hashtable.c

   1 /*
   2  * Routines to provide a memory-efficient hashtable.
   3  *
   4  * Copyright (C) 2007-2008 Wayne Davison
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License along
  17  * with this program; if not, visit the http://fsf.org website.
  18  */
  19
  20 #include "rsync.h"
  21
  22 #define HASH_LOAD_LIMIT(size) ((size)*3/4)
  23
  24 struct hashtable *hashtable_create(int size, int key64)
  25 {
  26         struct hashtable *tbl;
  27         int node_size = key64 ? sizeof (struct ht_int64_node)
  28                               : sizeof (struct ht_int32_node);
  29
  30         /* Pick a power of 2 that can hold the requested size. */
  31         if (size & (size-1) || size < 16) {
  32                 int req = size;
  33                 size = 16;
  34                 while (size < req)
  35                         size *= 2;
  36         }
  37
  38         if (!(tbl = new(struct hashtable))
  39          || !(tbl->nodes = new_array0(char, size * node_size)))
  40                 out_of_memory("hashtable_create");
  41         tbl->size = size;
  42         tbl->entries = 0;
  43         tbl->node_size = node_size;
  44         tbl->key64 = key64;
  45
  46         return tbl;
  47 }
  48
  49 void hashtable_destroy(struct hashtable *tbl)
  50 {
  51         free(tbl->nodes);
  52         free(tbl);
  53 }
  54
  55 /* This returns the node for the indicated key, either newly created or
  56  * already existing.  Returns NULL if not allocating and not found. */
  57 void *hashtable_find(struct hashtable *tbl, int64 key, int allocate_if_missing)
  58 {
  59         int key64 = tbl->key64;
  60         struct ht_int32_node *node;
  61         uint32 ndx;
  62
  63         if (allocate_if_missing && tbl->entries > HASH_LOAD_LIMIT(tbl->size)) {
  64                 void *old_nodes = tbl->nodes;
  65                 int size = tbl->size * 2;
  66                 int i;
  67
  68                 if (!(tbl->nodes = new_array0(char, size * tbl->node_size)))
  69                         out_of_memory("hashtable_node");
  70                 tbl->size = size;
  71                 tbl->entries = 0;
  72
  73                 for (i = size / 2; i-- > 0; ) {
  74                         struct ht_int32_node *move_node = HT_NODE(tbl, old_nodes, i);
  75                         int64 move_key = HT_KEY(move_node, key64);
  76                         if (move_key == 0)
  77                                 continue;
  78                         node = hashtable_find(tbl, move_key, 1);
  79                         node->data = move_node->data;
  80                 }
  81
  82                 free(old_nodes);
  83         }
  84
  85         if (!key64) {
  86                 /* Based on Jenkins One-at-a-time hash. */
  87                 uchar buf[4], *keyp = buf;
  88                 int i;
  89
  90                 SIVAL(buf, 0, key);
  91                 for (ndx = 0, i = 0; i < 4; i++) {
  92                         ndx += keyp[i];
  93                         ndx += (ndx << 10);
  94                         ndx ^= (ndx >> 6);
  95                 }
  96                 ndx += (ndx << 3);
  97                 ndx ^= (ndx >> 11);
  98                 ndx += (ndx << 15);
  99         } else {
 100                 /* Based on Jenkins hashword() from lookup3.c. */
 101                 uint32 a, b, c;
 102
 103                 /* Set up the internal state */
 104                 a = b = c = 0xdeadbeef + (8 << 2);
 105
 106 #define rot(x,k) (((x)<<(k)) ^ ((x)>>(32-(k))))
 107                 b += (uint32)(key >> 32);
 108                 a += (uint32)key;
 109                 c ^= b; c -= rot(b, 14);
 110                 a ^= c; a -= rot(c, 11);
 111                 b ^= a; b -= rot(a, 25);
 112                 c ^= b; c -= rot(b, 16);
 113                 a ^= c; a -= rot(c, 4);
 114                 b ^= a; b -= rot(a, 14);
 115                 c ^= b; c -= rot(b, 24);
 116 #undef rot
 117                 ndx = c;
 118         }
 119
 120         /* If it already exists, return the node.  If we're not
 121          * allocating, return NULL if the key is not found. */
 122         while (1) {
 123                 int64 nkey;
 124
 125                 ndx &= tbl->size - 1;
 126                 node = HT_NODE(tbl, tbl->nodes, ndx);
 127                 nkey = HT_KEY(node, key64);
 128
 129                 if (nkey == key)
 130                         return node;
 131                 if (nkey == 0) {
 132                         if (!allocate_if_missing)
 133                                 return NULL;
 134                         break;
 135                 }
 136                 ndx++;
 137         }
 138
 139         /* Take over this empty spot and then return the node. */
 140         if (key64)
 141                 ((struct ht_int64_node*)node)->key = key;
 142         else
 143                 node->key = key;
 144         tbl->entries++;
 145         return node;
 146 }