StringKeyAnalyzer.java

/*
 * Copyright 2010 Roger Kapsi
 *
 *   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.ardverk.collection;

import java.io.Serializable;

/**
 * A {@link KeyAnalyzer} for {@link String}s.
 */
public class StringKeyAnalyzer extends AbstractKeyAnalyzer<String> 
    implements Serializable {
  
  private static final long serialVersionUID = 7677641007465182788L;

  /**
   * A {@link StringKeyAnalyzer} that uses all bits (16) of a {@code char}.
   */
  public static final StringKeyAnalyzer CHAR = new StringKeyAnalyzer(Character.SIZE);

  /**
   * A {@link StringKeyAnalyzer} that uses only the lower 8 bits of each {@code char}.
   */
  public static final StringKeyAnalyzer BYTE = new StringKeyAnalyzer(Byte.SIZE);
  
  @Deprecated
  public static final StringKeyAnalyzer INSTANCE = CHAR;
  
  private final int size;
  
  private final int msb;
  
  private StringKeyAnalyzer(int size) {
    this(size, 1 << size-1);
  }
  
  private StringKeyAnalyzer(int size, int msb) {
    this.size = size;
    this.msb = msb;
  }
  
  /**
   * Returns a bit mask where the given bit is set
   */
  private int mask(int bit) {
    return msb >>> bit;
  }
  
  /**
   * Returns the {@code char} at the given index.
   */
  private char valueAt(String value, int index) {
    if (index < value.length()) {
      char ch = value.charAt(index);
      if (size == Byte.SIZE) {
        ch &= 0xFF;
      }
      return ch;
    }
    return 0;
  }
  
  @Override
  public int lengthInBits(String key) {
    return key.length() * size;
  }

  @Override
  public boolean isBitSet(String key, int bitIndex) {
    if (bitIndex >= lengthInBits(key)) {
      return false;
    }
    
    int index = (int)(bitIndex / size);
    int bit = (int)(bitIndex % size);
    
    return (key.charAt(index) & mask(bit)) != 0;
  }
  
  @Override
  public boolean isPrefix(String key, String prefix) {
    return key.startsWith(prefix);
  }
  
  @Override
  public int bitIndex(String key, String otherKey) {
    
    boolean allNull = true;
    int length = Math.max(key.length(), otherKey.length());
    
    for (int i = 0; i < length; i++) {
      
      char ch1 = valueAt(key, i);
      char ch2 = valueAt(otherKey, i);
      
      if (ch1 != ch2) {
        int xor = ch1 ^ ch2;
        for (int j = 0; j < size; j++) {
          if ((xor & mask(j)) != 0) {
            return (i * size) + j;
          }
        }
      }
      
      if (ch1 != 0) {
        allNull = false;
      }
    }
    
    // All bits are 0
    if (allNull) {
      return KeyAnalyzer.NULL_BIT_KEY;
    }
    
    // Both keys are equal
    return KeyAnalyzer.EQUAL_BIT_KEY;
  }
}