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/*
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* Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package sun.misc;
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import java.util.Random;
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/**
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* Hashing utilities.
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*
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* Little endian implementations of Murmur3 hashing.
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*/
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public class Hashing {
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/**
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* Static utility methods only.
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*/
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private Hashing() {
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throw new Error("No instances");
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}
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public static int murmur3_32(byte[] data) {
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return murmur3_32(0, data, 0, data.length);
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}
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public static int murmur3_32(int seed, byte[] data) {
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return murmur3_32(seed, data, 0, data.length);
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}
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@SuppressWarnings("fallthrough")
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public static int murmur3_32(int seed, byte[] data, int offset, int len) {
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int h1 = seed;
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int count = len;
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// body
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while (count >= 4) {
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int k1 = (data[offset] & 0x0FF)
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| (data[offset + 1] & 0x0FF) << 8
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| (data[offset + 2] & 0x0FF) << 16
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| data[offset + 3] << 24;
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count -= 4;
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offset += 4;
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k1 *= 0xcc9e2d51;
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k1 = Integer.rotateLeft(k1, 15);
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k1 *= 0x1b873593;
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h1 ^= k1;
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h1 = Integer.rotateLeft(h1, 13);
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h1 = h1 * 5 + 0xe6546b64;
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}
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// tail
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if (count > 0) {
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int k1 = 0;
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switch (count) {
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case 3:
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k1 ^= (data[offset + 2] & 0xff) << 16;
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// fall through
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case 2:
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k1 ^= (data[offset + 1] & 0xff) << 8;
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// fall through
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case 1:
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k1 ^= (data[offset] & 0xff);
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// fall through
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default:
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k1 *= 0xcc9e2d51;
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k1 = Integer.rotateLeft(k1, 15);
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k1 *= 0x1b873593;
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h1 ^= k1;
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}
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}
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// finalization
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h1 ^= len;
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// finalization mix force all bits of a hash block to avalanche
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h1 ^= h1 >>> 16;
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h1 *= 0x85ebca6b;
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h1 ^= h1 >>> 13;
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h1 *= 0xc2b2ae35;
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h1 ^= h1 >>> 16;
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return h1;
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}
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public static int murmur3_32(char[] data) {
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return murmur3_32(0, data, 0, data.length);
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}
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public static int murmur3_32(int seed, char[] data) {
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return murmur3_32(seed, data, 0, data.length);
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}
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public static int murmur3_32(int seed, char[] data, int offset, int len) {
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int h1 = seed;
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int off = offset;
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int count = len;
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// body
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while (count >= 2) {
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int k1 = (data[off++] & 0xFFFF) | (data[off++] << 16);
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count -= 2;
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k1 *= 0xcc9e2d51;
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k1 = Integer.rotateLeft(k1, 15);
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k1 *= 0x1b873593;
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h1 ^= k1;
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h1 = Integer.rotateLeft(h1, 13);
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h1 = h1 * 5 + 0xe6546b64;
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}
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// tail
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if (count > 0) {
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int k1 = data[off];
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k1 *= 0xcc9e2d51;
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k1 = Integer.rotateLeft(k1, 15);
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k1 *= 0x1b873593;
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h1 ^= k1;
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}
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// finalization
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h1 ^= len * (Character.SIZE / Byte.SIZE);
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// finalization mix force all bits of a hash block to avalanche
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h1 ^= h1 >>> 16;
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h1 *= 0x85ebca6b;
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h1 ^= h1 >>> 13;
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h1 *= 0xc2b2ae35;
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h1 ^= h1 >>> 16;
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return h1;
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}
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public static int murmur3_32(int[] data) {
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return murmur3_32(0, data, 0, data.length);
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}
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public static int murmur3_32(int seed, int[] data) {
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return murmur3_32(seed, data, 0, data.length);
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}
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public static int murmur3_32(int seed, int[] data, int offset, int len) {
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int h1 = seed;
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int off = offset;
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int end = offset + len;
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// body
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while (off < end) {
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int k1 = data[off++];
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k1 *= 0xcc9e2d51;
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k1 = Integer.rotateLeft(k1, 15);
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k1 *= 0x1b873593;
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h1 ^= k1;
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h1 = Integer.rotateLeft(h1, 13);
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h1 = h1 * 5 + 0xe6546b64;
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}
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// tail (always empty, as body is always 32-bit chunks)
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// finalization
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h1 ^= len * (Integer.SIZE / Byte.SIZE);
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// finalization mix force all bits of a hash block to avalanche
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h1 ^= h1 >>> 16;
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h1 *= 0x85ebca6b;
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h1 ^= h1 >>> 13;
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h1 *= 0xc2b2ae35;
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h1 ^= h1 >>> 16;
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return h1;
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}
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/**
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* Holds references to things that can't be initialized until after VM
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* is fully booted.
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*/
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private static class Holder {
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/**
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* Used for generating per-instance hash seeds.
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*
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* We try to improve upon the default seeding.
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*/
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static final Random SEED_MAKER = new Random(
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Double.doubleToRawLongBits(Math.random())
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^ System.identityHashCode(Hashing.class)
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^ System.currentTimeMillis()
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^ System.nanoTime()
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^ Runtime.getRuntime().freeMemory());
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}
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public static int randomHashSeed(Object instance) {
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int seed;
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if (sun.misc.VM.isBooted()) {
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seed = Holder.SEED_MAKER.nextInt();
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} else {
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// lower quality "random" seed value--still better than zero and not
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// not practically reversible.
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int hashing_seed[] = {
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System.identityHashCode(Hashing.class),
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System.identityHashCode(instance),
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System.identityHashCode(Thread.currentThread()),
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(int) Thread.currentThread().getId(),
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(int) (System.currentTimeMillis() >>> 2), // resolution is poor
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(int) (System.nanoTime() >>> 5), // resolution is poor
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(int) (Runtime.getRuntime().freeMemory() >>> 4) // alloc min
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};
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seed = murmur3_32(hashing_seed);
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}
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// force to non-zero.
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return (0 != seed) ? seed : 1;
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}
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}
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