org.h2.util.HashBase Maven / Gradle / Ivy
/*
* Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.util;
/**
* The base for other hash classes.
*/
public abstract class HashBase {
/**
* The maximum load, in percent.
* declared as long so we do long arithmetic so we don't overflow.
*/
private static final long MAX_LOAD = 90;
/**
* The bit mask to get the index from the hash code.
*/
protected int mask;
/**
* The number of slots in the table.
*/
protected int len;
/**
* The number of occupied slots, excluding the zero key (if any).
*/
protected int size;
/**
* The number of deleted slots.
*/
protected int deletedCount;
/**
* The level. The number of slots is 2 ^ level.
*/
protected int level;
/**
* Whether the zero key is used.
*/
protected boolean zeroKey;
private int maxSize, minSize, maxDeleted;
public HashBase() {
reset(2);
}
/**
* Increase the size of the underlying table and re-distribute the elements.
*
* @param newLevel the new level
*/
protected abstract void rehash(int newLevel);
/**
* Get the size of the map.
*
* @return the size
*/
public int size() {
return size + (zeroKey ? 1 : 0);
}
/**
* Check the size before adding an entry. This method resizes the map if
* required.
*/
void checkSizePut() {
if (deletedCount > size) {
rehash(level);
}
if (size + deletedCount >= maxSize) {
rehash(level + 1);
}
}
/**
* Check the size before removing an entry. This method resizes the map if
* required.
*/
protected void checkSizeRemove() {
if (size < minSize && level > 0) {
rehash(level - 1);
} else if (deletedCount > maxDeleted) {
rehash(level);
}
}
/**
* Clear the map and reset the level to the specified value.
*
* @param newLevel the new level
*/
protected void reset(int newLevel) {
// can't exceed 30 or we will generate a negative value
// for the "len" field
if (newLevel > 30) {
throw new IllegalStateException("exceeded max size of hash table");
}
size = 0;
level = newLevel;
len = 2 << level;
mask = len - 1;
minSize = (int) ((1 << level) * MAX_LOAD / 100);
maxSize = (int) (len * MAX_LOAD / 100);
deletedCount = 0;
maxDeleted = 20 + len / 2;
}
/**
* Calculate the index for this hash code.
*
* @param hash the hash code
* @return the index
*/
protected int getIndex(int hash) {
return hash & mask;
}
}