* @status updated to 1.4
*/
public class BitSet implements Cloneable, Serializable
{
/**
* Compatible with JDK 1.0.
*/
private static final long serialVersionUID = 7997698588986878753L;
/**
* A common mask.
*/
private static final int LONG_MASK = 0x3f;
/**
* The actual bits.
* @serial the i'th bit is in bits[i/64] at position i%64 (where position
* 0 is the least significant).
*/
private long[] bits;
/**
* Create a new empty bit set. All bits are initially false.
*/
public BitSet()
{
this(64);
}
/**
* Create a new empty bit set, with a given size. This
* constructor reserves enough space to represent the integers
* from 0 to nbits-1.
*
* @param nbits the initial size of the bit set
* @throws NegativeArraySizeException if nbits < 0
*/
public BitSet(int nbits)
{
int length = nbits >>> 6;
if ((nbits & LONG_MASK) != 0)
++length;
bits = new long[length];
}
/**
* Performs the logical AND operation on this bit set and the
* given set. This means it builds the intersection
* of the two sets. The result is stored into this bit set.
*
* @param set the second bit set
* @throws NullPointerException if set is null
*/
public void and(BitSet bs)
{
int max = Math.min(bits.length, bs.bits.length);
int i;
for (i = 0; i < max; ++i)
bits[i] &= bs.bits[i];
while (i < bits.length)
bits[i++] = 0;
}
/**
* Performs the logical AND operation on this bit set and the
* complement of the given set. This means it
* selects every element in the first set, that isn't in the
* second set. The result is stored into this bit set.
*
* @param set the second bit set
* @throws NullPointerException if set is null
* @since 1.2
*/
public void andNot(BitSet bs)
{
int i = Math.min(bits.length, bs.bits.length);
while (--i >= 0)
bits[i] &= ~bs.bits[i];
}
/**
* Returns the number of bits set to true.
*
* @return the number of true bits
* @since 1.4
*/
public int cardinality()
{
int card = 0;
for (int i = bits.length - 1; i >= 0; i--)
{
long a = bits[i];
// Take care of common cases.
if (a == 0)
continue;
if (a == -1)
{
card += 64;
continue;
}
// Successively collapse alternating bit groups into a sum.
a = ((a >> 1) & 0x5555555555555555L) + (a & 0x5555555555555555L);
a = ((a >> 2) & 0x3333333333333333L) + (a & 0x3333333333333333L);
int b = (int) ((a >>> 32) + a);
b = ((b >> 4) & 0x0f0f0f0f) + (b & 0x0f0f0f0f);
b = ((b >> 8) & 0x00ff00ff) + (b & 0x00ff00ff);
card += ((b >> 16) & 0x0000ffff) + (b & 0x0000ffff);
}
return card;
}
/**
* Sets all bits in the set to false.
*
* @since 1.4
*/
public void clear()
{
Arrays.fill(bits, 0);
}
/**
* Removes the integer bitIndex from this set. That is
* the corresponding bit is cleared. If the index is not in the set,
* this method does nothing.
*
* @param bitIndex a non-negative integer
* @throws IndexOutOfBoundsException if bitIndex < 0
*/
public void clear(int pos)
{
int offset = pos >>> 6;
ensure(offset);
// ArrayIndexOutOfBoundsException subclasses IndexOutOfBoundsException,
// so we'll just let that be our exception.
bits[offset] &= ~(1L << pos);
}
/**
* Sets the bits between from (inclusive) and to (exclusive) to false.
*
* @param from the start range (inclusive)
* @param to the end range (exclusive)
* @throws IndexOutOfBoundsException if from < 0 || from > to
* @since 1.4
*/
public void clear(int from, int to)
{
if (from < 0 || from > to)
throw new IndexOutOfBoundsException();
if (from == to)
return;
int lo_offset = from >>> 6;
int hi_offset = to >>> 6;
ensure(hi_offset);
if (lo_offset == hi_offset)
{
bits[hi_offset] &= ((1L << from) - 1) | (-1L << to);
return;
}
bits[lo_offset] &= (1L << from) - 1;
bits[hi_offset] &= -1L << to;
for (int i = lo_offset + 1; i < hi_offset; i++)
bits[i] = 0;
}
/**
* Create a clone of this bit set, that is an instance of the same
* class and contains the same elements. But it doesn't change when
* this bit set changes.
