/*
Copyright (C) 1999 CERN - European Organization for Nuclear Research.
Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose 
is hereby granted without fee, provided that the above copyright notice appear in all copies and 
that both that copyright notice and this permission notice appear in supporting documentation. 
CERN makes no representations about the suitability of this software for any purpose. 
It is provided "as is" without expressed or implied warranty.
*/
package cern.colt.bitvector;

/**
 * Fixed sized (non resizable) bitvector.
 * Upon instance construction a bitvector is told to hold a fixed number of bits - it's size.
 * The size can be any number (need not be a power of 2 or so).
 * The bits of a BitVector are indexed by nonnegative integers. 
 * Any attempt to access a bit at an index<0 || index>=size() will throw an IndexOutOfBoundsException.
 * 

 * Individual indexed bits can be examined, set, or cleared.
 * Subranges can quickly be extracted, copied and replaced.
 * Quick iteration over subranges is provided by optimized internal iterators (forEach() methods).
 * One BitVector may be used to modify the contents of another 
 * BitVector through logical AND, OR, XOR and other similar operations.
 * 

 * All operations consider the bits 0..size()-1 and nothing else.
 * Operations involving two bitvectors (like AND, OR, XOR, etc.) will throw an IllegalArgumentException if the secondary bit vector has a size smaller than the receiver.
 * 

 * A BitVector is never automatically resized,
 * but it can manually be grown or shrinked via setSize(...).
 * 

 * For use cases that need to store several bits per information entity, quick accessors are provided that interpret subranges as 64 bit long integers.
 * 

 * Why this class? Fist, boolean[] take one byte per stored bit. This class takes one bit per stored bit.
 * Second, many applications find the semantics of java.util.BitSet not particularly helpful for their needs.
 * Third, operations working on all bits of a bitvector are extremely quick.
 * For example, on NT, Pentium Pro 200 Mhz, SunJDK1.2.2, java -classic, for two bitvectors A,B (both much larger than processor cache), the following results are obtained.
 * 

 * If you need extremely quick access to individual bits: Although getting and setting individual bits with methods get(...), set(...) and put(...)is quick, it is even quicker (but not safe) to use getQuick(...) and putQuick(...) or even QuickBitVector.
 * 

 * Note that this implementation is not synchronized.
 *
 * @author wolfgang.hoschek@cern.ch
 * @version 1.01, 11/10/99
 * @see     QuickBitVector
 * @see     BitMatrix
 * @see     java.util.BitSet
 */
public class BitVector extends cern.colt.PersistentObject {
	/*
	 * Bits 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.
	 */

	/**
	 * The bits of this object.  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).
	 *
	 * @serial
	 */
	protected long bits[];

	protected int nbits; //the size

	// IntProcedure for method indexOfFromTo(...)
	private class IndexProcedure implements cern.colt.function.IntProcedure {
			private int foundPos = -1;
			public boolean apply(int index) {
				foundPos = index; 
				return false;
			}
		}

/**
 * You normally need not use this method. Use this method only if performance is critical. 
 * Constructs a bit vector with the given backing bits and size.
 * WARNING: For efficiency reasons and to keep memory usage low, the array is not copied.
 * So if subsequently you modify the specified array directly via the [] operator, be sure you know what you're doing.
 *
 * 
A bitvector is modelled as a long array, i.e. long[] bits holds bits of a bitvector.
 * Each long value holds 64 bits.
 * The i-th 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).
 *
 * @throws IllegalArgumentException if size < 0 || size > bits.length*64.
 */
public BitVector (long[] bits, int size) {
	elements(bits,size);
}
/**
 * Constructs a bit vector that holds size bits. All bits are initially false.
 *
 * @param size the number of bits the bit vector shall have.
 * @throws IllegalArgumentException if size < 0.
 */
public BitVector(int size) {
	this(QuickBitVector.makeBitVector(size,1),size);
}
/**
 * Performs a logical AND of the receiver with another bit vector (A = A & B).
 * The receiver is modified so that a bit in it has the
 * value true if and only if it already had the 
 * value true and the corresponding bit in the other bit vector
 * argument has the value true.
 *
 * @param   other   a bit vector.
 * @throws IllegalArgumentException if size() > other.size().
 */
public void and(BitVector other) {
	if (this == other) return;
	checkSize(other);
	final long[] theBits = this.bits; // cached for speed.
	final long[] otherBits = other.bits; //cached for speed.
	for(int i=theBits.length; --i >= 0;) theBits[i] &= otherBits[i];
}
/**
 * Clears all of the bits in receiver whose corresponding
 * bit is set in the other bitvector (A = A \ B).
 * In other words, determines the difference (A=A\B) between two bitvectors.
 *
 * @param   other   a bitvector with which to mask the receiver.
 * @throws IllegalArgumentException if size() > other.size().
 */
public void andNot(BitVector other) {
	checkSize(other);
	final long[] theBits = this.bits; // cached for speed.
	final long[] otherBits = other.bits; //cached for speed.
	for(int i=theBits.length; --i >= 0;) theBits[i] &= ~otherBits[i];
}
/**
 * Returns the number of bits currently in the true state.
 * Optimized for speed. Particularly quick if the receiver is either sparse or dense.
 */
public int cardinality() {
	int cardinality=0;
	int fullUnits = numberOfFullUnits();
	final int bitsPerUnit = QuickBitVector.BITS_PER_UNIT;
	
