127 lines
4.7 KiB
Java
127 lines
4.7 KiB
Java
// ============================================================================
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// Copyright 2006-2012 Daniel W. Dyer
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// ============================================================================
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package net.citizensnpcs.util;
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import java.util.Random;
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import java.util.concurrent.locks.ReentrantLock;
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/**
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* <p>
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* Very fast pseudo random number generator. See
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* <a href= "http://school.anhb.uwa.edu.au/personalpages/kwessen/shared/Marsaglia03.html" >this page</a> for a
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* description. This RNG has a period of about 2^160, which is not as long as the MersenneTwisterRNG but it is faster.
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* </p>
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*
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* <p>
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* <em>NOTE: Because instances of this class require 160-bit seeds, it is not possible to seed this RNG using the
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* {@link #setSeed(long)} method inherited from {@link Random}. Calls to this method will have no effect. Instead the
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* seed must be set by a constructor.</em>
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* </p>
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*
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* @author Daniel Dyer
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* @since 1.2
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*/
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public class XORShiftRNG extends Random {
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// Lock to prevent concurrent modification of the RNG's internal state.
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private final ReentrantLock lock = new ReentrantLock();
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private final byte[] seed;
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// Previously used an array for state but using separate fields proved to be
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// faster.
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private int state1;
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private int state2;
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private int state3;
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private int state4;
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private int state5;
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/**
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* Creates an RNG and seeds it with the specified seed data.
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*
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*/
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public XORShiftRNG() {
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this.seed = new byte[SEED_SIZE_BYTES];
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SEED_GENERATOR.nextBytes(seed);
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int[] state = convertBytesToInts(seed);
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this.state1 = state[0];
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this.state2 = state[1];
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this.state3 = state[2];
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this.state4 = state[3];
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this.state5 = state[4];
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}
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public byte[] getSeed() {
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return seed.clone();
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}
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@Override
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protected int next(int bits) {
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try {
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lock.lock();
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int t = state1 ^ state1 >> 7;
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state1 = state2;
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state2 = state3;
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state3 = state4;
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state4 = state5;
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state5 = state5 ^ state5 << 6 ^ t ^ t << 13;
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int value = (state2 + state2 + 1) * state5;
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return value >>> 32 - bits;
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} finally {
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lock.unlock();
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}
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}
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/**
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* Take four bytes from the specified position in the specified block and convert them into a 32-bit int, using the
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* big-endian convention.
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*
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* @param bytes
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* The data to read from.
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* @param offset
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* The position to start reading the 4-byte int from.
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* @return The 32-bit integer represented by the four bytes.
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*/
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public static int convertBytesToInt(byte[] bytes, int offset) {
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return BITWISE_BYTE_TO_INT & bytes[offset + 3] | (BITWISE_BYTE_TO_INT & bytes[offset + 2]) << 8
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| (BITWISE_BYTE_TO_INT & bytes[offset + 1]) << 16 | (BITWISE_BYTE_TO_INT & bytes[offset]) << 24;
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}
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/**
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* Convert an array of bytes into an array of ints. 4 bytes from the input data map to a single int in the output
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* data.
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*
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* @param bytes
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* The data to read from.
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* @return An array of 32-bit integers constructed from the data.
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* @since 1.1
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*/
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public static int[] convertBytesToInts(byte[] bytes) {
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if (bytes.length % 4 != 0)
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throw new IllegalArgumentException("Number of input bytes must be a multiple of 4.");
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int[] ints = new int[bytes.length / 4];
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for (int i = 0; i < ints.length; i++) {
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ints[i] = convertBytesToInt(bytes, i * 4);
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}
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return ints;
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}
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// Mask for casting a byte to an int, bit-by-bit (with
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// bitwise AND) with no special consideration for the sign bit.
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private static final int BITWISE_BYTE_TO_INT = 0x000000FF;
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private static Random SEED_GENERATOR = new Random();
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private static final int SEED_SIZE_BYTES = 20; // Needs 5 32-bit integers.
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private static final long serialVersionUID = -1843001897066722618L;
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} |