/* * pkghash.c * * Copyright (c) 2011-2013 Pacman Development Team <pacman-dev@archlinux.org> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ #include <errno.h> #include "pkghash.h" #include "util.h" /* List of primes for possible sizes of hash tables. * * The maximum table size is the last prime under 1,000,000. That is * more than an order of magnitude greater than the number of packages * in any Linux distribution, and well under UINT_MAX. */ static const unsigned int prime_list[] = { 11u, 13u, 17u, 19u, 23u, 29u, 31u, 37u, 41u, 43u, 47u, 53u, 59u, 61u, 67u, 71u, 73u, 79u, 83u, 89u, 97u, 103u, 109u, 113u, 127u, 137u, 139u, 149u, 157u, 167u, 179u, 193u, 199u, 211u, 227u, 241u, 257u, 277u, 293u, 313u, 337u, 359u, 383u, 409u, 439u, 467u, 503u, 541u, 577u, 619u, 661u, 709u, 761u, 823u, 887u, 953u, 1031u, 1109u, 1193u, 1289u, 1381u, 1493u, 1613u, 1741u, 1879u, 2029u, 2179u, 2357u, 2549u, 2753u, 2971u, 3209u, 3469u, 3739u, 4027u, 4349u, 4703u, 5087u, 5503u, 5953u, 6427u, 6949u, 7517u, 8123u, 8783u, 9497u, 10273u, 11113u, 12011u, 12983u, 14033u, 15173u, 16411u, 17749u, 19183u, 20753u, 22447u, 24281u, 26267u, 28411u, 30727u, 33223u, 35933u, 38873u, 42043u, 45481u, 49201u, 53201u, 57557u, 62233u, 67307u, 72817u, 78779u, 85229u, 92203u, 99733u, 107897u, 116731u, 126271u, 136607u, 147793u, 159871u, 172933u, 187091u, 202409u, 218971u, 236897u, 256279u, 277261u, 299951u, 324503u, 351061u, 379787u, 410857u, 444487u, 480881u, 520241u, 562841u, 608903u, 658753u, 712697u, 771049u, 834181u, 902483u, 976369u }; /* How far forward do we look when linear probing for a spot? */ static const unsigned int stride = 1; /* What is the maximum load percentage of our hash table? */ static const double max_hash_load = 0.68; /* Initial load percentage given a certain size */ static const double initial_hash_load = 0.58; /* Allocate a hash table with space for at least "size" elements */ alpm_pkghash_t *_alpm_pkghash_create(unsigned int size) { alpm_pkghash_t *hash = NULL; unsigned int i, loopsize; CALLOC(hash, 1, sizeof(alpm_pkghash_t), return NULL); size = size / initial_hash_load + 1; loopsize = sizeof(prime_list) / sizeof(*prime_list); for(i = 0; i < loopsize; i++) { if(prime_list[i] > size) { hash->buckets = prime_list[i]; hash->limit = hash->buckets * max_hash_load; break; } } if(hash->buckets < size) { errno = ERANGE; free(hash); return NULL; } CALLOC(hash->hash_table, hash->buckets, sizeof(alpm_list_t *), \ free(hash); return NULL); return hash; } static unsigned int get_hash_position(unsigned long name_hash, alpm_pkghash_t *hash) { unsigned int position; position = name_hash % hash->buckets; /* collision resolution using open addressing with linear probing */ while(hash->hash_table[position] != NULL) { position += stride; while(position >= hash->buckets) { position -= hash->buckets; } } return position; } /* Expand the hash table size to the next increment and rebin the entries */ static alpm_pkghash_t *rehash(alpm_pkghash_t *oldhash) { alpm_pkghash_t *newhash; unsigned int newsize, i; /* Hash tables will need resized in two cases: * - adding packages to the local database * - poor estimation of the number of packages in sync database * * For small hash tables sizes (<500) the increase in size is by a * minimum of a factor of 2 for optimal rehash efficiency. For * larger database sizes, this increase is reduced to avoid excess * memory allocation as both scenarios requiring a rehash should not * require a table size increase that large. */ if(oldhash->buckets < 500) { newsize = oldhash->buckets * 2; } else if(oldhash->buckets < 2000) { newsize = oldhash->buckets * 3 / 2; } else if(oldhash->buckets < 5000) { newsize = oldhash->buckets * 4 / 3; } else { newsize = oldhash->buckets + 1; } newhash = _alpm_pkghash_create(newsize); if(newhash == NULL) { /* creation of newhash failed, stick with old one... */ return oldhash; } newhash->list = oldhash->list; oldhash->list = NULL; for(i = 0; i < oldhash->buckets; i++) { if(oldhash->hash_table[i] != NULL) { alpm_pkg_t *package = oldhash->hash_table[i]->data; unsigned int position = get_hash_position(package->name_hash, newhash); newhash->hash_table[position] = oldhash->hash_table[i]; oldhash->hash_table[i] = NULL; } } newhash->entries = oldhash->entries; _alpm_pkghash_free(oldhash); return newhash; } static