/* * pkghash.c * * Copyright (c) 2011 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. */ static const size_t prime_list[] = { 11ul, 13ul, 17ul, 19ul, 23ul, 29ul, 31ul, 37ul, 41ul, 43ul, 47ul, 53ul, 59ul, 61ul, 67ul, 71ul, 73ul, 79ul, 83ul, 89ul, 97ul, 103ul, 109ul, 113ul, 127ul, 137ul, 139ul, 149ul, 157ul, 167ul, 179ul, 193ul, 199ul, 211ul, 227ul, 241ul, 257ul, 277ul, 293ul, 313ul, 337ul, 359ul, 383ul, 409ul, 439ul, 467ul, 503ul, 541ul, 577ul, 619ul, 661ul, 709ul, 761ul, 823ul, 887ul, 953ul, 1031ul, 1109ul, 1193ul, 1289ul, 1381ul, 1493ul, 1613ul, 1741ul, 1879ul, 2029ul, 2179ul, 2357ul, 2549ul, 2753ul, 2971ul, 3209ul, 3469ul, 3739ul, 4027ul, 4349ul, 4703ul, 5087ul, 5503ul, 5953ul, 6427ul, 6949ul, 7517ul, 8123ul, 8783ul, 9497ul, 10273ul, 11113ul, 12011ul, 12983ul, 14033ul, 15173ul, 16411ul, 17749ul, 19183ul, 20753ul, 22447ul, 24281ul, 26267ul, 28411ul, 30727ul, 33223ul, 35933ul, 38873ul, 42043ul, 45481ul, 49201ul, 53201ul, 57557ul, 62233ul, 67307ul, 72817ul, 78779ul, 85229ul, 92203ul, 99733ul, 107897ul, 116731ul, 126271ul, 136607ul, 147793ul, 159871ul, 172933ul, 187091ul, 202409ul, 218971ul, 236897ul, 256279ul, 277261ul, 299951ul, 324503ul, 351061ul, 379787ul, 410857ul, 444487ul, 480881ul, 520241ul, 562841ul, 608903ul, 658753ul, 712697ul, 771049ul, 834181ul, 902483ul, 976369ul }; /* Allocate a hash table with at least "size" buckets */ alpm_pkghash_t *_alpm_pkghash_create(size_t size) { alpm_pkghash_t *hash = NULL; size_t i, loopsize; CALLOC(hash, 1, sizeof(alpm_pkghash_t), return NULL); loopsize = sizeof(prime_list) / sizeof(*prime_list); for(i = 0; i < loopsize; i++) { if(prime_list[i] > size) { hash->buckets = prime_list[i]; 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 size_t get_hash_position(unsigned long name_hash, alpm_pkghash_t *hash) { size_t position; position = name_hash % hash->buckets; /* collision resolution using open addressing with linear probing */ while(hash->hash_table[position] != NULL) { position = (position + 1) % 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; size_t newsize, position, 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; 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; size_t position; if(pkg == NULL || hash == NULL) { return hash; } if((hash->entries + 1) / MAX_HASH_LOAD > hash->buckets) { hash = rehash(hash); } position = get_hash_position(pkg->name_hash, hash); ptr = calloc(1, sizeof(alpm_list_t)); if(ptr == NULL) { return hash; } ptr->data = pkg; ptr->next = NULL; ptr->prev = ptr; 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 size_t move_one_entry(alpm_pkghash_t *hash, size_t start, size_t 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; size_t 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 - 1) % 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; size_t 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) { size_t 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 + 1) % hash->buckets; while(hash->hash_table[stop] != NULL && stop != position) { stop = (stop + 1) % hash->buckets; } stop = (hash->buckets + stop - 1) % 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 = (position + 1) % hash->buckets; } return hash; } void _alpm_pkghash_free(alpm_pkghash_t *hash) { size_t i; if(hash != NULL) { 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; size_t 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 = (position + 1) % hash->buckets; } return NULL; } /* vim: set ts=2 sw=2 noet: */