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1   /*
2    * Copyright 2020 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License, version 2.0 (the
5    * "License"); you may not use this file except in compliance with the License. You may obtain a
6    * copy of the License at:
7    *
8    * https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software distributed under the License
11   * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
12   * or implied. See the License for the specific language governing permissions and limitations under
13   * the License.
14   */
15  package io.netty.buffer.search;
16  
17  import io.netty.util.internal.PlatformDependent;
18  
19  /**
20   * Implements <a href="https://en.wikipedia.org/wiki/Bitap_algorithm">Bitap</a> string search algorithm.
21   * Use static {@link AbstractSearchProcessorFactory#newBitapSearchProcessorFactory}
22   * to create an instance of this factory.
23   * Use {@link BitapSearchProcessorFactory#newSearchProcessor} to get an instance of {@link io.netty.util.ByteProcessor}
24   * implementation for performing the actual search.
25   * @see AbstractSearchProcessorFactory
26   */
27  public class BitapSearchProcessorFactory extends AbstractSearchProcessorFactory {
28  
29      private final long[] bitMasks = new long[256];
30      private final long successBit;
31  
32      public static class Processor implements SearchProcessor {
33  
34          private final long[] bitMasks;
35          private final long successBit;
36          private long currentMask;
37  
38          Processor(long[] bitMasks, long successBit) {
39              this.bitMasks = bitMasks;
40              this.successBit = successBit;
41          }
42  
43          @Override
44          public boolean process(byte value) {
45              currentMask = ((currentMask << 1) | 1) & PlatformDependent.getLong(bitMasks, value & 0xffL);
46              return (currentMask & successBit) == 0;
47          }
48  
49          @Override
50          public void reset() {
51              currentMask = 0;
52          }
53      }
54  
55      BitapSearchProcessorFactory(byte[] needle) {
56          if (needle.length > 64) {
57              throw new IllegalArgumentException("Maximum supported search pattern length is 64, got " + needle.length);
58          }
59  
60          long bit = 1L;
61          for (byte c: needle) {
62              bitMasks[c & 0xff] |= bit;
63              bit <<= 1;
64          }
65  
66          successBit = 1L << (needle.length - 1);
67      }
68  
69      /**
70       * Returns a new {@link Processor}.
71       */
72      @Override
73      public Processor newSearchProcessor() {
74          return new Processor(bitMasks, successBit);
75      }
76  
77  }