*
* @return the clone of this object.
*/
public Object clone()
{
try
{
BitSet bs = (BitSet) super.clone();
bs.bits = (long[]) bits.clone();
return bs;
}
catch (CloneNotSupportedException e)
{
// Impossible to get here.
return null;
}
}
/**
* Returns true if the obj is a bit set that contains
* exactly the same elements as this bit set, otherwise false.
*
* @param obj the object to compare to
* @return true if obj equals this bit set
*/
public boolean equals(Object obj)
{
if (!(obj instanceof BitSet))
return false;
BitSet bs = (BitSet) obj;
int max = Math.min(bits.length, bs.bits.length);
int i;
for (i = 0; i < max; ++i)
if (bits[i] != bs.bits[i])
return false;
// If one is larger, check to make sure all extra bits are 0.
for (int j = i; j < bits.length; ++j)
if (bits[j] != 0)
return false;
for (int j = i; j < bs.bits.length; ++j)
if (bs.bits[j] != 0)
return false;
return true;
}
/**
* Sets the bit at the index to the opposite value.
*
* @param index the index of the bit
* @throws IndexOutOfBoundsException if index is negative
* @since 1.4
*/
public void flip(int index)
{
int offset = index >>> 6;
ensure(offset);
// ArrayIndexOutOfBoundsException subclasses IndexOutOfBoundsException,
// so we'll just let that be our exception.
bits[offset] ^= 1L << index;
}
/**
* Sets a range of bits to the opposite value.
*
* @param from the low index (inclusive)
* @param to the high index (exclusive)
* @throws IndexOutOfBoundsException if from > to || from < 0
* @since 1.4
*/
public void flip(int from, int to)
{
if (from < 0 || from > to)
throw new IndexOutOfBoundsException();
if (from == to)
return;
int lo_offset = from >>> 6;
int hi_offset = to >>> 6;
ensure(hi_offset);
if (lo_offset == hi_offset)
{
bits[hi_offset] ^= (-1L << from) & ((1L << to) - 1);
return;
}
bits[lo_offset] ^= -1L << from;
bits[hi_offset] ^= (1L << to) - 1;
for (int i = lo_offset + 1; i < hi_offset; i++)
bits[i] ^= -1;
}
/**
* Returns true if the integer bitIndex is in this bit
* set, otherwise false.
*
* @param pos a non-negative integer
* @return the value of the bit at the specified index
* @throws IndexOutOfBoundsException if the index is negative
*/
public boolean get(int pos)
{
int offset = pos >>> 6;
if (offset >= bits.length)
return false;
// ArrayIndexOutOfBoundsException subclasses IndexOutOfBoundsException,
// so we'll just let that be our exception.
return (bits[offset] & (1L << pos)) != 0;
}
/**
* Returns a new BitSet composed of a range of bits from
* this one.
*
* @param from the low index (inclusive)
* @param to the high index (exclusive)
* @throws IndexOutOfBoundsException if from > to || from < 0
* @since 1.4
*/
public BitSet get(int from, int to)
{
if (from < 0 || from > to)
throw new IndexOutOfBoundsException();
BitSet bs = new BitSet(to - from);
int lo_offset = from >>> 6;
if (lo_offset >= bits.length)
return bs;
int lo_bit = from & LONG_MASK;
int hi_offset = to >>> 6;
if (lo_bit == 0)
{
int len = Math.min(hi_offset - lo_offset + 1, bits.length - lo_offset);
System.arraycopy(bits, lo_offset, bs.bits, 0, len);
if (hi_offset < bits.length)
bs.bits[hi_offset - lo_offset] &= (1L << to) - 1;
return bs;
}
int len = Math.min(hi_offset, bits.length - 1);
int reverse = ~lo_bit;
int i;
for (i = 0; lo_offset < len; lo_offset++, i++)
bs.bits[i] = ((bits[lo_offset] >>> lo_bit)
| (bits[lo_offset + 1] << reverse));
if ((to & LONG_MASK) > lo_bit)
bs.bits[i++] = bits[lo_offset] >>> lo_bit;
if (hi_offset < bits.length)
bs.bits[i - 1] &= (1L << (to - from)) - 1;
return bs;
}
/**
* Returns a hash code value for this bit set. The hash code of
* two bit sets containing the same integers is identical. The algorithm
* used to compute it is as follows:
*
* Suppose the bits in the BitSet were to be stored in an array of
* long integers called bits, in such a manner that
* bit k is set in the BitSet (for non-negative values
* of k) if and only if
*
*
* ((k/64) < bits.length) && ((bits[k/64] & (1L << (bit % 64))) != 0)
*
*
* 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-1; i>=0; i--) {
* h ^= bits[i] * (i + 1);
* }
* return (int)((h >> 32) ^ h);
* }
*
*
* Note that the hash code values changes, if the set is changed.
