/*
 * @(#)BitSet.java	1.46 00/02/02
 *
 * Copyright 1995-2000 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

package java.util;

import java.io.*;

/**
 * This class implements a vector of bits that grows as needed. Each 
 * component of the bit set has a <code>boolean</code> value. The 
 * bits of a <code>BitSet</code> are indexed by nonnegative integers. 
 * Individual indexed bits can be examined, set, or cleared. One 
 * <code>BitSet</code> may be used to modify the contents of another 
 * <code>BitSet</code> through logical AND, logical inclusive OR, and 
 * logical exclusive OR operations.
 * <p>
 * By default, all bits in the set initially have the value 
 * <code>false</code>. 
 * <p>
 * Every bit set has a current size, which is the number of bits 
 * of space currently in use by the bit set. Note that the size is
 * related to the implementation of a bit set, so it may change with
 * implementation. The length of a bit set relates to logical length
 * of a bit set and is defined independently of implementation.
 *
 * @author  Arthur van Hoff
 * @author  Michael McCloskey
 * @version 1.46, 02/02/00
 * @since   JDK1.0
 */
public class BitSet implements Cloneable, java.io.Serializable {
    /*
     * BitSets are packed into arrays of "units."  Currently a unit is a long,
     * which consists of 64 bits, requiring 6 address bits.  The choice of unit
     * is determined purely by performance concerns.
     */
    private final static int ADDRESS_BITS_PER_UNIT = 6;
    private final static int BITS_PER_UNIT = 1 << ADDRESS_BITS_PER_UNIT;
    private final static int BIT_INDEX_MASK = BITS_PER_UNIT - 1;

    /**
     * The bits in this BitSet.  The ith bit is stored in bits[i/64] at
     * bit position i % 64 (where bit position 0 refers to the least
     * significant bit and 63 refers to the most significant bit).
     * INVARIANT: The words in bits[] above unitInUse-1 are zero.
     *
     * @serial
     */
    private long bits[];  // this should be called unit[]

    /**
     * The number of units in the logical size of this BitSet.
     * INVARIANT: unitsInUse is nonnegative.
     * INVARIANT: bits[unitsInUse-1] is nonzero unless unitsInUse is zero.
     */
    private transient int unitsInUse = 0;

    /* use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 7997698588986878753L;

    /**
     * Given a bit index return unit index containing it.
     */
    private static int unitIndex(int bitIndex) {
        return bitIndex >> ADDRESS_BITS_PER_UNIT;
    }

    /**
     * Given a bit index, return a unit that masks that bit in its unit.
     */
    private static long bit(int bitIndex) {
        return 1L << (bitIndex & BIT_INDEX_MASK);
    }

    /**
     * Set the field unitsInUse with the logical size in units of the bit
     * set.  WARNING:This function assumes that the number of units actually
     * in use is less than or equal to the current value of unitsInUse!
     */
    private void recalculateUnitsInUse() {
        /* Traverse the bitset until a used unit is found */
        int i;
        for (i = unitsInUse-1; i >= 0; i--)
	    if(bits[i] != 0)
		break; //this unit is in use!

        unitsInUse = i+1; //the new logical size
    }

    /**
     * Creates a new bit set. All bits are initially <code>false</code>.
     */
    public BitSet() {
	this(BITS_PER_UNIT);
    }

    /**
     * Creates a bit set whose initial size is large enough to explicitly
     * represent bits with indices in the range <code>0</code> through
     * <code>nbits-1</code>. All bits are initially <code>false</code>. 
     *
     * @param     nbits   the initial size of the bit set.
     * @exception NegativeArraySizeException if the specified initial size
     *               is negative.
     */
    public BitSet(int nbits) {
	/* nbits can't be negative; size 0 is OK */
	if (nbits < 0)
	    throw new NegativeArraySizeException(Integer.toString(nbits));

	bits = new long[(unitIndex(nbits-1) + 1)];
    }

    /**
     * Ensures that the BitSet can hold enough units.
     * @param	unitsRequired the minimum acceptable number of units.
     */
    private void ensureCapacity(int unitsRequired) {
	if (bits.length < unitsRequired) {
	    /* Allocate larger of doubled size or required size */
	    int request = Math.max(2 * bits.length, unitsRequired);
	    long newBits[] = new long[request];
	    System.arraycopy(bits, 0, newBits, 0, unitsInUse);
	    bits = newBits;
	}
    }