alpm_pkghash_t *pkghash_add_pkg(alpm_pkghash_t *hash, alpm_pkg_t *pkg, int sorted) { alpm_list_t *ptr; unsigned int position; if(pkg == NULL || hash == NULL) { return hash; } if(hash->entries >= hash->limit) { hash = rehash(hash); } position = get_hash_position(pkg->name_hash, hash); ptr = malloc(sizeof(alpm_list_t)); if(ptr == NULL) { return hash; } ptr->data = pkg; ptr->prev = ptr; ptr->next = NULL; hash->hash_table[position] = ptr; if(!sorted) { hash->list = alpm_list_join(hash->list, ptr); } else { hash->list = alpm_list_mmerge(hash->list, ptr, _alpm_pkg_cmp); } hash->entries += 1; return hash; } alpm_pkghash_t *_alpm_pkghash_add(alpm_pkghash_t *hash, alpm_pkg_t *pkg) { return pkghash_add_pkg(hash, pkg, 0); } alpm_pkghash_t *_alpm_pkghash_add_sorted(alpm_pkghash_t *hash, alpm_pkg_t *pkg) { return pkghash_add_pkg(hash, pkg, 1); } static unsigned int move_one_entry(alpm_pkghash_t *hash, unsigned int start, unsigned int end) { /* Iterate backwards from 'end' to 'start', seeing if any of the items * would hash to 'start'. If we find one, we move it there and break. If * we get all the way back to position and find none that hash to it, we * also end iteration. Iterating backwards helps prevent needless shuffles; * we will never need to move more than one item per function call. The * return value is our current iteration location; if this is equal to * 'start' we can stop this madness. */ while(end != start) { alpm_list_t *i = hash->hash_table[end]; alpm_pkg_t *info = i->data; unsigned int new_position = get_hash_position(info->name_hash, hash); if(new_position == start) { hash->hash_table[start] = i; hash->hash_table[end] = NULL; break; } /* the odd math ensures we are always positive, e.g. * e.g. (0 - 1) % 47 == -1 * e.g. (47 + 0 - 1) % 47 == 46 */ end = (hash->buckets + end - stride) % hash->buckets; } return end; } /** * @brief Remove a package from a pkghash. * * @param hash the hash to remove the package from * @param pkg the package we are removing * @param data output parameter containing the removed item * * @return the resultant hash */ alpm_pkghash_t *_alpm_pkghash_remove(alpm_pkghash_t *hash, alpm_pkg_t *pkg, alpm_pkg_t **data) { alpm_list_t *i; unsigned int position; if(data) { *data = NULL; } if(pkg == NULL || hash == NULL) { return hash; } position = pkg->name_hash % hash->buckets; while((i = hash->hash_table[position]) != NULL) { alpm_pkg_t *info = i->data; if(info->name_hash == pkg->name_hash && strcmp(info->name, pkg->name) == 0) { unsigned int stop, prev; /* remove from list and hash */ hash->list = alpm_list_remove_item(hash->list, i); if(data) { *data = info; } hash->hash_table[position] = NULL; free(i); hash->entries -= 1; /* Potentially move entries following removed entry to keep open * addressing collision resolution working. We start by finding the * next null bucket to know how far we have to look. */ stop = position + stride; while(stop >= hash->buckets) { stop -= hash->buckets; } while(hash->hash_table[stop] != NULL && stop != position) { stop += stride; while(stop >= hash->buckets) { stop -= hash->buckets; } } stop = (hash->buckets + stop - stride) % hash->buckets; /* We now search backwards from stop to position. If we find an * item that now hashes to position, we will move it, and then try * to plug the new hole we just opened up, until we finally don't * move anything. */ while((prev = move_one_entry(hash, position, stop)) != position) { position = prev; } return hash; } position += stride; while(position >= hash->buckets) { position -= hash->buckets; } } return hash; } void _alpm_pkghash_free(alpm_pkghash_t *hash) { if(hash != NULL) { unsigned int i; for(i = 0; i < hash->buckets; i++) { free(hash->hash_table[i]); } free(hash->hash_table); } free(hash); } alpm_pkg_t *_alpm_pkghash_find(alpm_pkghash_t *hash, const char *name) { alpm_list_t *lp; unsigned long name_hash; unsigned int position; if(name == NULL || hash == NULL) { return NULL; } name_hash = _alpm_hash_sdbm(name); position = name_hash % hash->buckets; while((lp = hash->hash_table[position]) != NULL) { alpm_pkg_t *info = lp->data; if(info->name_hash == name_hash && strcmp(info->name, name) == 0) { return info; } position += stride; while(position >= hash->buckets) { position -= hash->buckets; } } return NULL; } /* vim: set ts=2 sw=2 noet: */