package org.apache.lucene.util;
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2001 The Apache Software Foundation. All rights
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* if any, must include the following acknowledgment:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgment may appear in the software itself,
* if and wherever such third-party acknowledgments normally appear.
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* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*/
import java.io.IOException;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.InputStream;
import org.apache.lucene.store.OutputStream;
/** Optimized implementation of a vector of bits. This is more-or-less like
java.util.BitSet, but also includes the following:
<UL>
<LI>a count() method, which efficiently computes the number of one bits;</LI>
<LI>optimized read from and write to disk;</LI>
<LI>inlinable get() method;</LI>
</UL>
*/
public final class BitVector {
/** This is public just so that methods will inline. Please don't touch.*/
public byte[] bits;
private int size;
private int count = -1;
/** Constructs a vector capable of holding <code>n</code> bits. */
public BitVector(int n) {
size = n;
bits = new byte[(size >> 3) + 1];
}
/** Sets the value of <code>bit</code> to one. */
public final void set(int bit) {
bits[bit >> 3] |= 1 << (bit & 7);
count = -1;
}
/** Sets the value of <code>bit</code> to zero. */
public final void clear(int bit) {
bits[bit >> 3] &= ~(1 << (bit & 7));
count = -1;
}
/** Returns <code>true</code> if <code>bit</code> is one and
<code>false</code> if it is zero. */
public final boolean get(int bit) {
return (bits[bit >> 3] & (1 << (bit & 7))) != 0;
}
/** Returns the number of bits in this vector. This is also one greater than
the number of the largest valid bit number. */
public final int size() {
return size;
}
/** Returns the total number of one bits in this vector. This is efficiently
computed and cached, so that, if the vector is not changed, no
recomputation is done for repeated calls. */
public final int count() {
if (count == -1) {
int c = 0;
int end = bits.length;
for (int i = 0; i < end; i++)
c += BYTE_COUNTS[bits[i] & 0xFF]; // sum bits per byte
count = c;
}
return count;
}
private static final byte[] BYTE_COUNTS = { // table of bits/byte
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
};
/** Writes this vector to the file <code>name</code> in Directory
<code>d</code>, in a format that can be read by the constructor {@link
#BitVector(Directory, String)}. */
public final void write(Directory d, String name) throws IOException {
OutputStream output = d.createFile(name);
try {
output.writeInt(size()); // write size
output.writeInt(count()); // write count
output.writeBytes(bits, bits.length); // write bits
} finally {
output.close();
}
}
/** Constructs a bit vector from the file <code>name</code> in Directory
<code>d</code>, as written by the {@link #write} method.
*/
public BitVector(Directory d, String name) throws IOException {
InputStream input = d.openFile(name);
try {
size = input.readInt(); // read size
count = input.readInt(); // read count
bits = new byte[(size >> 3) + 1]; // allocate bits
input.readBytes(bits, 0, bits.length); // read bits
} finally {
input.close();
}
}
}