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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cassandra.utils.obs;
import java.util.Arrays;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.cassandra.db.TypeSizes;
import org.apache.cassandra.utils.concurrent.Ref;
/**
*
* An "open" BitSet implementation that allows direct access to the arrays of words
* storing the bits. Derived from Lucene's OpenBitSet, but with a paged backing array
* (see bits delaration, below).
*
*
* Unlike java.util.bitset, the fact that bits are packed into an array of longs
* is part of the interface. This allows efficient implementation of other algorithms
* by someone other than the author. It also allows one to efficiently implement
* alternate serialization or interchange formats.
*
*
* OpenBitSet is faster than java.util.BitSet in most operations
* and *much* faster at calculating cardinality of sets and results of set operations.
* It can also handle sets of larger cardinality (up to 64 * 2**32-1)
*
*
* The goals of OpenBitSet are the fastest implementation possible, and
* maximum code reuse. Extra safety and encapsulation
* may always be built on top, but if that's built in, the cost can never be removed (and
* hence people re-implement their own version in order to get better performance).
* If you want a "safe", totally encapsulated (and slower and limited) BitSet
* class, use java.util.BitSet.
*
*/
public class OpenBitSet implements IBitSet
{
/**
* We break the bitset up into multiple arrays to avoid promotion failure caused by attempting to allocate
* large, contiguous arrays (CASSANDRA-2466). All sub-arrays but the last are uniformly PAGE_SIZE words;
* to avoid waste in small bloom filters (of which Cassandra has many: one per row) the last sub-array
* is sized to exactly the remaining number of words required to achieve the desired set size (CASSANDRA-3618).
*/
private final long[][] bits;
private int wlen; // number of words (elements) used in the array
private final int pageCount;
private static final int PAGE_SIZE = 4096;
/**
* Constructs an OpenBitSet large enough to hold numBits.
* @param numBits
*/
public OpenBitSet(long numBits)
{
wlen = (int) bits2words(numBits);
int lastPageSize = wlen % PAGE_SIZE;
int fullPageCount = wlen / PAGE_SIZE;
pageCount = fullPageCount + (lastPageSize == 0 ? 0 : 1);
bits = new long[pageCount][];
for (int i = 0; i < fullPageCount; ++i)
bits[i] = new long[PAGE_SIZE];
if (lastPageSize != 0)
bits[bits.length - 1] = new long[lastPageSize];
}
public OpenBitSet() {
this(64);
}
/**
* @return the pageSize
*/
public int getPageSize()
{
return PAGE_SIZE;
}
public int getPageCount()
{
return pageCount;
}
public long[] getPage(int pageIdx)
{
return bits[pageIdx];
}
/** Returns the current capacity in bits (1 greater than the index of the last bit) */
public long capacity() { return ((long)wlen) << 6; }
@Override
public long offHeapSize()
{
return 0;
}
public void addTo(Ref.IdentityCollection identities)
{
}
/**
* Returns the current capacity of this set. Included for
* compatibility. This is *not* equal to {@link #cardinality}
*/
public long size() {
return capacity();
}
// @Override -- not until Java 1.6
public long length() {
return capacity();
}
/** Returns true if there are no set bits */
public boolean isEmpty() { return cardinality()==0; }
/** Expert: gets the number of longs in the array that are in use */
public int getNumWords() { return wlen; }
/**
* Returns true or false for the specified bit index.
* The index should be less than the OpenBitSet size
*/
public boolean get(int index) {
int i = index >> 6; // div 64
// signed shift will keep a negative index and force an
// array-index-out-of-bounds-exception, removing the need for an explicit check.
int bit = index & 0x3f; // mod 64
long bitmask = 1L << bit;
// TODO perfectionist one can implement this using bit operations
return (bits[i / PAGE_SIZE][i % PAGE_SIZE ] & bitmask) != 0;
}
/**
* Returns true or false for the specified bit index.
* The index should be less than the OpenBitSet size.
*/
public boolean get(long index) {
int i = (int)(index >> 6); // div 64
int bit = (int)index & 0x3f; // mod 64
long bitmask = 1L << bit;
// TODO perfectionist one can implement this using bit operations
return (bits[i / PAGE_SIZE][i % PAGE_SIZE ] & bitmask) != 0;
}
/**
* Sets the bit at the specified index.
