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/*
* 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.spark.unsafe.bitset;
import org.apache.spark.unsafe.Platform;
/**
* Methods for working with fixed-size uncompressed bitsets.
*
* We assume that the bitset data is word-aligned (that is, a multiple of 8 bytes in length).
*
* Each bit occupies exactly one bit of storage.
*/
public final class BitSetMethods {
private static final long WORD_SIZE = 8;
private BitSetMethods() {
// Make the default constructor private, since this only holds static methods.
}
/**
* Sets the bit at the specified index to {@code true}.
*/
public static void set(Object baseObject, long baseOffset, int index) {
assert index >= 0 : "index (" + index + ") should >= 0";
final long mask = 1L << (index & 0x3f); // mod 64 and shift
final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
final long word = Platform.getLong(baseObject, wordOffset);
Platform.putLong(baseObject, wordOffset, word | mask);
}
/**
* Sets the bit at the specified index to {@code false}.
*/
public static void unset(Object baseObject, long baseOffset, int index) {
assert index >= 0 : "index (" + index + ") should >= 0";
final long mask = 1L << (index & 0x3f); // mod 64 and shift
final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
final long word = Platform.getLong(baseObject, wordOffset);
Platform.putLong(baseObject, wordOffset, word & ~mask);
}
/**
* Returns {@code true} if the bit is set at the specified index.
*/
public static boolean isSet(Object baseObject, long baseOffset, int index) {
assert index >= 0 : "index (" + index + ") should >= 0";
final long mask = 1L << (index & 0x3f); // mod 64 and shift
final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
final long word = Platform.getLong(baseObject, wordOffset);
return (word & mask) != 0;
}
/**
* Returns {@code true} if any bit is set.
*/
public static boolean anySet(Object baseObject, long baseOffset, long bitSetWidthInWords) {
long addr = baseOffset;
for (int i = 0; i < bitSetWidthInWords; i++, addr += WORD_SIZE) {
if (Platform.getLong(baseObject, addr) != 0) {
return true;
}
}
return false;
}
/**
* Returns the index of the first bit that is set to true that occurs on or after the
* specified starting index. If no such bit exists then {@code -1} is returned.
* <p>
* To iterate over the true bits in a BitSet, use the following loop:
* <pre>
* <code>
* for (long i = bs.nextSetBit(0, sizeInWords); i >= 0; i = bs.nextSetBit(i + 1, sizeInWords)) {
* // operate on index i here
* }
* </code>
* </pre>
*
* @param fromIndex the index to start checking from (inclusive)
* @param bitsetSizeInWords the size of the bitset, measured in 8-byte words
* @return the index of the next set bit, or -1 if there is no such bit
*/
public static int nextSetBit(
Object baseObject,
long baseOffset,
int fromIndex,
int bitsetSizeInWords) {
int wi = fromIndex >> 6;
if (wi >= bitsetSizeInWords) {
return -1;
}
// Try to find the next set bit in the current word
final int subIndex = fromIndex & 0x3f;
long word = Platform.getLong(baseObject, baseOffset + wi * WORD_SIZE) >> subIndex;
if (word != 0) {
return (wi << 6) + subIndex + java.lang.Long.numberOfTrailingZeros(word);
}
// Find the next set bit in the rest of the words
wi += 1;
while (wi < bitsetSizeInWords) {
word = Platform.getLong(baseObject, baseOffset + wi * WORD_SIZE);
if (word != 0) {
return (wi << 6) + java.lang.Long.numberOfTrailingZeros(word);
}
wi += 1;
}
return -1;
}
}
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