ByteKeyAnalyzer.java

/*
 * Copyright 2005-2010 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 Byte}s
 */
public class ByteKeyAnalyzer extends AbstractKeyAnalyzer<Byte> implements Serializable {
    
    private static final long serialVersionUID = -5294514513354687850L;

    /**
     * A singleton instance of {@link ByteKeyAnalyzer}
     */
    public static final ByteKeyAnalyzer INSTANCE = new ByteKeyAnalyzer();
    
    /**
     * A bit mask where the first bit is 1 and the others are zero
     */
    private static final int MSB = 1 << Byte.SIZE-1;
    
    /**
     * Returns a bit mask where the given bit is set
     */
    private static int mask(int bit) {
        return MSB >>> bit;
    }
    

    public int lengthInBits(Byte key) {
        return Byte.SIZE;
    }


    public boolean isBitSet(Byte key, int bitIndex) {
        return (key & mask(bitIndex)) != 0;
    }


    public int bitIndex(Byte key, Byte otherKey) {
        byte keyValue = key.byteValue();
        if (keyValue == 0) {
            return NULL_BIT_KEY;
        }

        byte otherValue = otherKey.byteValue();
        
        if (keyValue != otherValue) {
            int xorValue = keyValue ^ otherValue;
            for (int i = 0; i < Byte.SIZE; i++) {
                if ((xorValue & mask(i)) != 0) {
                    return i;
                }
            }
        }
        
        return KeyAnalyzer.EQUAL_BIT_KEY;
    }


    public boolean isPrefix(Byte key, Byte prefix) {
        return key.equals(prefix);
    }
}