* The index should be less than the OpenBitSet size.
*/
public void set(long index) {
int wordNum = (int)(index >> 6);
int bit = (int)index & 0x3f;
long bitmask = 1L << bit;
bits[ wordNum / PAGE_SIZE ][ wordNum % PAGE_SIZE ] |= bitmask;
}
/**
* Sets the bit at the specified index.
* The index should be less than the OpenBitSet size.
*/
public void set(int index) {
int wordNum = index >> 6; // div 64
int bit = index & 0x3f; // mod 64
long bitmask = 1L << bit;
bits[ wordNum / PAGE_SIZE ][ wordNum % PAGE_SIZE ] |= bitmask;
}
/**
* clears a bit.
* The index should be less than the OpenBitSet size.
*/
public void clear(int index) {
int wordNum = index >> 6;
int bit = index & 0x03f;
long bitmask = 1L << bit;
bits[wordNum / PAGE_SIZE][wordNum % PAGE_SIZE] &= ~bitmask;
// hmmm, it takes one more instruction to clear than it does to set... any
// way to work around this? If there were only 63 bits per word, we could
// use a right shift of 10111111...111 in binary to position the 0 in the
// correct place (using sign extension).
// Could also use Long.rotateRight() or rotateLeft() *if* they were converted
// by the JVM into a native instruction.
// bits[word] &= Long.rotateLeft(0xfffffffe,bit);
}
/**
* clears a bit.
* The index should be less than the OpenBitSet size.
*/
public void clear(long index) {
int wordNum = (int)(index >> 6); // div 64
int bit = (int)index & 0x3f; // mod 64
long bitmask = 1L << bit;
bits[wordNum / PAGE_SIZE][wordNum % PAGE_SIZE] &= ~bitmask;
}
/**
* Clears a range of bits. Clearing past the end does not change the size of the set.
*
* @param startIndex lower index
* @param endIndex one-past the last bit to clear
*/
public void clear(int startIndex, int endIndex) {
if (endIndex <= startIndex) return;
int startWord = (startIndex>>6);
if (startWord >= wlen) return;
// since endIndex is one past the end, this is index of the last
// word to be changed.
int endWord = ((endIndex-1)>>6);
long startmask = -1L << startIndex;
long endmask = -1L >>> -endIndex; // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
// invert masks since we are clearing
startmask = ~startmask;
endmask = ~endmask;
if (startWord == endWord) {
bits[startWord / PAGE_SIZE][startWord % PAGE_SIZE] &= (startmask | endmask);
return;
}
bits[startWord / PAGE_SIZE][startWord % PAGE_SIZE] &= startmask;
int middle = Math.min(wlen, endWord);
if (startWord / PAGE_SIZE == middle / PAGE_SIZE)
{
Arrays.fill(bits[startWord/PAGE_SIZE], (startWord+1) % PAGE_SIZE, middle % PAGE_SIZE, 0L);
} else
{
while (++startWord>6);
if (startWord >= wlen) return;
// since endIndex is one past the end, this is index of the last
// word to be changed.