*
* @return the hash code value for this bit set.
*/
public int hashCode()
{
long h = 1234;
for (int i = bits.length; i > 0; )
h ^= i * bits[--i];
return (int) ((h >> 32) ^ h);
}
/**
* Returns true if the specified BitSet and this one share at least one
* common true bit.
*
* @param set the set to check for intersection
* @return true if the sets intersect
* @throws NullPointerException if set is null
* @since 1.4
*/
public boolean intersects(BitSet set)
{
int i = Math.min(bits.length, set.bits.length);
while (--i >= 0)
if ((bits[i] & set.bits[i]) != 0)
return true;
return false;
}
/**
* Returns true if this set contains no true bits.
*
* @return true if all bits are false
* @since 1.4
*/
public boolean isEmpty()
{
for (int i = bits.length - 1; i >= 0; i--)
if (bits[i] != 0)
return false;
return true;
}
/**
* Returns the logical number of bits actually used by this bit
* set. It returns the index of the highest set bit plus one.
* Note that this method doesn't return the number of set bits.
*
* @return the index of the highest set bit plus one.
*/
public int length()
{
// Set i to highest index that contains a non-zero value.
int i;
for (i = bits.length - 1; i >= 0 && bits[i] == 0; --i)
;
// if i < 0 all bits are cleared.
if (i < 0)
return 0;
// Now determine the exact length.
long b = bits[i];
int len = (i + 1) * 64;
// b >= 0 checks if the highest bit is zero.
while (b >= 0)
{
--len;
b <<= 1;
}
return len;
}
/**
* Returns the index of the next false bit, from the specified bit
* (inclusive).
*
* @param from the start location
* @return the first false bit
* @throws IndexOutOfBoundsException if from is negative
* @since 1.4
*/
public int nextClearBit(int from)
{
int offset = from >>> 6;
long mask = 1L << from;
while (offset < bits.length)
{
// ArrayIndexOutOfBoundsException subclasses IndexOutOfBoundsException,
// so we'll just let that be our exception.
long h = bits[offset];
do
{
if ((h & mask) == 0)
return from;
mask <<= 1;
from++;
}
while (mask != 0);
mask = 1;
offset++;
}
return from;
}
/**
* Returns the index of the next true bit, from the specified bit
* (inclusive). If there is none, -1 is returned. You can iterate over
* all true bits with this loop:
*
* for (int i = bs.nextSetBit(0); i >= 0; i = bs.nextSetBit(i + 1))
* { // operate on i here }
*
*
* @param from the start location
* @return the first true bit, or -1
* @throws IndexOutOfBoundsException if from is negative
* @since 1.4
*/
public int nextSetBit(int from)
{
int offset = from >>> 6;
long mask = 1L << from;
while (offset < bits.length)
{
// ArrayIndexOutOfBoundsException subclasses IndexOutOfBoundsException,
// so we'll just let that be our exception.
long h = bits[offset];
do
{
if ((h & mask) != 0)
return from;
mask <<= 1;
from++;
}
while (mask != 0);
mask = 1;
offset++;
}
return -1;
}
/**
* Performs the logical OR operation on this bit set and the
* given set. This means it builds the union
* of the two sets. The result is stored into this bit set, which
* grows as necessary.
