hashtable.c

   1 /*
   2  * Routines to provide a memory-efficient hashtable.
   3  *
   4  * Copyright (C) 2007 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
  45         return tbl;
  46 }
  47
  48 void hashtable_destroy(struct hashtable *tbl)
  49 {
  50         free(tbl->nodes);
  51         free(tbl);
  52 }
  53
  54 /* This returns the node for the indicated key, either newly created or
  55  * already existing.  Returns NULL if not allocating and not found. */
  56 void *hashtable_find(struct hashtable *tbl, int64 key, int allocate_if_missing)
  57 {
  58         int key64 = (tbl->node_size > sizeof (struct ht_int32_node));
  59         struct ht_int32_node *node;
  60         uint32 ndx;
  61
  62         if (allocate_if_missing && tbl->entries > HASH_LOAD_LIMIT(tbl->size)) {
  63                 void *old_nodes = tbl->nodes;
  64                 int size = tbl->size * 2;
  65                 int i;
  66
  67                 if (!(tbl->nodes = new_array0(char, size * tbl->node_size)))
  68                         out_of_memory("hashtable_node");
  69                 tbl->size = size;
  70                 tbl->entries = 0;
  71
  72                 for (i = size / 2; i-- > 0; ) {
  73                         struct ht_int32_node *move_node = HT_NODE(tbl, old_nodes, i);
  74                         int64 move_key = HT_KEY(move_node, key64);
  75                         if (move_key == 0)
  76                                 continue;
  77                         node = hashtable_find(tbl, move_key, 1);
  78                         node->data = move_node->data;
  79                 }
  80
  81                 free(old_nodes);
  82         }
  83
  84         if (!key64) {
  85                 /* Based on Jenkins One-at-a-time hash. */
  86                 uchar buf[4], *keyp = buf;
  87                 int i;
  88
  89                 SIVAL(buf, 0, key);
  90                 for (ndx = 0, i = 0; i < 4; i++) {
  91                         ndx += keyp[i];
  92                         ndx += (ndx << 10);
  93                         ndx ^= (ndx >> 6);
  94                 }
  95                 ndx += (ndx << 3);
  96                 ndx ^= (ndx >> 11);
  97                 ndx += (ndx << 15);
  98         } else {
  99                 /* Based on Jenkins hashword() from lookup3.c. */
 100                 uint32 a, b, c;
 101
 102                 /* Set up the internal state */
 103                 a = b = c = 0xdeadbeef + (8 << 2);
 104
 105 #define rot(x,k) (((x)<<(k)) ^ ((x)>>(32-(k))))
 106                 b += (uint32)(key >> 32);
 107                 a += (uint32)key;
 108                 c ^= b; c -= rot(b, 14);
 109                 a ^= c; a -= rot(c, 11);
 110                 b ^= a; b -= rot(a, 25);
 111                 c ^= b; c -= rot(b, 16);
 112                 a ^= c; a -= rot(c, 4);
 113                 b ^= a; b -= rot(a, 14);
 114                 c ^= b; c -= rot(b, 24);
 115 #undef rot
 116                 ndx = c;
 117         }
 118
 119         /* If it already exists, return the node.  If we're not
 120          * allocating, return NULL if the key is not found. */
 121         while (1) {
 122                 int64 nkey;
 123
 124                 ndx &= tbl->size - 1;
 125                 node = HT_NODE(tbl, tbl->nodes, ndx);
 126                 nkey = HT_KEY(node, key64);
 127
 128                 if (nkey == key)
 129                         return node;
 130                 if (nkey == 0) {
 131                         if (!allocate_if_missing)
 132                                 return NULL;
 133                         break;
 134                 }
 135                 ndx++;
 136         }
 137
 138         /* Take over this empty spot and then return the node. */
 139         if (key64)
 140                 ((struct ht_int64_node*)node)->key = key;
 141         else
 142                 node->key = key;
 143         tbl->entries++;
 144         return node;
 145 }