107 lines
3.1 KiB
C
107 lines
3.1 KiB
C
/*
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hash.c -- hash table management
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Copyright (C) 2012-2013 Guus Sliepen <guus@tinc-vpn.org>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "system.h"
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#include "hash.h"
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#include "xalloc.h"
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/* Generic hash function */
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static uint32_t hash_function(const void *p, size_t len) {
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const uint8_t *q = p;
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uint32_t hash = 0;
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while(true) {
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for(int i = len > 4 ? 4 : len; --i;)
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hash += q[len - i] << (8 * i);
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hash *= 0x9e370001UL; // Golden ratio prime.
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if(len <= 4)
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break;
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len -= 4;
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}
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return hash;
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}
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/* Map 32 bits int onto 0..n-1, without throwing away too many bits if n is 2^8 or 2^16 */
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static uint32_t modulo(uint32_t hash, size_t n) {
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if(n == 0x100)
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return (hash >> 24) ^ ((hash >> 16) & 0xff) ^ ((hash >> 8) & 0xff) ^ (hash & 0xff);
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else if(n == 0x10000)
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return (hash >> 16) ^ (hash & 0xffff);
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else
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return hash % n;
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}
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/* (De)allocation */
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hash_t *hash_alloc(size_t n, size_t size) {
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hash_t *hash = xzalloc(sizeof *hash);
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hash->n = n;
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hash->size = size;
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hash->keys = xzalloc(hash->n * hash->size);
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hash->values = xzalloc(hash->n * sizeof *hash->values);
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return hash;
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}
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void hash_free(hash_t *hash) {
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free(hash->keys);
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free(hash->values);
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free(hash);
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}
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/* Searching and inserting */
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void hash_insert(hash_t *hash, const void *key, const void *value) {
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uint32_t i = modulo(hash_function(key, hash->size), hash->n);
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memcpy(hash->keys + i * hash->size, key, hash->size);
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hash->values[i] = value;
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}
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void *hash_search(const hash_t *hash, const void *key) {
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uint32_t i = modulo(hash_function(key, hash->size), hash->n);
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if(hash->values[i] && !memcmp(key, hash->keys + i * hash->size, hash->size)) {
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return (void *)hash->values[i];
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}
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return NULL;
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}
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void *hash_search_or_insert(hash_t *hash, const void *key, const void *value) {
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uint32_t i = modulo(hash_function(key, hash->size), hash->n);
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if(hash->values[i] && !memcmp(key, hash->keys + i * hash->size, hash->size))
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return (void *)hash->values[i];
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memcpy(hash->keys + i * hash->size, key, hash->size);
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hash->values[i] = value;
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return NULL;
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}
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/* Utility functions */
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void hash_clear(hash_t *hash) {
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memset(hash->values, 0, hash->n * sizeof *hash->values);
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}
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void hash_resize(hash_t *hash, size_t n) {
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hash->keys = xrealloc(hash->keys, n * hash->size);
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hash->values = xrealloc(hash->values, n * sizeof *hash->values);
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if(n > hash->n) {
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memset(hash->keys + hash->n * hash->size, 0, (n - hash->n) * hash->size);
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memset(hash->values + hash->n, 0, (n - hash->n) * sizeof *hash->values);
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}
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}
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