path: root/base/util/src/netscape/security/util/BitArray.java

// --- BEGIN COPYRIGHT BLOCK ---
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; version 2 of the License.
//
// 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 for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program; if not, write to the Free Software Foundation, Inc.,
// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
//
// (C) 2007 Red Hat, Inc.
// All rights reserved.
// --- END COPYRIGHT BLOCK ---
package netscape.security.util;

import java.io.ByteArrayOutputStream;

/**
 * A packed array of booleans.
 * 
 * @author Joshua Bloch
 * @author Douglas Hoover
 * @version 1.2 97/12/10
 */

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 (repn.length > 0)
            repn[repn.length - 1] = (byte) (repn[repn.length - 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());

    }

}