
 182  * Use:         Returns the next entry from the hashtable.
 183  */
 184
 185 hash_base *hash_next(hash_iter *i)
 186 {
 187   hash_base *b;
 188   HASH_NEXT(i, b);
 189   return (b);
 190 }
 191
 192 /*----- That's all, folks -------------------------------------------------*/