int endWord = (int)((endIndex-1)>>6);
long startmask = -1L << startIndex;
long endmask = -1L >>> -endIndex; // 64-(endIndex&0x3f) is the same as -endIndex due to wrap
// invert masks since we are clearing
startmask = ~startmask;
endmask = ~endmask;
if (startWord == endWord) {
bits[startWord / PAGE_SIZE][startWord % PAGE_SIZE] &= (startmask | endmask);
return;
}
bits[startWord / PAGE_SIZE][startWord % PAGE_SIZE] &= startmask;
int middle = Math.min(wlen, endWord);
if (startWord / PAGE_SIZE == middle / PAGE_SIZE)
{
Arrays.fill(bits[startWord/PAGE_SIZE], (startWord+1) % PAGE_SIZE, middle % PAGE_SIZE, 0L);
} else
{
while (++startWord0;)
bitCount+=BitUtil.pop_array(bits[i],0,wlen);
return bitCount;
}
/** this = this AND other */
public void intersect(OpenBitSet other) {
int newLen= Math.min(this.wlen,other.wlen);
long[][] thisArr = this.bits;
long[][] otherArr = other.bits;
int thisPageSize = PAGE_SIZE;
int otherPageSize = OpenBitSet.PAGE_SIZE;
// testing against zero can be more efficient
int pos=newLen;
while(--pos>=0) {
thisArr[pos / thisPageSize][ pos % thisPageSize] &= otherArr[pos / otherPageSize][pos % otherPageSize];
}
if (this.wlen > newLen) {
// fill zeros from the new shorter length to the old length
for (pos=wlen;pos-->newLen;)
thisArr[pos / thisPageSize][ pos % thisPageSize] =0;
}
this.wlen = newLen;
}
// some BitSet compatability methods
//** see {@link intersect} */
public void and(OpenBitSet other) {
intersect(other);
}
/** Lowers numWords, the number of words in use,
* by checking for trailing zero words.
*/
public void trimTrailingZeros() {
int idx = wlen-1;
while (idx>=0 && bits[idx / PAGE_SIZE][idx % PAGE_SIZE]==0) idx--;
wlen = idx+1;
}
/** returns the number of 64 bit words it would take to hold numBits */
public static long bits2words(long numBits) {
return (((numBits-1)>>>6)+1);
}
/** returns true if both sets have the same bits set */
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof OpenBitSet)) return false;
OpenBitSet a;
OpenBitSet b = (OpenBitSet)o;
// make a the larger set.
if (b.wlen > this.wlen) {
a = b; b=this;
} else {
a=this;
}
int aPageSize = OpenBitSet.PAGE_SIZE;
int bPageSize = OpenBitSet.PAGE_SIZE;
// check for any set bits out of the range of b
for (int i=a.wlen-1; i>=b.wlen; i--) {
if (a.bits[i/aPageSize][i % aPageSize]!=0) return false;
}
for (int i=b.wlen-1; i>=0; i--) {
if (a.bits[i/aPageSize][i % aPageSize] != b.bits[i/bPageSize][i % bPageSize]) return false;
}
return true;
}
@Override
public int hashCode() {
// Start with a zero hash and use a mix that results in zero if the input is zero.
// This effectively truncates trailing zeros without an explicit check.
long h = 0;
for (int i = wlen; --i>=0;) {
h ^= bits[i / PAGE_SIZE][i % PAGE_SIZE];
h = (h << 1) | (h >>> 63); // rotate left
}
// fold leftmost bits into right and add a constant to prevent
// empty sets from returning 0, which is too common.
return (int)((h>>32) ^ h) + 0x98761234;
}
public void close() {
// noop, let GC do the cleanup.
}
public void serialize(DataOutput out) throws IOException {
int bitLength = getNumWords();
int pageSize = getPageSize();
int pageCount = getPageCount();
out.writeInt(bitLength);
for (int p = 0; p < pageCount; p++) {
long[] bits = getPage(p);
for (int i = 0; i < pageSize && bitLength-- > 0; i++) {
out.writeLong(bits[i]);
}
}
}
public long serializedSize() {
int bitLength = getNumWords();
int pageSize = getPageSize();
int pageCount = getPageCount();
long size = TypeSizes.sizeof(bitLength); // length
for (int p = 0; p < pageCount; p++) {
long[] bits = getPage(p);
for (int i = 0; i < pageSize && bitLength-- > 0; i++)
size += TypeSizes.sizeof(bits[i]); // bucket
}
return size;
}
public void clear() {
clear(0, capacity());
}
public static OpenBitSet deserialize(DataInput in) throws IOException {
long bitLength = in.readInt();
OpenBitSet bs = new OpenBitSet(bitLength << 6);
int pageSize = bs.getPageSize();
int pageCount = bs.getPageCount();
for (int p = 0; p < pageCount; p++) {
long[] bits = bs.getPage(p);
for (int i = 0; i < pageSize && bitLength-- > 0; i++)
bits[i] = in.readLong();
}
return bs;
}
}
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