	// determine cardinality on full units
	final long[] theBits=bits;
	for(int i=fullUnits; --i >= 0;) {
		long val = theBits[i];
		if (val == -1L) { // all bits set?
			cardinality += bitsPerUnit; 
		}
		else if (val != 0L) { // more than one bit set?
			for (int j=bitsPerUnit; --j >= 0; ) {
				if ((val & (1L << j)) != 0) cardinality++;
			}
		}
	}

	// determine cardinality on remaining partial unit, if any.
	for (int j=numberOfBitsInPartialUnit(); --j >= 0; ) {
		if ((theBits[fullUnits] & (1L << j)) != 0) cardinality++;
	}

	return cardinality;
}
/**
 * Checks if the given range is within the contained array's bounds.
 */
protected static void checkRangeFromTo(int from, int to, int theSize) {
	if (from<0 || from>to || to>=theSize)
		throw new IndexOutOfBoundsException("from: "+from+", to: "+to+", size="+theSize);
}
/**
 * Sanity check for operations requiring another bitvector with at least the same size.
 */
protected void checkSize(BitVector other) {
	if (nbits > other.size()) throw new IllegalArgumentException("Incompatible sizes: size="+nbits+", other.size()="+other.size());
}
/**
 * Clears all bits of the receiver.
 */
public void clear() {
	final long[] theBits = this.bits;
	for (int i = theBits.length; --i >= 0 ;) theBits[i] = 0L;
	
	//new LongArrayList(bits).fillFromToWith(0,size()-1,0L);
}
/**
 * Changes the bit with index bitIndex to the "clear" (false) state.
 *
 * @param     bitIndex   the index of the bit to be cleared.
 * @throws	IndexOutOfBoundsException if bitIndex<0 || bitIndex>=size()
 */
public void clear(int bitIndex) {
	if (bitIndex<0 || bitIndex>=nbits) throw new IndexOutOfBoundsException(String.valueOf(bitIndex));
	QuickBitVector.clear(bits, bitIndex);
}
/**
 * Cloning this BitVector produces a new BitVector 
 * that is equal to it.
 * The clone of the bit vector is another bit vector that has exactly the 
 * same bits set to true as this bit vector and the same 
 * current size, but independent state.
 *
 * @return  a deep copy of this bit vector.
 */
public Object clone() {
	BitVector clone = (BitVector) super.clone();
	if (this.bits != null) clone.bits = (long[]) this.bits.clone();
	return clone;
}
/**
 * Returns a deep copy of the receiver; calls clone() and casts the result.
 *
 * @return  a deep copy of the receiver.
 */
public BitVector copy() {
	return (BitVector) clone();
}
/**
 * You normally need not use this method. Use this method only if performance is critical. 
 * Returns the bit vector's backing bits.
 * WARNING: For efficiency reasons and to keep memory usage low, the array is not copied.
 * So if subsequently you modify the returned array directly via the [] operator, be sure you know what you're doing.
 *
 * 
A bitvector is modelled as a long array, i.e. long[] bits holds bits of a bitvector.
 * Each long value holds 64 bits.
 * The i-th 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).
 */
public long[] elements() {
	return bits;
}
/**
 * You normally need not use this method. Use this method only if performance is critical. 
 * Sets the bit vector's backing bits and size.
 * WARNING: For efficiency reasons and to keep memory usage low, the array is not copied.
 * So if subsequently you modify the specified array directly via the [] operator, be sure you know what you're doing.
 *
 * 
A bitvector is modelled as a long array, i.e. long[] bits holds bits of a bitvector.
 * Each long value holds 64 bits.
 * The i-th 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).
 *
 * @param bits the backing bits of the bit vector.
 * @param size the number of bits the bit vector shall hold.
 * @throws IllegalArgumentException if size < 0 || size > bits.length*64.
 */
public void elements(long[] bits, int size) {
	if (size<0 || size>bits.length*QuickBitVector.BITS_PER_UNIT) throw new IllegalArgumentException();
	this.bits = bits;
	this.nbits = size;
}
/**
 * Compares this object against the specified object.
 * The result is true if and only if the argument is 
 * not null and is a BitVector object
 * that has the same size as the receiver and 
 * the same bits set to true as the receiver.
 * That is, for every nonnegative int index k, 
 * 
((BitVector)obj).get(k) == this.get(k)