    /**
     * Returns the "logical size" of this <code>BitSet</code>: the index of
     * the highest set bit in the <code>BitSet</code> plus one. Returns zero
     * if the <code>BitSet</code> contains no set bits.
     *
     * @return  the logical size of this <code>BitSet</code>.
     * @since   1.2
     */
    public int length() {
        if (unitsInUse == 0)
            return 0;

        int highestBit = (unitsInUse - 1) * 64;
	long highestUnit = bits[unitsInUse - 1];
	do {
            highestUnit = highestUnit >>> 1;
            highestBit++;
        } while(highestUnit > 0);
        return highestBit;
    }

    /**
     * Sets the bit specified by the index to <code>true</code>.
     *
     * @param     bitIndex   a bit index.
     * @exception IndexOutOfBoundsException if the specified index is negative.
     * @since     JDK1.0
     */
    public void set(int bitIndex) {
	if (bitIndex < 0)
	    throw new IndexOutOfBoundsException(Integer.toString(bitIndex));

        int unitIndex = unitIndex(bitIndex);
        int unitsRequired = unitIndex+1;

        if (unitsInUse < unitsRequired) {
            ensureCapacity(unitsRequired);
            bits[unitIndex] |= bit(bitIndex);
            unitsInUse = unitsRequired;
        } else {
            bits[unitIndex] |= bit(bitIndex);
        }            
    }

    /**
     * Sets the bit specified by the index to <code>false</code>.
     *
     * @param     bitIndex   the index of the bit to be cleared.
     * @exception IndexOutOfBoundsException if the specified index is negative.
     * @since     JDK1.0
     */
    public void clear(int bitIndex) {
	if (bitIndex < 0)
	    throw new IndexOutOfBoundsException(Integer.toString(bitIndex));
	int unitIndex = unitIndex(bitIndex);
	if (unitIndex >= unitsInUse)
	    return;

	bits[unitIndex] &= ~bit(bitIndex);
        if (bits[unitsInUse-1] == 0)
            recalculateUnitsInUse();
    }

    /**
     * Clears all of the bits in this <code>BitSet</code> whose corresponding
     * bit is set in the specified <code>BitSet</code>.
     *
     * @param     set the <code>BitSet</code> with which to mask this
     *            <code>BitSet</code>.
     * @since     1.2
     */
    public void andNot(BitSet set) {
        int unitsInCommon = Math.min(unitsInUse, set.unitsInUse);

	// perform logical (a & !b) on bits in common
        for (int i=0; i<unitsInCommon; i++) {
	    bits[i] &= ~set.bits[i];
        }

        recalculateUnitsInUse();
    }

    /**
     * Returns the value of the bit with the specified index. The value 
     * is <code>true</code> if the bit with the index <code>bitIndex</code> 
     * is currently set in this <code>BitSet</code> otherwise, the result 
     * is <code>false</code>.
     *
     * @param     bitIndex   the bit index.
     * @return    the value of the bit with the specified index.
     * @exception IndexOutOfBoundsException if the specified index is negative.
     */
    public boolean get(int bitIndex) {
	if (bitIndex < 0)
	    throw new IndexOutOfBoundsException(Integer.toString(bitIndex));

	boolean result = false;
	int unitIndex = unitIndex(bitIndex);
	if (unitIndex < unitsInUse)
	    result = ((bits[unitIndex] & bit(bitIndex)) != 0);

	return result;
    }

    /**
     * Performs a logical <b>AND</b> of this target bit set with the 
     * argument bit set. This bit set is modified so that each bit in it 
     * has the value <code>true</code> if and only if it both initially 
     * had the value <code>true</code> and the corresponding bit in the 
     * bit set argument also had the value <code>true</code>. 
     *
     * @param   set   a bit set. 
     */
    public void and(BitSet set) {
	if (this == set)
	    return;

	// perform logical AND on bits in common
	int oldUnitsInUse = unitsInUse;
	unitsInUse = Math.min(unitsInUse, set.unitsInUse);
        int i;
	for(i=0; i<unitsInUse; i++)
	    bits[i] &= set.bits[i];

