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Core sketch algorithms used alone and by other Java repositories in the DataSketches library.
There is a newer version: 7.0.0
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.datasketches.theta;

import static org.apache.datasketches.Util.checkSeedHashes;
import static org.apache.datasketches.Util.computeSeedHash;
import static org.apache.datasketches.theta.PreambleUtil.COMPACT_FLAG_MASK;
import static org.apache.datasketches.theta.PreambleUtil.EMPTY_FLAG_MASK;
import static org.apache.datasketches.theta.PreambleUtil.READ_ONLY_FLAG_MASK;
import static org.apache.datasketches.theta.PreambleUtil.SEED_HASH_SHORT;

import org.apache.datasketches.memory.Memory;
import org.apache.datasketches.memory.WritableMemory;

/**
 * An off-heap (Direct), compact, unordered, read-only sketch.  This sketch can only be associated
 * with a Serialization Version 3 format binary image.
 *
 * This implementation uses data in a given Memory that is owned and managed by the caller.
 * This Memory can be off-heap, which if managed properly will greatly reduce the need for
 * the JVM to perform garbage collection.
 *
 * @author Lee Rhodes
 */
final class DirectCompactUnorderedSketch extends DirectCompactSketch {

  DirectCompactUnorderedSketch(final Memory mem) {
    super(mem);
  }

  /**
   * Wraps the given Memory, which must be a SerVer 3, unordered, Compact Sketch image.
   * Must check the validity of the Memory before calling.
   * @param srcMem See Memory
   * @param seed See Update Hash Seed.
   * @return this sketch
   */
  static DirectCompactUnorderedSketch wrapInstance(final Memory srcMem, final long seed) {
    final short memSeedHash = srcMem.getShort(SEED_HASH_SHORT);
    final short computedSeedHash = computeSeedHash(seed);
    checkSeedHashes(memSeedHash, computedSeedHash);
    return new DirectCompactUnorderedSketch(srcMem);
  }

  /**
   * Constructs this sketch from correct, valid components.
   * @param cache in compact, ordered form
   * @param empty The correct Empty.
   * @param seedHash The correct
   * Seed Hash.
   * @param curCount correct value
   * @param thetaLong The correct
   * thetaLong.
   * @param dstMem the given destination Memory. This clears it before use.
   * @return a DirectCompactUnorderedSketch
   */
  static DirectCompactUnorderedSketch compact(final long[] cache, final boolean empty,
      final short seedHash, final int curCount, final long thetaLong, final WritableMemory dstMem) {
    final int preLongs = computeCompactPreLongs(thetaLong, empty, curCount);
    final int requiredFlags = READ_ONLY_FLAG_MASK | COMPACT_FLAG_MASK;
    final byte flags = (byte) (requiredFlags | (empty ? EMPTY_FLAG_MASK : 0));
    loadCompactMemory(cache, seedHash, curCount, thetaLong, dstMem, flags, preLongs);
    return new DirectCompactUnorderedSketch(dstMem);
  }

  @Override
  public boolean isOrdered() {
    return false;
  }

}