org.apache.hive.common.util.HashCodeUtil Maven / Gradle / Ivy
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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.hive.common.util;
/*
* Common hash code routines.
*/
public class HashCodeUtil {
public static int calculateIntHashCode(int key) {
key = ~key + (key << 15); // key = (key << 15) - key - 1;
key = key ^ (key >>> 12);
key = key + (key << 2);
key = key ^ (key >>> 4);
key = key * 2057; // key = (key + (key << 3)) + (key << 11);
key = key ^ (key >>> 16);
return key;
}
public static int calculateLongHashCode(long key) {
// Mixing down into the lower bits - this produces a worse hashcode in purely
// numeric terms, but leaving entropy in the higher bits is not useful for a
// 2^n bucketing scheme. See JSR166 ConcurrentHashMap r1.89 (released under Public Domain)
// Note: ConcurrentHashMap has since reverted this to retain entropy bits higher
// up, to support the 2-level hashing for segment which operates at a higher bitmask
key ^= (key >>> 7) ^ (key >>> 4);
key ^= (key >>> 20) ^ (key >>> 12);
return (int) key;
}
public static void calculateLongArrayHashCodes(long[] longs, int[] hashCodes, final int count) {
for (int v = 0; v < count; v++) {
hashCodes[v] = (int) calculateLongHashCode(longs[v]);
}
}
public static int calculateBytesHashCode(byte[] keyBytes, int keyStart, int keyLength) {
return murmurHash(keyBytes, keyStart, keyLength);
}
public static void calculateBytesArrayHashCodes(byte[][] bytesArrays,
int[] starts, int[] lengths, int[] valueSelected, int[] hashCodes, final int count) {
for (int i = 0; i < count; i++) {
int batchIndex = valueSelected[i];
hashCodes[i] = murmurHash(bytesArrays[batchIndex], starts[batchIndex],
lengths[batchIndex]);
}
}
// Lifted from org.apache.hadoop.util.hash.MurmurHash... but supports offset.
// Must produce the same result as MurmurHash.hash with seed = 0.
public static int murmurHash(byte[] data, int offset, int length) {
int m = 0x5bd1e995;
int r = 24;
int h = length;
int len_4 = length >> 2;
for (int i = 0; i < len_4; i++) {
int i_4 = offset + (i << 2);
int k = data[i_4 + 3];
k = k << 8;
k = k | (data[i_4 + 2] & 0xff);
k = k << 8;
k = k | (data[i_4 + 1] & 0xff);
k = k << 8;
k = k | (data[i_4 + 0] & 0xff);
k *= m;
k ^= k >>> r;
k *= m;
h *= m;
h ^= k;
}
// avoid calculating modulo
int len_m = len_4 << 2;
int left = length - len_m;
if (left != 0) {
length += offset;
if (left >= 3) {
h ^= (int) data[length - 3] << 16;
}
if (left >= 2) {
h ^= (int) data[length - 2] << 8;
}
if (left >= 1) {
h ^= (int) data[length - 1];
}
h *= m;
}
h ^= h >>> 13;
h *= m;
h ^= h >>> 15;
return h;
}
}