	// clear out units no longer used
	for( ; i < oldUnitsInUse; i++)
	    bits[i] = 0;

        // Recalculate units in use if necessary
        if (unitsInUse > 0 && bits[unitsInUse - 1] == 0)
            recalculateUnitsInUse();
    }

    /**
     * Performs a logical <b>OR</b> of this bit set with the bit set 
     * argument. This bit set is modified so that a bit in it has the 
     * value <code>true</code> if and only if it either already had the 
     * value <code>true</code> or the corresponding bit in the bit set 
     * argument has the value <code>true</code>.
     *
     * @param   set   a bit set.
     */
    public void or(BitSet set) {
	if (this == set)
	    return;

	ensureCapacity(set.unitsInUse);

	// perform logical OR on bits in common
	int unitsInCommon = Math.min(unitsInUse, set.unitsInUse);
        int i;
	for(i=0; i<unitsInCommon; i++)
	    bits[i] |= set.bits[i];

	// copy any remaining bits
	for(; i<set.unitsInUse; i++)
	    bits[i] = set.bits[i];

        if (unitsInUse < set.unitsInUse)
            unitsInUse = set.unitsInUse;
    }

    /**
     * Performs a logical <b>XOR</b> of this bit set with the bit set 
     * argument. This bit set is modified so that a bit in it has the 
     * value <code>true</code> if and only if one of the following 
     * statements holds: 
     * <ul>
     * <li>The bit initially has the value <code>true</code>, and the 
     *     corresponding bit in the argument has the value <code>false</code>.
     * <li>The bit initially has the value <code>false</code>, and the 
     *     corresponding bit in the argument has the value <code>true</code>. 
     * </ul>
     *
     * @param   set   a bit set.
     */
    public void xor(BitSet set) {
        int unitsInCommon;

        if (unitsInUse >= set.unitsInUse) {
            unitsInCommon = set.unitsInUse;
        } else {
            unitsInCommon = unitsInUse;

            int newUnitsInUse = set.unitsInUse;
            ensureCapacity(newUnitsInUse);
            unitsInUse = newUnitsInUse;
        }

	// perform logical XOR on bits in common
        int i;
        for (i=0; i<unitsInCommon; i++)
	    bits[i] ^= set.bits[i];

	// copy any remaining bits
        for ( ; i<set.unitsInUse; i++)
            bits[i] = set.bits[i];

        recalculateUnitsInUse();
    }

    /**
     * Returns a hash code value for this bit set. The has code 
     * depends only on which bits have been set within this 
     * <code>BitSet</code>. The algorithm used to compute it may 
     * be described as follows.<p>
     * Suppose the bits in the <code>BitSet</code> were to be stored 
     * in an array of <code>long</code> integers called, say, 
     * <code>bits</code>, in such a manner that bit <code>k</code> is 
     * set in the <code>BitSet</code> (for nonnegative values of 
     * <code>k</code>) if and only if the expression 
     * <pre>((k>>6) < bits.length) && ((bits[k>>6] & (1L << (bit & 0x3F))) != 0)</pre>
     * is true. Then the following definition of the <code>hashCode</code> 
     * method would be a correct implementation of the actual algorithm:
     * <pre>
     * public synchronized int hashCode() {
     *      long h = 1234;
     *      for (int i = bits.length; --i >= 0; ) {
     *           h ^= bits[i] * (i + 1);
     *      }
     *      return (int)((h >> 32) ^ h);
     * }</pre>
     * Note that the hash code values change if the set of bits is altered.
     * <p>Overrides the <code>hashCode</code> method of <code>Object</code>.
     *
     * @return  a hash code value for this bit set.
     */
    public int hashCode() {
	long h = 1234;
	for (int i = bits.length; --i >= 0; )
            h ^= bits[i] * (i + 1);

	return (int)((h >> 32) ^ h);
    }
    
    /**
     * Returns the number of bits of space actually in use by this 
     * <code>BitSet</code> to represent bit values. 
     * The maximum element in the set is the size - 1st element.
     *
     * @return  the number of bits currently in this bit set.
     */
    public int size() {
	return bits.length << ADDRESS_BITS_PER_UNIT;
    }