 * must be true.
 *
 * @param   obj   the object to compare with.
 * @return  true if the objects are the same;
 *          false otherwise.
 */
public boolean equals(Object obj) {
	if (obj == null || !(obj instanceof BitVector))
		return false;
	if (this == obj)
		return true;

	BitVector other = (BitVector) obj;
	if (size()!=other.size()) return false;

	int fullUnits = numberOfFullUnits();
	// perform logical comparison on full units
	for(int i=fullUnits; --i >= 0;)
		if (bits[i] != other.bits[i]) return false;

	// perform logical comparison on remaining bits
	int i=fullUnits*QuickBitVector.BITS_PER_UNIT;
	for (int times=numberOfBitsInPartialUnit(); --times >=0;) {
		if (get(i) != other.get(i)) return false;
		i++;
	}
		
	return true;	
}
/**
 * Applies a procedure to each bit index within the specified range that holds a bit in the given state.
 * Starts at index from, moves rightwards to to.
 * Useful, for example, if you want to copy bits into an image or somewhere else.
 * 

 * Optimized for speed. Particularly quick if one of the following conditions holds
 * 

 *
 * @param from the leftmost search position, inclusive.
 * @param to the rightmost search position, inclusive.
 * @param state element to search for.
 * @param procedure a procedure object taking as argument the current bit index. Stops iteration if the procedure returns false, otherwise continues. 
 * @return false if the procedure stopped before all elements where iterated over, true otherwise. 
 * @throws IndexOutOfBoundsException if (size()>0 && (from<0 || from>to || to>=size())).
 */
public boolean forEachIndexFromToInState(int from, int to, boolean state, cern.colt.function.IntProcedure procedure) {
	/*
	// this version is equivalent to the low level version below, but about 100 times slower for large ranges.
	if (nbits==0) return true;
	checkRangeFromTo(from, to, nbits);
	final long[] theBits = this.bits; // cached for speed
	int length=to-from+1;
	for (int i=from; --length >= 0; i++) {
		if (QuickBitVector.get(theBits,i)==state) {
			if (!function.apply(i)) return false;
		}
	}
	return true;
	*/
	

	/*
	 * This low level implementation exploits the fact that for any full unit one can determine in O(1)
	 * whether it contains at least one true bit,
	 * and whether it contains at least one false bit.
	 * Thus, 64 bits can often be skipped with one simple comparison if the vector is either sparse or dense.
	 *
	 * However, careful coding must be done for leading and/or trailing units which are not entirely contained in the query range.
	 */
	 
	if (nbits==0) return true;
	checkRangeFromTo(from, to, nbits);		
	//System.out.println("\n");
	//System.out.println(this);
	//System.out.println("from="+from+", to="+to+", bit="+state);

	// Cache some vars for speed.
	final long[] theBits = this.bits; 
	final int bitsPerUnit = QuickBitVector.BITS_PER_UNIT;

	// Prepare
	int fromUnit = QuickBitVector.unit(from);
	int toUnit = QuickBitVector.unit(to);
	int i = from; // current bitvector index

