/*
* This file is part of FFMQ.
*
* FFMQ is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* FFMQ 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with FFMQ; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package net.timewalker.ffmq4.utils;
import java.util.BitSet;
/**
* <p>Simplistic version of the jdk {@link BitSet}</p>
* No bound-checking, internal capacity must be extended explicitely.
*/
public final class FastBitSet
{
/*
* BitSets are packed into arrays of "words." Currently a word is
* a long, which consists of 64 bits, requiring 6 address bits.
* The choice of word size is determined purely by performance concerns.
*/
private final static int ADDRESS_BITS_PER_WORD = 6;
private final static int BITS_PER_WORD = 1 << ADDRESS_BITS_PER_WORD;
// Storage
private long[] words;
/**
* Creates a bit set of size nbits
* @param nbits the initial size of the bit set.
*/
public FastBitSet(int nbits)
{
words = new long[wordIndex(nbits - 1) + 1];
}
/**
* Given a bit index, return word index containing it.
*/
private static int wordIndex(int bitIndex)
{
return bitIndex >> ADDRESS_BITS_PER_WORD;
}
/**
* Ensures that the BitSet can hold enough bits.
* @param requiredBits the required number of bits.
*/
public void ensureCapacity(int requiredBits)
{
int requiredWords = wordIndex(requiredBits - 1) + 1;
if (words.length < requiredWords)
{
long[] newWords = new long[requiredWords];
System.arraycopy(words, 0, newWords, 0, words.length);
words = newWords;
}
}
/**
* Sets the bit at the specified index to the complement of its
* current value.
* @param bitIndex the index of the bit to flip
* @return true if the bit was set to, false if it was unset
*/
public boolean flip(int bitIndex)
{
int wordIndex = wordIndex(bitIndex);
words[wordIndex] ^= (1L << bitIndex);
return ((words[wordIndex] & (1L << bitIndex)) != 0);
}
/**
* Sets the bit at the specified index to <code>true</code>.
* @param bitIndex a bit index.
*/
public void set(int bitIndex)
{
int wordIndex = wordIndex(bitIndex);
words[wordIndex] |= (1L << bitIndex); // Restores invariants
}
/**
* Sets the bit specified by the index to <code>false</code>.
* @param bitIndex the index of the bit to be cleared.
*/
public void clear(int bitIndex)
{
int wordIndex = wordIndex(bitIndex);
words[wordIndex] &= ~(1L << bitIndex);
}
/**
* Sets all of the bits in this BitSet to <code>false</code>.
*/
public void clear()
{
for (int i = 0 ; i < words.length ; i++)
words[i] = 0;
}
/**
* 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.
*/
public boolean get(int bitIndex)
{
int wordIndex = wordIndex(bitIndex);
return ((words[wordIndex] & (1L << bitIndex)) != 0);
}
/**
* 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 words.length * BITS_PER_WORD;
}
}