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;
    }
    

    public int lengthInBits(String key) {
        return key.length() * size;
    }

    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;
    }
    

    public boolean isPrefix(String key, String prefix) {
        return key.startsWith(prefix);
    }
    

    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;
    }
}