smile.hash.MurmurHash2 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 smile.hash;
import java.nio.ByteBuffer;
/**
* MurmurHash is a very fast, non-cryptographic hash suitable for general hash-based
* lookup. The name comes from two basic operations, multiply (MU) and rotate (R),
* used in its inner loop. See http://murmurhash.googlepages.com/ for more details.
*
* The older MurmurHash2 yields a 32-bit or 64-bit value.
*
* This class is adapted from Apache Cassandra.
*
* @see MurmurHash3
*
* @author Haifeng Li
*/
public class MurmurHash2 {
/** 32-bit MurmurHash. */
public static int hash32(ByteBuffer data, int offset, int length, int seed) {
int m = 0x5bd1e995;
int r = 24;
int h = seed ^ length;
int len_4 = length >> 2;
for (int i = 0; i < len_4; i++) {
int i_4 = i << 2;
int k = data.get(offset + i_4 + 3);
k = k << 8;
k = k | (data.get(offset + i_4 + 2) & 0xff);
k = k << 8;
k = k | (data.get(offset + i_4 + 1) & 0xff);
k = k << 8;
k = k | (data.get(offset + 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) {
if (left >= 3) {
h ^= (int) data.get(offset + length - 3) << 16;
}
if (left >= 2) {
h ^= (int) data.get(offset + length - 2) << 8;
}
if (left >= 1) {
h ^= (int) data.get(offset + length - 1);
}
h *= m;
}
h ^= h >>> 13;
h *= m;
h ^= h >>> 15;
return h;
}
/** 64-bit MurmurHash. */
public static long hash64(ByteBuffer key, int offset, int length, long seed) {
long m64 = 0xc6a4a7935bd1e995L;
int r64 = 47;
long h64 = (seed & 0xffffffffL) ^ (m64 * length);
int lenLongs = length >> 3;
for (int i = 0; i < lenLongs; ++i) {
int i_8 = i << 3;
long k64 = ((long) key.get(offset + i_8 + 0) & 0xff)
+ (((long) key.get(offset + i_8 + 1) & 0xff) << 8)
+ (((long) key.get(offset + i_8 + 2) & 0xff) << 16)
+ (((long) key.get(offset + i_8 + 3) & 0xff) << 24)
+ (((long) key.get(offset + i_8 + 4) & 0xff) << 32)
+ (((long) key.get(offset + i_8 + 5) & 0xff) << 40)
+ (((long) key.get(offset + i_8 + 6) & 0xff) << 48)
+ (((long) key.get(offset + i_8 + 7) & 0xff) << 56);
k64 *= m64;
k64 ^= k64 >>> r64;
k64 *= m64;
h64 ^= k64;
h64 *= m64;
}
int rem = length & 0x7;
switch (rem) {
case 0:
break;
case 7:
h64 ^= (long) key.get(offset + length - rem + 6) << 48;
case 6:
h64 ^= (long) key.get(offset + length - rem + 5) << 40;
case 5:
h64 ^= (long) key.get(offset + length - rem + 4) << 32;
case 4:
h64 ^= (long) key.get(offset + length - rem + 3) << 24;
case 3:
h64 ^= (long) key.get(offset + length - rem + 2) << 16;
case 2:
h64 ^= (long) key.get(offset + length - rem + 1) << 8;
case 1:
h64 ^= (long) key.get(offset + length - rem);
h64 *= m64;
}
h64 ^= h64 >>> r64;
h64 *= m64;
h64 ^= h64 >>> r64;
return h64;
}
}