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1   /*
2    * Copyright 2010 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  
21  package org.apache.hadoop.hbase.filter;
22  
23  import java.io.DataInput;
24  import java.io.DataOutput;
25  import java.io.IOException;
26  
27  /**
28   * A bit comparator which performs the specified bitwise operation on each of the bytes
29   * with the specified byte array. Then returns whether the result is non-zero.
30   */
31  public class BitComparator extends WritableByteArrayComparable {
32  
33    /** Nullary constructor for Writable, do not use */
34    public BitComparator() {}
35  
36    /** Bit operators. */
37    public enum BitwiseOp {
38      /** and */
39      AND,
40      /** or */
41      OR,
42      /** xor */
43      XOR
44    }
45    protected BitwiseOp bitOperator;
46  
47    /**
48     * Constructor
49     * @param value value
50     * @param bitOperator operator to use on the bit comparison
51     */
52    public BitComparator(byte[] value, BitwiseOp bitOperator) {
53      super(value);
54      this.bitOperator = bitOperator;
55    }
56  
57    /**
58     * @return the bitwise operator
59     */
60    public BitwiseOp getOperator() {
61      return bitOperator;
62    }
63  
64    @Override
65    public void readFields(DataInput in) throws IOException {
66      super.readFields(in);
67      bitOperator = BitwiseOp.valueOf(in.readUTF());
68    }
69  
70    @Override
71    public void write(DataOutput out) throws IOException {
72      super.write(out);
73      out.writeUTF(bitOperator.name());
74    }
75  
76    @Override
77    public int compareTo(byte[] value, int offset, int length) {
78      if (length != this.value.length) {
79        return 1;
80      }
81      int b = 0;
82      //Iterating backwards is faster because we can quit after one non-zero byte.
83      for (int i = length - 1; i >= 0 && b == 0; i--) {
84        switch (bitOperator) {
85          case AND:
86            b = (this.value[i] & value[i+offset]) & 0xff;
87            break;
88          case OR:
89            b = (this.value[i] | value[i+offset]) & 0xff;
90            break;
91          case XOR:
92            b = (this.value[i] ^ value[i+offset]) & 0xff;
93            break;
94        }
95      }
96      return b == 0 ? 1 : 0;
97    }
98  }
99