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97 lines
3.5 KiB
97 lines
3.5 KiB
// FlatWordPartitionScheme.java
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// ------------------------------
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// part of YaCy
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// (C) 2009 by Michael Peter Christen; mc@yacy.net
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// first published on http://yacy.net
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// Frankfurt, Germany, 28.01.2009
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//
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// $LastChangedDate: 2009-01-23 16:32:27 +0100 (Fr, 23 Jan 2009) $
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// $LastChangedRevision: 5514 $
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// $LastChangedBy: orbiter $
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//
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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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//
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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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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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package de.anomic.yacy.dht;
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import de.anomic.kelondro.order.Base64Order;
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import de.anomic.yacy.yacySeed;
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/**
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* A flat word partition scheme is a metric for words on the range of a distributed
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* hash table. The dht is reflected by a 0..Long.MAX_VALUE integer range, each word gets
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* a number on that range. To compute a number, the hash representation is used to compute
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* the hash position from the first 63 bits of the b64 hash string.
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*/
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public class FlatWordPartitionScheme implements PartitionScheme {
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public static final FlatWordPartitionScheme std = new FlatWordPartitionScheme();
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public FlatWordPartitionScheme() {
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// nothing to initialize
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}
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public int verticalPartitions() {
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return 1;
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}
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public long dhtPosition(byte[] wordHash, String urlHash) {
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// the urlHash has no relevance here
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// normalized to Long.MAX_VALUE
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return Base64Order.enhancedCoder.cardinal(wordHash);
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}
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public final long dhtDistance(final byte[] word, final String urlHash, final yacySeed peer) {
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return dhtDistance(word, urlHash, peer.hash.getBytes());
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}
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private final long dhtDistance(final byte[] from, final String urlHash, final byte[] to) {
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// the dht distance is a positive value between 0 and 1
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// if the distance is small, the word more probably belongs to the peer
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assert to != null;
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assert from != null;
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final long toPos = dhtPosition(to, null);
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final long fromPos = dhtPosition(from, urlHash);
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return dhtDistance(fromPos, toPos);
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}
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public long dhtPosition(byte[] wordHash, int verticalPosition) {
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return dhtPosition(wordHash, null);
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}
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public long[] dhtPositions(byte[] wordHash) {
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long[] l = new long[1];
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l[1] = dhtPosition(wordHash, null);
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return l;
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}
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public int verticalPosition(String urlHash) {
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return 0; // this is not a method stub, this is actually true for all FlatWordPartitionScheme
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}
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public final static long dhtDistance(final long fromPos, final long toPos) {
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return (toPos >= fromPos) ?
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toPos - fromPos :
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(Long.MAX_VALUE - fromPos) + toPos + 1;
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}
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public static byte[] positionToHash(final long l) {
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// transform the position of a peer position into a close peer hash
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String s = new String(Base64Order.enhancedCoder.uncardinal(l));
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while (s.length() < 12) s += "A";
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return s.getBytes();
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}
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}
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