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package de.lmu.ifi.dbs.elki.utilities;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2014
Ludwig-Maximilians-Universität München
Lehr- und Forschungseinheit für Datenbanksysteme
ELKI Development Team
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 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 Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.BitSet;
import java.util.Comparator;
import java.util.Random;
/**
* This class collects various static helper methods.
*
* For helper methods related to special application fields see other utilities
* classes.
*
* @see de.lmu.ifi.dbs.elki.utilities
*/
public final class Util {
/**
* Prime number used in hash code computation.
*/
private static final long HASHPRIME = 2654435761L;
/**
* Detect Java 7.
*/
public static final boolean IS_JAVA7 = System.getProperty("java.version").startsWith("1.7.");
/**
* Detect Oracle Java.
*/
public static final boolean IS_ORACLE_JAVA = System.getProperty("java.vm.vendor").startsWith("Oracle");
/**
* Fake constructor: do not instantiate.
*/
private Util() {
// Do not instantiate.
}
/**
* Creates a new BitSet of fixed cardinality with randomly set bits.
*
* @param cardinality the cardinality of the BitSet to create
* @param capacity the capacity of the BitSet to create - the randomly
* generated indices of the bits set to true will be uniformly
* distributed between 0 (inclusive) and capacity (exclusive)
* @param random a Random Object to create the sequence of indices set to true
* - the same number occurring twice or more is ignored but the already
* selected bit remains true
* @return a new BitSet with randomly set bits
*/
public static BitSet randomBitSet(int cardinality, int capacity, Random random) {
assert (cardinality >= 0) : "Cannot set a negative number of bits!";
assert (cardinality < capacity) : "Cannot set " + cardinality + " of " + capacity + " bits!";
BitSet bitset = new BitSet(capacity);
if(cardinality < capacity >>> 1) {
while(bitset.cardinality() < cardinality) {
bitset.set(random.nextInt(capacity));
}
}
else {
bitset.flip(0, capacity);
while(bitset.cardinality() > cardinality) {
bitset.clear(random.nextInt(capacity));
}
}
return bitset;
}
/**
* Mix multiple hashcodes into one.
*
* @param hash Single Hashcodes to "mix"
* @return Original hash code
*/
@Deprecated
public static int mixHashCodes(int hash) {
return hash;
}
/**
* Mix multiple hashcodes into one.
*
* @param hash1 First hashcode to mix
* @param hash2 Second hashcode to mix
* @return Mixed hash code
*/
public static int mixHashCodes(int hash1, int hash2) {
return (int) (hash1 * HASHPRIME + hash2);
}
/**
* Mix multiple hashcodes into one.
*
* @param hash1 First hashcode to mix
* @param hash2 Second hashcode to mix
* @param hash3 Third hashcode to mix
* @return Mixed hash code
*/
public static int mixHashCodes(int hash1, int hash2, int hash3) {
long result = hash1 * HASHPRIME + hash2;
return (int) (result * HASHPRIME + hash3);
}
/**
* Mix multiple hashcodes into one.
*
* @param hash Hashcodes to mix
* @return Mixed hash code
*/
public static int mixHashCodes(int... hash) {
if(hash.length == 0) {
return 0;
}
long result = hash[0];
for(int i = 1; i < hash.length; i++) {
result = result * HASHPRIME + hash[i];
}
return (int) result;
}
/**
* Static instance.
*/
private static final Comparator<?> FORWARD = new ForwardComparator();
/**
* Regular comparator. See {@link java.util.Collections#reverseOrder()} for a
* reverse comparator.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
private static final class ForwardComparator implements Comparator<Comparable<Object>> {
@Override
public int compare(Comparable<Object> o1, Comparable<Object> o2) {
return o1.compareTo(o2);
}
}
/**
* Compare two objects, forward. See
* {@link java.util.Collections#reverseOrder()} for a reverse comparator.
*
* @param <T> Object type
* @return Forward comparator
*/
@SuppressWarnings("unchecked")
public static <T> Comparator<T> forwardOrder() {
return (Comparator<T>) FORWARD;
}
}
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