	// Iterate over the leading partial unit, if any.
	int bitIndex = QuickBitVector.offset(from);
	int partialWidth;
	if (bitIndex>0) { // There exists a leading partial unit.
		partialWidth = Math.min(to-from+1, bitsPerUnit - bitIndex);
		//System.out.println("partialWidth1="+partialWidth);
		for (; --partialWidth >= 0; i++) {
			if (QuickBitVector.get(theBits,i)==state) {
				if (!procedure.apply(i)) return false;
			}
		}
		fromUnit++; // leading partial unit is done.
	}

	if (i>to) return true; // done
	
	// If there is a trailing partial unit, then there is one full unit less to test.
	bitIndex = QuickBitVector.offset(to);
	if (bitIndex < bitsPerUnit-1) {
		toUnit--; // trailing partial unit needs to be tested extra.
		partialWidth = bitIndex + 1;
	}
	else {
		partialWidth = 0;
	}
	//System.out.println("partialWidth2="+partialWidth);

	// Iterate over all full units, if any.
	// (It does not matter that iterating over partial units is a little bit slow,
	// the only thing that matters is that iterating over full units is quick.)
	long comparator;
	if (state) comparator = 0L;
	else comparator = ~0L; // all 64 bits set
	
	//System.out.println("fromUnit="+fromUnit+", toUnit="+toUnit);
	for (int unit=fromUnit; unit<=toUnit; unit++) {
		long val = theBits[unit];
		if (val != comparator) { 
			// at least one element within current unit matches.
			// iterate over all bits within current unit.
			if (state) {
				for (int j=0, k=bitsPerUnit; --k >= 0; i++) { 
					if ((val & (1L << j++)) != 0L) { // is bit set?
						if (!procedure.apply(i)) return false;
					}
				}
			}
			else {
				for (int j=0, k=bitsPerUnit; --k >= 0; i++) { 
					if ((val & (1L << j++)) == 0L) { // is bit cleared?
						if (!procedure.apply(i)) return false;
					}
				}
			}
		}
		else {
			i += bitsPerUnit;
		}
	}

	//System.out.println("trail with i="+i);	

	// Iterate over trailing partial unit, if any.
	for (; --partialWidth >= 0; i++) {
		if (QuickBitVector.get(theBits,i)==state) {
			if (!procedure.apply(i)) return false;
		}
	}
		
	return true;	
}
/**
 * Returns from the bitvector the value of the bit with the specified index.
 * The value is true if the bit with the index bitIndex 
 * is currently set; otherwise, returns false.
 *
 * @param     bitIndex   the bit index.
 * @return    the value of the bit with the specified index.
 * @throws	IndexOutOfBoundsException if bitIndex<0 || bitIndex>=size()
 */
public boolean get(int bitIndex) {
	if (bitIndex<0 || bitIndex>=nbits) throw new IndexOutOfBoundsException(String.valueOf(bitIndex));
	return QuickBitVector.get(bits, bitIndex);
}
/**
 * Returns a long value representing bits of the receiver from index from to index to.
 * Bits are returned as a long value with the return value having bit 0 set to bit from, ..., bit to-from set to bit to.
 * All other bits of the return value are set to 0.
 * If to-from+1==0 then returns zero (0L).
 * @param from index of start bit (inclusive).
 * @param to index of end bit (inclusive).
 * @return the specified bits as long value.
 * @throws	IndexOutOfBoundsException if from<0 || from>=size() || to<0 || to>=size() || to-from+1<0 || to-from+1>64
 */
public long getLongFromTo(int from, int to) {
	int width = to-from+1;
	if (width==0) return 0L;
	if (from<0 || from>=nbits || to<0 || to>=nbits || width<0 || width>QuickBitVector.BITS_PER_UNIT) throw new IndexOutOfBoundsException("from:"+from+", to:"+to);
	return QuickBitVector.getLongFromTo(bits, from, to);
}
/**
 * Returns from the bitvector the value of the bit with the specified index; WARNING: Does not check preconditions.
 * The value is true if the bit with the index bitIndex 
 * is currently set; otherwise, returns false.
 *
 * 
Provided with invalid parameters this method may return invalid values without throwing any exception.
 * You should only use this method when you are absolutely sure that the index is within bounds.
 * Precondition (unchecked): bitIndex >= 0 && bitIndex < size().
 *
 * @param     bitIndex   the bit index.
 * @return    the value of the bit with the specified index.
 */
public boolean getQuick(int bitIndex) {
	return QuickBitVector.get(bits, bitIndex);
}
/**
 * Returns a hash code value for the receiver. The hash code 
 * depends only on which bits have been set within the receiver.
 * The algorithm used to compute it may 
 * be described as follows.

