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org.apache.solr.util.hll.BitUtil Maven / Gradle / Ivy
/*
* 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.solr.util.hll;
/**
* A collection of bit utilities.
*/
class BitUtil {
/**
* The set of least-significant bits for a given byte. -1
* is used if no bits are set (so as to not be confused with "index of zero"
* meaning that the least significant bit is the 0th (1st) bit).
*
* @see #leastSignificantBit(long)
*/
private static final int[] LEAST_SIGNIFICANT_BIT = {
-1, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};
/**
* Computes the least-significant bit of the specified long
* that is set to 1. Zero-indexed.
*
* @param value the long whose least-significant bit is desired.
* @return the least-significant bit of the specified long.
* -1 is returned if there are no bits set.
*/
// REF: http://stackoverflow.com/questions/757059/position-of-least-significant-bit-that-is-set
// REF: http://www-graphics.stanford.edu/~seander/bithacks.html
public static int leastSignificantBit(final long value) {
if(value == 0L) return -1/*by contract*/;
if((value & 0xFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 0) & 0xFF)] + 0;
if((value & 0xFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 8) & 0xFF)] + 8;
if((value & 0xFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 16) & 0xFF)] + 16;
if((value & 0xFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 24) & 0xFF)] + 24;
if((value & 0xFFFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 32) & 0xFF)] + 32;
if((value & 0xFFFFFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 40) & 0xFF)] + 40;
if((value & 0xFFFFFFFFFFFFFFL) != 0) return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 48) & 0xFF)] + 48;
return LEAST_SIGNIFICANT_BIT[(int)( (value >>> 56) & 0xFFL)] + 56;
}
}
