bitarray.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 270 行

/*
 * @(#)BitArray.java	1.14 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package sun.security.util;

import java.io.ByteArrayOutputStream;

/**
 * A packed array of booleans.
 *
 * @author Joshua Bloch
 * @author Douglas Hoover
 * @version 1.7 02/02/00
 */

public class BitArray {

    private byte[] repn;
    private int length;

    private static final int BITS_PER_UNIT = 8;

    private static int subscript(int idx) {
	return idx / BITS_PER_UNIT;
    }

    private static int position(int idx) { // bits big-endian in each unit
	return 1 << (BITS_PER_UNIT - 1 - (idx % BITS_PER_UNIT));
    }

    /**
     * Creates a BitArray of the specified size, initialized to zeros.
     */
    public BitArray(int length) throws IllegalArgumentException {
	if (length < 0) {
	    throw new IllegalArgumentException("Negative length for BitArray");
	}

	this.length = length;

	repn = new byte[(length + BITS_PER_UNIT - 1)/BITS_PER_UNIT]; 
    }


    /**
     * Creates a BitArray of the specified size, initialized from the
     * specified byte array.  The most significant bit of a[0] gets
     * index zero in the BitArray.  The array a must be large enough
     * to specify a value for every bit in the BitArray.  In other words,
     * 8*a.length <= length.
     */
    public BitArray(int length, byte[] a) throws IllegalArgumentException {
	
	if (length < 0) {
	    throw new IllegalArgumentException("Negative length for BitArray");
	}
	if (a.length * BITS_PER_UNIT < length) {
	    throw new IllegalArgumentException("Byte array too short to represent " +
					       "bit array of given length");
	}

	this.length = length;

	int repLength = ((length + BITS_PER_UNIT - 1)/BITS_PER_UNIT);
	int unusedBits = repLength*BITS_PER_UNIT - length;
	byte bitMask = (byte) (0xFF << unusedBits); 

	/* 
	 normalize the representation:
	  1. discard extra bytes
	  2. zero out extra bits in the last byte
	 */
	repn = new byte[repLength]; 
	System.arraycopy(a, 0, repn, 0, repLength);
	if (repLength > 0) {
	    repn[repLength - 1] &= bitMask;
	}
    }

    /**
     * Create a BitArray whose bits are those of the given array 
     * of Booleans. 
     */
    public BitArray(boolean[] bits) {
	length = bits.length;
	repn = new byte[(length + 7)/8];

	for (int i=0; i < length; i++) {
	    set(i, bits[i]);
	}
    }
	
	
    /**
     *  Copy constructor (for cloning).
     */
    private BitArray(BitArray ba) {
	length = ba.length;
	repn = (byte[]) ba.repn.clone();
    }

    /**
     *  Returns the indexed bit in this BitArray.
     */
    public boolean get(int index) throws ArrayIndexOutOfBoundsException {
	if (index < 0 || index >= length) {
	    throw new ArrayIndexOutOfBoundsException(Integer.toString(index));
	}
	
	return (repn[subscript(index)] & position(index)) != 0;
    }

    /**
     *  Sets the indexed bit in this BitArray.
     */
    public void set(int index, boolean value)
    throws ArrayIndexOutOfBoundsException {
	if (index < 0 || index >= length) {
	    throw new ArrayIndexOutOfBoundsException(Integer.toString(index));
	}
	int idx = subscript(index);
	int bit = position(index);

	if (value) {
	    repn[idx] |= bit;
	} else {
	    repn[idx] &= ~bit;
	}
    }

    /**
     * Returns the length of this BitArray.
     */
    public int length() {
	return length;
    }

    /**
     * Returns a Byte array containing the contents of this BitArray.
     * The bit stored at index zero in this BitArray will be copied
     * into the most significant bit of the zeroth element of the 
     * returned byte array.  The last byte of the returned byte array
     * will be contain zeros in any bits that do not have corresponding
     * bits in the BitArray.  (This matters only if the BitArray's size
     * is not a multiple of 8.)
     */ 
    public byte[] toByteArray() {
	return (byte[]) repn.clone();
    }

    public boolean equals(Object obj) {
	if (obj == this) return true;
	if (obj == null || !(obj instanceof BitArray)) return false;

	BitArray ba = (BitArray) obj;
	
	if (ba.length != length) return false;
	
	for (int i = 0; i < repn.length; i += 1) {
	    if (repn[i] != ba.repn[i]) return false;
	}
	return true;
    }

    /**
     * Return a boolean array with the same bit values a this BitArray.
     */
    public boolean[] toBooleanArray() {
	boolean[] bits = new boolean[length];

	for (int i=0; i < length; i++) {
	    bits[i] = get(i);
	}
	return bits;
    }

    /**
     * Returns a hash code value for this bit array.
     *
     * @return  a hash code value for this bit array.
     */
    public int hashCode() {
	int hashCode = 0;

	for (int i = 0; i < repn.length; i++)
	    hashCode = 31*hashCode + repn[i];

	return hashCode ^ length;
    }


    public Object clone() {
	return new BitArray(this);
    }


    private static final byte[][] NYBBLE = {
	{ (byte)'0',(byte)'0',(byte)'0',(byte)'0'}, 
	{ (byte)'0',(byte)'0',(byte)'0',(byte)'1'}, 
	{ (byte)'0',(byte)'0',(byte)'1',(byte)'0'}, 
	{ (byte)'0',(byte)'0',(byte)'1',(byte)'1'}, 
	{ (byte)'0',(byte)'1',(byte)'0',(byte)'0'}, 
	{ (byte)'0',(byte)'1',(byte)'0',(byte)'1'}, 
	{ (byte)'0',(byte)'1',(byte)'1',(byte)'0'}, 
	{ (byte)'0',(byte)'1',(byte)'1',(byte)'1'}, 
	{ (byte)'1',(byte)'0',(byte)'0',(byte)'0'}, 
	{ (byte)'1',(byte)'0',(byte)'0',(byte)'1'}, 
	{ (byte)'1',(byte)'0',(byte)'1',(byte)'0'}, 
	{ (byte)'1',(byte)'0',(byte)'1',(byte)'1'}, 
	{ (byte)'1',(byte)'1',(byte)'0',(byte)'0'}, 
	{ (byte)'1',(byte)'1',(byte)'0',(byte)'1'}, 
	{ (byte)'1',(byte)'1',(byte)'1',(byte)'0'}, 
	{ (byte)'1',(byte)'1',(byte)'1',(byte)'1'}
    };

    private static final int BYTES_PER_LINE = 8;

    /**
     *  Returns a string representation of this BitArray.
     */
    public String toString() {
	ByteArrayOutputStream out = new ByteArrayOutputStream();
	
	for (int i = 0; i < repn.length - 1; i++) {
	    out.write(NYBBLE[(repn[i] >> 4) & 0x0F], 0, 4);
	    out.write(NYBBLE[repn[i] & 0x0F], 0, 4);
	   
	    if (i % BYTES_PER_LINE == BYTES_PER_LINE - 1) {
		out.write('\n');
	    } else {
		out.write(' ');
	    }
	}

	// in last byte of repn, use only the valid bits
	for (int i = BITS_PER_UNIT * (repn.length - 1); i < length; i++) {
	    out.write(get(i) ? '1' : '0');
	}

	return new String(out.toByteArray());
	
    }
		     
}