 * Suppose the bits in the receiver were to be stored 
 * in an array of long integers called, say, 
 * bits, in such a manner that bit k is 
 * set in the receiver (for nonnegative values of 
 * k) if and only if the expression 
 * 
((k>>6) < bits.length) && ((bits[k>>6] & (1L << (bit & 0x3F))) != 0)

 * is true. Then the following definition of the hashCode 
 * method would be a correct implementation of the actual algorithm:
 * 
 * public int hashCode() {
 *      long h = 1234;
 *      for (int i = bits.length; --i >= 0; ) {
 *           h ^= bits[i] * (i + 1);
 *      }
 *      return (int)((h >> 32) ^ h);
 * }

 * Note that the hash code values change if the set of bits is altered.
 *
 * @return  a hash code value for the receiver.
 */
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 index of the first occurrence of the specified
 * state. Returns -1 if the receiver does not contain this state.
 * Searches between from, inclusive and to, inclusive.
 * 

 * Optimized for speed. Preliminary performance (200Mhz Pentium Pro, JDK 1.2, NT): size=10^6, from=0, to=size-1, receiver contains matching state in the very end --> 0.002 seconds elapsed time.
 *
 * @param state state to search for.
 * @param from the leftmost search position, inclusive.
 * @param to the rightmost search position, inclusive.
 * @return  the index of the first occurrence of the element in the receiver; returns -1 if the element is not found.
 * @exception IndexOutOfBoundsException if (size()>0 && (from<0 || from>to || to>=size())).
 */
public int indexOfFromTo(int from, int to, boolean state) {
	IndexProcedure indexProcedure = new IndexProcedure();
	forEachIndexFromToInState(from,to,state,indexProcedure);
	return indexProcedure.foundPos; 
}
/**
 * Performs a logical NOT on the bits of the receiver (A = ~A).
 */
public void not() {
	final long[] theBits = this.bits;
	for (int i = theBits.length; --i >= 0 ;) theBits[i] = ~theBits[i];
}
/**
 * Returns the number of bits used in the trailing PARTIAL unit.
 * Returns zero if there is no such trailing partial unit.
 */
protected int numberOfBitsInPartialUnit() {
	return QuickBitVector.offset(nbits);
}
/**
 * Returns the number of units that are FULL (not PARTIAL).
 */
protected int numberOfFullUnits() {
	return QuickBitVector.unit(nbits);
}
/**
 * Performs a logical OR of the receiver with another bit vector (A = A | B).
 * The receiver is modified so that a bit in it has the
 * value true if and only if it either already had the 
 * value true or the corresponding bit in the other bit vector
 * argument has the value true.
 *
 * @param   other   a bit vector.
 * @throws IllegalArgumentException if size() > other.size().
 */
public void or(BitVector other) {
	if (this == other) return;
	checkSize(other);
	final long[] theBits = this.bits; // cached for speed.
	final long[] otherBits = other.bits; //cached for speed.
	for(int i=theBits.length; --i >= 0;) theBits[i] |= otherBits[i];
}
/**
 * Constructs and returns a new bit vector which is a copy of the given range.
 * The new bitvector has size()==to-from+1.
 *
 * @param from the start index within the receiver, inclusive.
 * @param to the end index within the receiver, inclusive.
 * @throws IndexOutOfBoundsException if size()>0 && (from<0 || from>to || to>=size())).
 */
public BitVector partFromTo(int from, int to) {
	if (nbits==0 || to==from-1) return new BitVector(0);
	checkRangeFromTo(from, to, nbits);