    /**
     * Compares this object against the specified object.
     * The result is <code>true</code> if and only if the argument is 
     * not <code>null</code> and is a <code>Bitset</code> object that has 
     * exactly the same set of bits set to <code>true</code> as this bit 
     * set. That is, for every nonnegative <code>int</code> index <code>k</code>, 
     * <pre>((BitSet)obj).get(k) == this.get(k)</pre>
     * must be true. The current sizes of the two bit sets are not compared. 
     * <p>Overrides the <code>equals</code> method of <code>Object</code>.
     *
     * @param   obj   the object to compare with.
     * @return  <code>true</code> if the objects are the same;
     *          <code>false</code> otherwise.
     * @see     java.util.BitSet#size()
     */
    public boolean equals(Object obj) {
	if (!(obj instanceof BitSet))
	    return false;
	if (this == obj)
	    return true;

	BitSet set = (BitSet) obj;
	int minUnitsInUse = Math.min(unitsInUse, set.unitsInUse);

	// Check units in use by both BitSets
	for (int i = 0; i < minUnitsInUse; i++)
	    if (bits[i] != set.bits[i])
		return false;

	// Check any units in use by only one BitSet (must be 0 in other)
	if (unitsInUse > minUnitsInUse) {
	    for (int i = minUnitsInUse; i<unitsInUse; i++)
		if (bits[i] != 0)
		    return false;
	} else {
	    for (int i = minUnitsInUse; i<set.unitsInUse; i++)
		if (set.bits[i] != 0)
		    return false;
	}

	return true;
    }

    /**
     * Cloning this <code>BitSet</code> produces a new <code>BitSet</code> 
     * that is equal to it.
     * The clone of the bit set is another bit set that has exactly the 
     * same bits set to <code>true</code> as this bit set and the same 
     * current size. 
     * <p>Overrides the <code>clone</code> method of <code>Object</code>.
     *
     * @return  a clone of this bit set.
     * @see     java.util.BitSet#size()
     */
    public Object clone() {
	BitSet result = null;
	try {
	    result = (BitSet) super.clone();
	} catch (CloneNotSupportedException e) {
	    throw new InternalError();
	}
	result.bits = new long[bits.length];
	System.arraycopy(bits, 0, result.bits, 0, unitsInUse);
	return result;
    }

    /**
     * This override of readObject makes sure unitsInUse is set properly
     * when deserializing a bitset
     *
     */
    private void readObject(java.io.ObjectInputStream in)
        throws IOException, ClassNotFoundException {
        
        in.defaultReadObject();
        //assume maximum length then find real length
        //because recalculateUnitsInUse assumes maintenance
        //or reduction in logical size
        unitsInUse = bits.length;
        recalculateUnitsInUse();
    }

    /**
     * Returns a string representation of this bit set. For every index 
     * for which this <code>BitSet</code> contains a bit in the set 
     * state, the decimal representation of that index is included in 
     * the result. Such indeces aer listed in order from lowest to 
     * highest, separated by ",$nbsp;" (a comma and a space) and 
     * surrounded by braces, resulting in the usual mathematical 
     * notation for a set of integers.<p>
     * Overrides the <code>toString</code> method of <code>Object</code>.
     * <p>Example:
     * <pre>
     * BitSet drPepper = new BitSet();</pre>
     * Now <code>drPepper.toString()</code> returns "<code>{}</code>".<p>
     * <pre>
     * drPepper.set(2);</pre>
     * Now <code>drPepper.toString()</code> returns "<code>{2}</code>".<p>
     * <pre>
     * drPepper.set(4);
     * drPepper.set(10);</pre>
     * Now <code>drPepper.toString()</code> returns "<code>{2, 4, 10}</code>".
     *
     * @return  a string representation of this bit set.
     */
    public String toString() {
	int numBits = unitsInUse << ADDRESS_BITS_PER_UNIT;
	StringBuffer buffer = new StringBuffer(8*numBits + 2);
	String separator = "";
	buffer.append('{');

	for (int i = 0 ; i < numBits; i++) {
	    if (get(i)) {
		buffer.append(separator);
		separator = ", ";
	        buffer.append(i);
	    }
        }

	buffer.append('}');
	return buffer.toString();
    }
}