pacman/lib/libalpm/pkghash.c

/*
 *  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 = 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 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: */