	int width = to-from+1;
	BitVector part = new BitVector(width);
	part.replaceFromToWith(0,width-1,this,from);
	return part;
}
/**
 * Sets the bit with index bitIndex to the state specified by value.
 *
 * @param     bitIndex   the index of the bit to be changed.
 * @param     value   the value to be stored in the bit.
 * @throws	IndexOutOfBoundsException if bitIndex<0 || bitIndex>=size()
 */
public void put(int bitIndex, boolean value) {	
	if (bitIndex<0 || bitIndex>=nbits) throw new IndexOutOfBoundsException(String.valueOf(bitIndex));
	if (value) 
		QuickBitVector.set(bits, bitIndex);
	else 
		QuickBitVector.clear(bits, bitIndex);
}
/**
 * Sets bits of the receiver from index from to index to to the bits of value.
 * Bit from is set to bit 0 of value, ..., bit to is set to bit to-from of value.
 * All other bits stay unaffected.
 * If to-from+1==0 then does nothing.
 * @param value the value to be copied into the receiver.
 * @param from index of start bit (inclusive).
 * @param to index of end bit (inclusive).
 * @throws	IndexOutOfBoundsException if from<0 || from>=size() || to<0 || to>=size() || to-from+1<0 || to-from+1>64.
 */
public void putLongFromTo(long value, int from, int to) {
	int width = to-from+1;
	if (width==0) return;
	if (from<0 || from>=nbits || to<0 || to>=nbits || width<0 || width>QuickBitVector.BITS_PER_UNIT) throw new IndexOutOfBoundsException("from:"+from+", to:"+to);
	QuickBitVector.putLongFromTo(bits, value, from, to);
}
/**
 * Sets the bit with index bitIndex to the state specified by value; WARNING: Does not check preconditions.
 *
 * 
Provided with invalid parameters this method may set invalid values without throwing any exception.
 * You should only use this method when you are absolutely sure that the index is within bounds.
 * Precondition (unchecked): bitIndex >= 0 && bitIndex < size().
 *
 * @param     bitIndex   the index of the bit to be changed.
 * @param     value   the value to be stored in the bit.
 */
public void putQuick(int bitIndex, boolean value) {	
	if (value) 
		QuickBitVector.set(bits, bitIndex);
	else 
		QuickBitVector.clear(bits, bitIndex);
}
/**
 * Replaces the bits of the receiver in the given range with the bits of another bit vector.
 * Replaces the range [from,to] with the contents of the range [sourceFrom,sourceFrom+to-from], all inclusive.
 * If source==this and the source and destination range intersect in an ambiguous way, then replaces as if using an intermediate auxiliary copy of the receiver.
 * 

 * Optimized for speed. Preliminary performance (200Mhz Pentium Pro, JDK 1.2, NT): replace 10^6 ill aligned bits --> 0.02 seconds elapsed time.
 *
 * @param from the start index within the receiver, inclusive.
 * @param to the end index within the receiver, inclusive.
 * @param source the source bitvector to copy from.
 * @param sourceFrom the start index within source, inclusive.
 * @throws IndexOutOfBoundsException if size()>0 && (from<0 || from>to || to>=size() || sourceFrom<0 || sourceFrom+to-from+1>source.size())).
 */
public void replaceFromToWith(int from, int to, BitVector source, int sourceFrom) {
	if (nbits==0 || to==from-1) return;
	checkRangeFromTo(from, to, nbits);
	int length=to-from+1;
	if (sourceFrom<0 || sourceFrom+length>source.size()) {
		throw new IndexOutOfBoundsException();
	}

	if (source.bits==this.bits && from<=sourceFrom && sourceFrom<=to) { // dangerous intersection
		source = source.copy();
	}
		
	final long[] theBits = this.bits; // cached for speed.
	final long[] sourceBits = source.bits; // cached for speed.

	/* 
	This version is equivalent to the version below but 20 times slower...
	for (int i=from; --length >= 0; i++, sourceFrom++) {
		QuickBitVector.put(theBits,i,QuickBitVector.get(sourceBits,sourceFrom));
	}
	*/

	// Low level implementation for speed.
	// This could be done even faster by implementing on even lower levels. But then the code would probably become a "don't touch" piece.
	final int width = to-from+1;
	final int blocks = QuickBitVector.unit(width); // width/64
	final int bitsPerUnit = QuickBitVector.BITS_PER_UNIT;
	final int bitsPerUnitMinusOne = bitsPerUnit-1;

	// copy entire 64 bit blocks, if any.
	for (int i=blocks; --i >=0; ) {
		long val = QuickBitVector.getLongFromTo(sourceBits,sourceFrom,sourceFrom+bitsPerUnitMinusOne);
		QuickBitVector.putLongFromTo(theBits,val,from,from+bitsPerUnitMinusOne);
		sourceFrom += bitsPerUnit;
		from += bitsPerUnit;
	}

	// copy trailing bits, if any.
	int offset = QuickBitVector.offset(width); //width%64
	long val = QuickBitVector.getLongFromTo(sourceBits,sourceFrom,sourceFrom+offset-1);
	QuickBitVector.putLongFromTo(theBits,val,from,from+offset-1);	
}
/**
 * Sets the bits in the given range to the state specified by value.
 * 

