release/src/router/tinc/src/hash.c

   1 /*
   2     hash.c -- hash table management
   3     Copyright (C) 2012-2013 Guus Sliepen <guus@tinc-vpn.org>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License along
  16     with this program; if not, write to the Free Software Foundation, Inc.,
  17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #include "system.h"
  21
  22 #include "hash.h"
  23 #include "xalloc.h"
  24
  25 /* Generic hash function */
  26
  27 static uint32_t hash_function(const void *p, size_t len) {
  28         const uint8_t *q = p;
  29         uint32_t hash = 0;
  30         while(true) {
  31                 for(int i = len > 4 ? 4 : len; --i;)
  32                         hash += q[len - i] << (8 * i);
  33                 hash *= 0x9e370001UL; // Golden ratio prime.
  34                 if(len <= 4)
  35                         break;
  36                 len -= 4;
  37         }
  38         return hash;
  39 }
  40
  41 /* Map 32 bits int onto 0..n-1, without throwing away too many bits if n is 2^8 or 2^16 */
  42
  43 static uint32_t modulo(uint32_t hash, size_t n) {
  44         if(n == 0x100)
  45                 return (hash >> 24) ^ ((hash >> 16) & 0xff) ^ ((hash >> 8) & 0xff) ^ (hash & 0xff);
  46         else if(n == 0x10000)
  47                 return (hash >> 16) ^ (hash & 0xffff);
  48         else
  49                 return hash % n;
  50 }
  51
  52 /* (De)allocation */
  53
  54 hash_t *hash_alloc(size_t n, size_t size) {
  55         hash_t *hash = xzalloc(sizeof *hash);
  56         hash->n = n;
  57         hash->size = size;
  58         hash->keys = xzalloc(hash->n * hash->size);
  59         hash->values = xzalloc(hash->n * sizeof *hash->values);
  60         return hash;
  61 }
  62
  63 void hash_free(hash_t *hash) {
  64         free(hash->keys);
  65         free(hash->values);
  66         free(hash);
  67 }
  68
  69 /* Searching and inserting */
  70
  71 void hash_insert(hash_t *hash, const void *key, const void *value) {
  72         uint32_t i = modulo(hash_function(key, hash->size), hash->n);
  73         memcpy(hash->keys + i * hash->size, key, hash->size);
  74         hash->values[i] = value;
  75 }
  76
  77 void *hash_search(const hash_t *hash, const void *key) {
  78         uint32_t i = modulo(hash_function(key, hash->size), hash->n);
  79         if(hash->values[i] && !memcmp(key, hash->keys + i * hash->size, hash->size)) {
  80                 return (void *)hash->values[i];
  81         }
  82         return NULL;
  83 }
  84
  85 void *hash_search_or_insert(hash_t *hash, const void *key, const void *value) {
  86         uint32_t i = modulo(hash_function(key, hash->size), hash->n);
  87         if(hash->values[i] && !memcmp(key, hash->keys + i * hash->size, hash->size))
  88                 return (void *)hash->values[i];
  89         memcpy(hash->keys + i * hash->size, key, hash->size);
  90         hash->values[i] = value;
  91         return NULL;
  92 }
  93
  94 /* Utility functions */
  95
  96 void hash_clear(hash_t *hash) {
  97         memset(hash->values, 0, hash->n * sizeof *hash->values);
  98 }
  99
 100 void hash_resize(hash_t *hash, size_t n) {
 101         hash->keys = xrealloc(hash->keys, n * hash->size);
 102         hash->values = xrealloc(hash->values, n * sizeof *hash->values);
 103         if(n > hash->n) {
 104                 memset(hash->keys + hash->n * hash->size, 0, (n - hash->n) * hash->size);
 105                 memset(hash->values + hash->n, 0, (n - hash->n) * sizeof *hash->values);
 106         }
 107 }