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Common functionality for HBase
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/*
 * 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.hadoop.hbase.util;

import org.apache.yetus.audience.InterfaceAudience;

/**
 * Used to describe or modify the lexicographical sort order of a {@code byte[]}. Default ordering
 * is considered {@code ASCENDING}. The order of a {@code byte[]} can be inverted, resulting in
 * {@code DESCENDING} order, by replacing each byte with its 1's compliment.
 */
@InterfaceAudience.Public
public enum Order {
  ASCENDING {
    @Override
    public int cmp(int cmp) {
      /* noop */ return cmp;
    }

    @Override
    public byte apply(byte val) {
      /* noop */ return val;
    }

    @Override
    public void apply(byte[] val) {
      /* noop */
    }

    @Override
    public void apply(byte[] val, int offset, int length) {
      /* noop */
    }

    @Override
    public String toString() {
      return "ASCENDING";
    }
  },

  DESCENDING {
    /**
     * A {@code byte} value is inverted by taking its 1's Complement, achieved via {@code xor} with
     * {@code 0xff}.
     */
    private static final byte MASK = (byte) 0xff;

    @Override
    public int cmp(int cmp) {
      return -1 * cmp;
    }

    @Override
    public byte apply(byte val) {
      return (byte) (val ^ MASK);
    }

    @Override
    public void apply(byte[] val) {
      for (int i = 0; i < val.length; i++) {
        val[i] ^= MASK;
      }
    }

    @Override
    public void apply(byte[] val, int offset, int length) {
      for (int i = 0; i < length; i++) {
        val[offset + i] ^= MASK;
      }
    }

    @Override
    public String toString() {
      return "DESCENDING";
    }
  };

  /**
   * Returns the adjusted trichotomous value according to the ordering imposed by this
   * {@code Order}.
   */
  public abstract int cmp(int cmp);

  /**
   * Apply order to the byte {@code val}.
   */
  public abstract byte apply(byte val);

  /**
   * Apply order to the byte array {@code val}.
   */
  public abstract void apply(byte[] val);

  /**
   * Apply order to a range within the byte array {@code val}.
   */
  public abstract void apply(byte[] val, int offset, int length);
}