 * Optimized for speed. Preliminary performance (200Mhz Pentium Pro, JDK 1.2, NT): replace 10^6 ill aligned bits --> 0.002 seconds elapsed time.
 *
 * @param from the start index, inclusive.
 * @param to the end index, inclusive.
 * @param value the value to be stored in the bits of the range.
 * @throws IndexOutOfBoundsException if size()>0 && (from<0 || from>to || to>=size()).
 */
public void replaceFromToWith(int from, int to, boolean value) {
	if (nbits==0 || to==from-1) return;
	checkRangeFromTo(from, to, nbits);
	final long[] theBits = this.bits; // cached for speed
	
	int fromUnit = QuickBitVector.unit(from);
	int fromOffset = QuickBitVector.offset(from);
	int toUnit = QuickBitVector.unit(to);
	int toOffset = QuickBitVector.offset(to);
	int bitsPerUnit = QuickBitVector.BITS_PER_UNIT;

	long filler;
	if (value) filler = ~0L; 
	else filler = 0L;

	int bitIndex=from;
	if (fromUnit==toUnit) { // only one unit to do
		QuickBitVector.putLongFromTo(theBits,filler,bitIndex,bitIndex+to-from);
		//slower: for (; bitIndex<=to; ) QuickBitVector.put(theBits,bitIndex++,value);
		return;
	}

	// treat leading partial unit, if any.
	if (fromOffset > 0) { // fix by Olivier Janssens
		QuickBitVector.putLongFromTo(theBits,filler,bitIndex,bitIndex+bitsPerUnit-fromOffset);
		bitIndex += bitsPerUnit-fromOffset+1;
		/* slower:
		for (int i=bitsPerUnit-fromOffset; --i >= 0; ) {
			QuickBitVector.put(theBits,bitIndex++,value);
		}*/	
		fromUnit++;
	}	
	if (toOffset= 0; ) {
			QuickBitVector.put(theBits,bitIndex++,value);
		}*/
	}	
}
/**
 * Changes the bit with index bitIndex to the "set" (true) state.
 *
 * @param     bitIndex   the index of the bit to be set.
 * @throws	IndexOutOfBoundsException if bitIndex<0 || bitIndex>=size()
 */
public void set(int bitIndex) {
	if (bitIndex<0 || bitIndex>=nbits) throw new IndexOutOfBoundsException(String.valueOf(bitIndex));
	QuickBitVector.set(bits, bitIndex);
}
/**
 * Shrinks or expands the receiver so that it holds newSize bits.
 * If the receiver is expanded, additional false bits are added to the end.
 * If the receiver is shrinked, all bits between the old size and the new size are lost; their memory is subject to garbage collection.
 * (This method introduces a new backing array of elements. WARNING: if you have more than one BitVector or BitMatrix sharing identical backing elements, be sure you know what you are doing.)
 *
 * @param newSize the number of bits the bit vector shall have.
 * @throws IllegalArgumentException if size < 0.
 */
public void setSize(int newSize) {
	if (newSize!=size()) {
		BitVector newVector = new BitVector(newSize);
		newVector.replaceFromToWith(0,Math.min(size(),newSize)-1,this,0);
		elements(newVector.elements(),newSize);
	}
}
/**
 * Returns the size of the receiver.
 */
public int size() {
	return nbits;
}
/**
 * Returns a string representation of the receiver. For every index 
 * for which the receiver contains a bit in the "set" (true)
 * state, the decimal representation of that index is included in 
 * the result. Such indeces are listed in order from lowest to 
 * highest, separated by ", " (a comma and a space) and 
 * surrounded by braces.
 *
 * @return  a string representation of this bit vector.
 */
public String toString() {
	StringBuffer buffer = new StringBuffer(nbits);
	String separator = "";
	buffer.append('{');

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

	buffer.append('}');
	return buffer.toString();
}
/**
 * Performs a logical XOR of the receiver with another bit vector (A = A ^ B).
 * The receiver is modified so that a bit in it has the
 * value true if and only if one of the following statements holds:
 * 

 *
 * @param   other   a bit vector.
 * @throws IllegalArgumentException if size() > other.size().
 */
public void xor(BitVector other) {
	checkSize(other);
	final long[] theBits = this.bits; // cached for speed.
	final long[] otherBits = other.bits; //cached for speed.
	for(int i=theBits.length; --i >= 0;) theBits[i] ^= otherBits[i];
}
}

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