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Generation.java
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Generation.java
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/*
* Copyright (c) 2002-2016 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.index.gbptree;
/**
* Logic for composing and decomposing stable/unstable generation number (unsigned int) to/from a single {@code long}.
*
* <pre>
* long: [S,S,S,S,U,U,U,U]
* msb <-------> lsb
* </pre>
*/
class Generation
{
private static final long UNSTABLE_GENERATION_MASK = 0xFFFFFFFFL;
private static final int STABLE_GENERATION_SHIFT = Integer.SIZE;
/**
* Takes one stable and one unstable generation (both unsigned ints) and crams them into one {@code long}.
*
* @param stableGeneration stable generation.
* @param unstableGeneration unstable generation.
* @return the two generation numbers as one {@code long}.
*/
public static long generation( long stableGeneration, long unstableGeneration )
{
GenSafePointer.assertGenerationOnWrite( stableGeneration );
GenSafePointer.assertGenerationOnWrite( unstableGeneration );
return (stableGeneration << STABLE_GENERATION_SHIFT) | unstableGeneration;
}
/**
* Extracts and returns unstable generation from generation {@code long}.
*
* @param generation generation variable containing both stable and unstable generations.
* @return unstable generation from generation.
*/
public static long unstableGeneration( long generation )
{
return generation & UNSTABLE_GENERATION_MASK;
}
/**
* Extracts and returns stable generation from generation {@code long}.
*
* @param generation generation variable containing both stable and unstable generations.
* @return stable generation from generation.
*/
public static long stableGeneration( long generation )
{
return generation >>> STABLE_GENERATION_SHIFT;
}
}