*
* @param bs the second bit set
* @throws NullPointerException if bs is null
*/
public void or(BitSet bs)
{
ensure(bs.bits.length - 1);
for (int i = bs.bits.length - 1; i >= 0; i--)
bits[i] |= bs.bits[i];
}
/**
* Add the integer bitIndex to this set. That is
* the corresponding bit is set to true. If the index was already in
* the set, this method does nothing. The size of this structure
* is automatically increased as necessary.
*
* @param pos a non-negative integer.
* @throws IndexOutOfBoundsException if pos is negative
*/
public void set(int pos)
{
int offset = pos >>> 6;
ensure(offset);
// ArrayIndexOutOfBoundsException subclasses IndexOutOfBoundsException,
// so we'll just let that be our exception.
bits[offset] |= 1L << pos;
}
/**
* Sets the bit at the given index to the specified value. The size of
* this structure is automatically increased as necessary.
*
* @param index the position to set
* @param value the value to set it to
* @throws IndexOutOfBoundsException if index is negative
* @since 1.4
*/
public void set(int index, boolean value)
{
if (value)
set(index);
else
clear(index);
}
/**
* Sets the bits between from (inclusive) and to (exclusive) to true.
*
* @param from the start range (inclusive)
* @param to the end range (exclusive)
* @throws IndexOutOfBoundsException if from < 0 || from > to
* @since 1.4
*/
public void set(int from, int to)
{
if (from < 0 || from > to)
throw new IndexOutOfBoundsException();
if (from == to)
return;
int lo_offset = from >>> 6;
int hi_offset = to >>> 6;
ensure(hi_offset);
if (lo_offset == hi_offset)
{
bits[hi_offset] |= (-1L << from) & ((1L << to) - 1);
return;
}
bits[lo_offset] |= -1L << from;
bits[hi_offset] |= (1L << to) - 1;
for (int i = lo_offset + 1; i < hi_offset; i++)
bits[i] = -1;
}
/**
* Sets the bits between from (inclusive) and to (exclusive) to the
* specified value.
*
* @param from the start range (inclusive)
* @param to the end range (exclusive)
* @param value the value to set it to
* @throws IndexOutOfBoundsException if from < 0 || from > to
* @since 1.4
*/
public void set(int from, int to, boolean value)
{
if (value)
set(from, to);
else
clear(from, to);
}
/**
* Returns the number of bits actually used by this bit set. Note
* that this method doesn't return the number of set bits, and that
* future requests for larger bits will make this automatically grow.
*
* @return the number of bits currently used.
*/
public int size()
{
return bits.length * 64;
}
/**
* Returns the string representation of this bit set. This
* consists of a comma separated list of the integers in this set
* surrounded by curly braces. There is a space after each comma.
* A sample string is thus "{1, 3, 53}".
* @return the string representation.
*/
public String toString()
{
StringBuffer r = new StringBuffer("{");
boolean first = true;
for (int i = 0; i < bits.length; ++i)
{
long bit = 1;
long word = bits[i];
if (word == 0)
continue;
for (int j = 0; j < 64; ++j)
{
if ((word & bit) != 0)
{
if (! first)
r.append(", ");
r.append(64 * i + j);
first = false;
}
bit <<= 1;
}
}
return r.append("}").toString();
}
/**
* Performs the logical XOR operation on this bit set and the
* given set. This means it builds the symmetric
* remainder of the two sets (the elements that are in one set,
* but not in the other). The result is stored into this bit set,
* which grows as necessary.
*
* @param bs the second bit set
* @throws NullPointerException if bs is null
*/
public void xor(BitSet bs)
{
ensure(bs.bits.length - 1);
for (int i = bs.bits.length - 1; i >= 0; i--)
bits[i] ^= bs.bits[i];
}
/**
* Make sure the vector is big enough.
*
* @param lastElt the size needed for the bits array
*/
private final void ensure(int lastElt)
{
if (lastElt >= bits.length)
{
long[] nd = new long[lastElt + 1];
System.arraycopy(bits, 0, nd, 0, bits.length);
bits = nd;
}
}
}