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Apache Geode provides a database-like consistency model, reliable transaction processing and a shared-nothing architecture to maintain very low latency performance with high concurrency processing

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/*
 * Copyright (C) 2012 Clearspring Technologies, Inc.
 *
 * Licensed 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.geode.internal.hll;


public class RegisterSet {

  public final static int LOG2_BITS_PER_WORD = 6;
  public final static int REGISTER_SIZE = 5;

  public final int count;
  public final int size;

  private final int[] M;

  public RegisterSet(int count) {
    this(count, null);
  }

  public RegisterSet(int count, int[] initialValues) {
    this.count = count;

    if (initialValues == null) {
      this.M = new int[getSizeForCount(count)];
    } else {
      this.M = initialValues;
    }
    this.size = this.M.length;
  }

  public static int getBits(int count) {
    return count / LOG2_BITS_PER_WORD;
  }

  public static int getSizeForCount(int count) {
    int bits = getBits(count);
    if (bits == 0) {
      return 1;
    } else if (bits % Integer.SIZE == 0) {
      return bits;
    } else {
      return bits + 1;
    }
  }

  public void set(int position, int value) {
    int bucketPos = position / LOG2_BITS_PER_WORD;
    int shift = REGISTER_SIZE * (position - (bucketPos * LOG2_BITS_PER_WORD));
    this.M[bucketPos] = (this.M[bucketPos] & ~(0x1f << shift)) | (value << shift);
  }

  public int get(int position) {
    int bucketPos = position / LOG2_BITS_PER_WORD;
    int shift = REGISTER_SIZE * (position - (bucketPos * LOG2_BITS_PER_WORD));
    return (this.M[bucketPos] & (0x1f << shift)) >>> shift;
  }

  public boolean updateIfGreater(int position, int value) {
    int bucket = position / LOG2_BITS_PER_WORD;
    int shift = REGISTER_SIZE * (position - (bucket * LOG2_BITS_PER_WORD));
    int mask = 0x1f << shift;

    // Use long to avoid sign issues with the left-most shift
    long curVal = this.M[bucket] & mask;
    long newVal = value << shift;
    if (curVal < newVal) {
      this.M[bucket] = (int) ((this.M[bucket] & ~mask) | newVal);
      return true;
    } else {
      return false;
    }
  }

  public void merge(RegisterSet that) {
    for (int bucket = 0; bucket < M.length; bucket++) {
      int word = 0;
      for (int j = 0; j < LOG2_BITS_PER_WORD; j++) {
        int mask = 0x1f << (REGISTER_SIZE * j);

        int thisVal = (this.M[bucket] & mask);
        int thatVal = (that.M[bucket] & mask);
        word |= (thisVal < thatVal) ? thatVal : thisVal;
      }
      this.M[bucket] = word;
    }
  }

  int[] readOnlyBits() {
    return M;
  }

  public int[] bits() {
    int[] copy = new int[size];
    System.arraycopy(M, 0, copy, 0, M.length);
    return copy;
  }
}